tag:theconversation.com,2011:/global/topics/calendars-25237/articlesCalendars – The Conversation2024-02-28T01:00:24Ztag:theconversation.com,2011:article/2245032024-02-28T01:00:24Z2024-02-28T01:00:24ZLeap of imagination: how February 29 reminds us of our mysterious relationship with time and space<p>If you find it intriguing that February 28 will be followed this week by February 29, rather than March 1 as it usually is, spare a thought for those alive in 1582. Back then, Thursday October 4 was followed by Friday October 15.</p>
<p>Ten whole days were snatched from the present when Pope Gregory XIII issued a papal bull to “restore” the calendar from discrepancies that had crept into the Julian calendar, introduced by Julius Caesar in 45 BCE.</p>
<p>The new Gregorian calendar returned the northern hemisphere’s vernal equinox to its “proper” place, around March 21. (The equinox is when the Earth’s axis is tilted neither toward nor away from the sun, and is used to determine the date of Easter.) </p>
<p>The Julian calendar had observed a leap year every four years, but this meant time had drifted out of alignment with the dates of celestial events and astronomical seasons. </p>
<p>In the Gregorian calendar, leap days were added only to years that were a multiple of four – like 2024 – with an exception for years that were evenly divisible by 100, but not 400 – like 1700.</p>
<p>Simply put, leap days exist because it doesn’t take a neat 365 days for Earth to orbit the Sun. It takes 365.2422 days. Tracking the movement of celestial objects through space in an orderly pattern doesn’t quite work, which is why we have February – time’s great mop.</p>
<h2>Time and space</h2>
<p>This is just part of the history of how February – the shortest month, and originally the last month in the Roman calendar – came to have the job of absorbing those inconsistencies in the temporal calculations of the world’s most commonly used calendar.</p>
<p>There is plenty of <a href="https://theconversation.com/leap-day-fixing-the-faults-in-our-stars-54032">science</a>, <a href="https://theconversation.com/explainer-the-science-behind-leap-years-and-how-they-work-54788">maths</a> and <a href="https://theconversation.com/how-a-seasonal-snarl-up-in-the-mid-1500s-gave-us-our-strange-rules-for-leap-years-132659">astrophysics</a> explaining the relationship between time and the planet we live on. But I like to think leap years and days offer something even more interesting to consider: why do we have calendars anyway?</p>
<p>And what have they got to do with how we understand the wonder and strangeness of our existence in the universe? Because calendars tell a story, not just about time, but also about space.</p>
<p>Our reckoning of time on Earth is through our spatial relationship to the Sun, Moon and stars. Time, and its place in our lives, sits somewhere between the scientific, the celestial and the spiritual. </p>
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Read more:
<a href="https://theconversation.com/why-does-a-leap-year-have-366-days-218330">Why does a leap year have 366 days?</a>
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<p>It is <a href="https://shop.whitechapelgallery.org/products/time">notoriously slippery, subjective and experiential</a>. It is also marked, tracked and determined in myriad ways across different cultures, from tropical to solar to <a href="https://www.stuff.co.nz/pou-tiaki/300062097/matariki-and-the-maramataka-the-mori-lunar-calendar">lunar</a> calendars.</p>
<p>It is the Sun that measures a day and gives us our first reference point for understanding time. But it is the <a href="https://librarysearch.aut.ac.nz/vufind/Record/1145999?sid=25214690">Moon</a>, as a major celestial body, that extends our perception of time. By stretching a span of one day into something longer, it offers us a chance for philosophical reflection.</p>
<p>The Sun (or its effect at least) is either present or not present. The Moon, however, goes through phases of transformation. It appears and disappears, changing shape and hinting that one night is not exactly like the one before or after.</p>
<p>The Moon also has a distinct rhythm that can be tracked and understood as a pattern, giving us another sense of duration. Time is just that – overlapping durations: instants, seconds, minutes, hours, days, weeks, months, years, decades, lifetimes, centuries, ages.</p>
<h2>The elusive Moon</h2>
<p>It is almost impossible to imagine how time might feel in the absence of all the tools and gadgets we use to track, control and corral it. But it’s also hard to know what we might do in the absence of time as a unit of productivity – a measurable, dispensable resource.</p>
<p>The closest we might come is simply to imagine what life might feel like in the absence of the Moon. Each day would rise and fall, in a rhythm of its own, but without visible reference to anything else. Just endless shifts from light to dark.</p>
<p>Nights would be almost completely dark without the light of the Moon. Only stars at a much further distance would puncture the inky sky. The world around us would change – trees would grow, mammals would age and die, land masses would shift and change – but all would happen in an endless cycle of sunrise to sunset.</p>
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Read more:
<a href="https://theconversation.com/scientists-are-hoping-to-redefine-the-second-heres-why-157645">Scientists are hoping to redefine the second – here's why</a>
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<p>The light from the Sun takes <a href="https://www.skyatnightmagazine.com/space-science/how-take-light-from-sun-reach-earth">eight minutes</a> to reach Earth, so the sunlight we see is always eight minutes in the past. </p>
<p>I remember sitting outside when I first learned this, and wondering what the temporal delay might be between me and other objects: a plum tree, trees at the end of the street, hills in the distance, light on the horizon when looking out over the ocean, stars in the night sky.</p>
<p>Moonlight, for reference, takes about <a href="https://www.pbs.org/seeinginthedark/astronomy-topics/light-as-a-cosmic-time-machine.html">1.3 seconds</a> to get to Earth. Light always travels at the same speed, it is entirely constant. The differing duration between how long it takes for sunlight or moonlight to reach the Earth is determined by the space in between. </p>
<p>Time on the other hand, is anything but constant. There are countless ways we characterise it. The mere fact we have so many calendars and ways of describing perceptual time hints at our inability to pin it down. </p>
<p>Calendars give us the impression we can, and have, made time predictable and understandable. Leap years, days and seconds serve as a periodic reminder that we haven’t.</p><img src="https://counter.theconversation.com/content/224503/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emily O'Hara does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>2024 is a leap year, when the shortest month mops up a bit of leftover time. But the extra day also tells us about space – and our place in it.Emily O'Hara, Senior Lecturer, Spatial Design + Temporary Practices, Auckland University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2183302024-02-19T13:36:56Z2024-02-19T13:36:56ZWhy does a leap year have 366 days?<figure><img src="https://images.theconversation.com/files/575717/original/file-20240214-24-h6q6if.jpg?ixlib=rb-1.1.0&rect=38%2C23%2C5137%2C3422&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Leap Day is coming.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/calendar-on-february-29-on-a-leap-year-leap-day-royalty-free-image/1196849410">Marvin Samuel Tolentino Pineda/iStock, via Getty images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<blockquote>
<p>Why does a leap year have 366 days? Does the Earth move slower every four years? – Aarush, age 8, Milpitas, California</p>
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<p>You may be used to hearing that it takes the Earth 365 days to make a full lap, but that journey actually lasts about 365 and a quarter days. Leap years help to keep the 12-month calendar matched up with Earth’s movement around the Sun. </p>
<p>After four years, those leftover hours add up to a whole day. In a leap year, we add this extra day to the month of February, making it 29 days long instead of the usual 28.</p>
<p>The idea of an annual catch-up dates back to ancient Rome, where people had a calendar with 355 days instead of 365 because it was based on cycles and phases of the Moon. They noticed that their calendar was getting out of sync with the seasons, so they began adding an extra month, <a href="https://www.britannica.com/science/Roman-republican-calendar">which they called Mercedonius</a>, every two years to catch up with the missing days.</p>
<p>In the year 45 B.C.E., Roman emperor Julius Caesar introduced a solar calendar, based on one developed in Egypt. Every four years, February received an extra day to keep the calendar in line with the Earth’s journey around the Sun. In honor of Caesar, this system is still known as the Julian calendar.</p>
<p>But that wasn’t the last tweak. As time went on, people realized that the Earth’s journey wasn’t exactly 365.25 days – it <a href="https://airandspace.si.edu/stories/editorial/science-leap-year">actually took 365.24219 days</a>, which is about 11 minutes less. So adding a whole day every four years was actually a little more correction than was needed. </p>
<p>In 1582, Pope Gregory XIII signed an order that made a small adjustment. There would still be a leap year every four years, except in “century” years – years divisible by 100, like 1700 or 2100 – unless they were also divisible by 400. It might sound a bit like a puzzle, but this adjustment made the calendar <a href="https://airandspace.si.edu/stories/editorial/science-leap-year">even more accurate</a> – and from that point on, it was known as the Gregorian calendar.</p>
<h2>What if we didn’t have leap years?</h2>
<p>If the calendar didn’t make that small correction every four years, it would gradually fall out of alignment with the seasons. Over centuries, this could lead to the <a href="https://www.britannica.com/story/whats-the-difference-between-a-solstice-and-an-equinox">solstices and equinoxes</a> occurring at different times than expected. Winter weather might develop in what the calendar showed as summer, and farmers could become confused about when to plant their seeds.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/YTOr8_ILqGw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Without leap years, our calendar would gradually become disconnected from the seasons.</span></figcaption>
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<p>Other calendars around the world have their own ways of keeping time. The Jewish calendar, which is regulated by <a href="https://www.britannica.com/topic/Jewish-religious-year">both the Moon and the Sun</a>, is like a big puzzle with a 19-year cycle. Every now and then, it adds a leap month to make sure that special celebrations happen at just the right time. </p>
<p>The <a href="https://ing.org/resources/for-all-groups/calendar-of-important-islamic-dates/">Islamic calendar</a> is even more unusual. It follows the <a href="https://spaceplace.nasa.gov/moon-phases/en/">phases of the Moon</a> and doesn’t add extra days. Since a lunar year is only about 355 days long, key dates on the Islamic calendar move 10 to 11 days earlier each year on the solar calendar. </p>
<p>For example, Ramadan, the <a href="https://ing.org/resources/for-all-groups/calendar-of-important-islamic-dates/">Islamic month of fasting</a>, falls in the ninth month of the Islamic calendar. In 2024, it will run from March 11 to April 9; in 2025, it will occur from March 1-29; and in 2026, it will be celebrated from Feb. 18 to March 19.</p>
<h2>Learning from the planets</h2>
<p>Astronomy originated as a way to make sense of our daily lives, linking the events around us to celestial phenomena. The concept of leap years exemplifies how, from early ages, humans found order in conditions that seemed chaotic. </p>
<p>Simple, unsophisticated but effective tools, born from creative ideas of ancient astronomers and visionaries, provided the first glimpses into understanding the nature that envelops us. Some <a href="https://www.britannica.com/science/astronomy/History-of-astronomy">ancient methods</a>, such as <a href="https://sci.esa.int/web/gaia/-/53196-the-oldest-sky-maps">astrometry and lists of astronomical objects</a>, persist even today, revealing the timeless essence of our quest to understand nature. </p>
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<a href="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Photograph of an intricate schematic guide to the night sky." src="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=356&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=356&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=356&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=447&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=447&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=447&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Ancient Egyptians were dedicated astronomers. This section from the ceiling of the tomb of Senenmut, a high court official in Egypt, was drawn sometime circa 1479–1458 B.C.E. It shows constellations, protective gods and 24 segmented wheels for the hours of the day and the months of the year.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Senenmut-Grab.JPG">NebMaatRa/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>People who do research in physics and astronomy, the <a href="https://scholar.google.com/citations?user=t4L_D18AAAAJ&hl=en">field that I study</a>, are inherently curious about the workings of the universe and our origins. This work is exciting, and also extremely humbling; it constantly shows that in the grand scheme, our lives occupy a mere second in the vast expanse of space and time – even in leap years when we add that extra day.</p>
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<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/218330/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bhagya Subrayan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Humans have synced their calendars to the sun and moon for centuries, but every so often, these systems need a little correction.Bhagya Subrayan, PhD Student in Physics and Astronomy, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2119782023-12-28T09:17:12Z2023-12-28T09:17:12ZA brief history of time – as told by a watchmaker<figure><img src="https://images.theconversation.com/files/556286/original/file-20231027-27-lyxm9y.jpg?ixlib=rb-1.1.0&rect=26%2C57%2C3468%2C2038&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/antique-old-spiral-clock-abstract-fractal-765452851">Mikhail Leonov/Shutterstock</a></span></figcaption></figure><p>I once restored a 1950s timepiece for a customer who waxed lyrical about the intricacies of my work – all the while refusing to pay. They baulked when I presented them with the bill we’d previously agreed. Then they garbled on about the philosophical nature of time, still resisting payment. </p>
<p>It was during that wistful, skyward narrative that I saw the timepiece slip from their hand and hit the marble floor. The mineral glass shattered, sending the hands spiralling. Sunlight streamed in from the winter setting Sun – its sharp, angular rays reminding me of how our ancient ancestors marked the passing of time. </p>
<p>Time was important enough to our ancestors that they went to the effort of building an extraordinary prehistoric monument, Stonehenge. The first part of this <a href="https://www.cambridge.org/core/journals/antiquity/article/keeping-time-at-stonehenge/792A5E8E091C8B7CB9C26B4A35A6B399">enormous solar calendar</a> was built around 2200-2400BC.</p>
<p>But it is far from unique – primeval solar observatories are dotted around the world, including the <a href="https://whc.unesco.org/en/list/1624/">Chankillo mounds in Peru</a> (built in 200-250BC) and the Australian Aboriginal <a href="https://search.informit.org/doi/abs/10.3316/informit.488037339209650">Wurdi Youang</a> stone arrangement (age unknown). Societies around the world, thousands of miles apart, independently created sites to help mark the passing of time. </p>
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<img alt="Stonehenge during sunset" src="https://images.theconversation.com/files/556285/original/file-20231027-26-7jbdxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/556285/original/file-20231027-26-7jbdxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/556285/original/file-20231027-26-7jbdxx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/556285/original/file-20231027-26-7jbdxx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/556285/original/file-20231027-26-7jbdxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/556285/original/file-20231027-26-7jbdxx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/556285/original/file-20231027-26-7jbdxx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Stonehenge was built as a kind of solar calendar.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/stonehenge-during-sunset-winter-solstice-1601037709">Chuta Kooanantkul/Shutterstock</a></span>
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<h2>It’s in the timing</h2>
<p>As communities <a href="https://www.penguin.co.uk/books/311482/about-time-by-rooney-david/9780241370513">developed</a> into cities, empires and states, and societies became more segregated, time became more important and was divided into hours.</p>
<p><a href="https://www.worldhistory.org/Sumerians/">The Sumerians</a> (4100-1750BC) based around <a href="https://www.britannica.com/place/Mesopotamia-historical-region-Asia">Mesopotamia</a> (modern-day Iraq) calculated that the day was approximately 24 hours and that each hour was 60 minutes long. They used the Sun, stars and <a href="https://www.jstor.org/stable/41668444">water clocks to keep track of time</a>. <a href="https://www.britannica.com/technology/clepsydra">Water clocks</a> used the gradual flow of water from one container to another to measure time. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/556284/original/file-20231027-24-5tembs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/556284/original/file-20231027-24-5tembs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/556284/original/file-20231027-24-5tembs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/556284/original/file-20231027-24-5tembs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/556284/original/file-20231027-24-5tembs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/556284/original/file-20231027-24-5tembs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/556284/original/file-20231027-24-5tembs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/556284/original/file-20231027-24-5tembs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An ancient water clock from Persia.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Water_clock_zibad.JPG">Maahmaah</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The ancient Egyptians also <a href="https://www.britannica.com/topic/24-hour-clock">introduced a 24-hour time system</a> around 1550-1069BC. But the length of these “hours” varied depending on the time of year – longer in summertime than winter. These measures of time were based on the Sun, with 12 parts during daylight, and another 12 parts through the night. The Egyptians started using a sundial to represent this time system <a href="https://collection.sciencemuseumgroup.org.uk/objects/co473/ancient-egyptian-altitude-sundial-or-shadow-clock-in-pine-wood-sundial">around 1000-800BC</a>. Since sundials cannot tell the time at night, they used water clocks after dark. </p>
<p>In Europe, the development of time measurement gets a bit foggy over the centuries around AD700-1300AD, as all time-telling devices are <a href="https://wwnorton.com/books/9781324002932">bundled into the same Latin word, <em>Horologium</em></a>, in written European records.</p>
<p>The economist and historian David S. Landes claims in his book, <a href="https://www.hup.harvard.edu/catalog.php?isbn=9780674002821">Revolution in Time</a>, that monastic Christian prayers were more rigid compared with Judaism and Islam, using the heavens to dictate what time to pray across the Catholic church’s <a href="https://www.britannica.com/art/canonical-hours">seven set canonical hours</a>. For example, <a href="https://en.wikipedia.org/wiki/Sext#:%7E:text=Sext%2C%20or%20Sixth%20Hour%2C%20is,of%20the%20day%20after%20dawn.">sext</a> was supposed to be recited at midday. The time period between these canonical prayers became equal in length because of the rigidity of prayer times.</p>
<p>Timepieces may also have been more important in central Europe, because the cloudier weather would have made it harder to track the Sun and stars. </p>
<h2>Prayer time</h2>
<p>While we can’t be certain from historical records if it was monks who made the first mechanical clocks, we do know that they first appeared in the 14th century. </p>
<p>Their first mention is in the Italian physician, astronomer and mechanical engineer <a href="https://www.jstor.org/stable/1006002">Giovanni de Dondi’s treatise Tractatus Astrarii</a>, or Planetarium. De Dondi states that early clocks used gravity as their power source and were <a href="https://blogs.lse.ac.uk/businessreview/2016/09/27/mechanical-clocks-prove-the-importance-of-technology-for-economic-growth/">driven by weights</a>. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/556281/original/file-20231027-25-d5w849.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/556281/original/file-20231027-25-d5w849.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/556281/original/file-20231027-25-d5w849.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=761&fit=crop&dpr=1 600w, https://images.theconversation.com/files/556281/original/file-20231027-25-d5w849.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=761&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/556281/original/file-20231027-25-d5w849.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=761&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/556281/original/file-20231027-25-d5w849.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=956&fit=crop&dpr=1 754w, https://images.theconversation.com/files/556281/original/file-20231027-25-d5w849.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=956&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/556281/original/file-20231027-25-d5w849.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=956&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Drawing of the bottom section of De Dondi’s astronomical clock.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Giovanni_Di_Dondi_clock.png">Giovanni de Dondi</a></span>
</figcaption>
</figure>
<p>These weren’t the accurate clocks we see today – they probably kept time to within 15-30 minutes a day. These early clocks <a href="https://blogs.lse.ac.uk/businessreview/2016/09/27/mechanical-clocks-prove-the-importance-of-technology-for-economic-growth/">started popping up</a> in city centres but, since they did not have a face, they used bells to signal the hours. These signals began to organise the market times and administrative needs of each city. </p>
<p><a href="https://museum.seiko.co.jp/en/knowledge/MechanicalTimepieces02/">Coiled springs</a> as a method of releasing energy for clocks began to appear in Europe in the 15th century. This didn’t do anything to improve accuracy, but it could reduce the size of the clock. So, time became more of a personal as well as status object – you only have to look at <a href="https://www.bridgemanimages.com/en/victors-victoors/a-portrait-of-a-gentleman-pointing-to-a-pocket-watch-in-his-hand-1650-oil-on-canvas-pair-to-359446/oil-on-canvas/asset/359445">oil paintings</a> where subject’s watches are <a href="https://collection.barnesfoundation.org/objects/5779/Portrait-of-a-Man-Holding-a-Watch/">proudly displayed</a>. </p>
<p>The Dutch scientist <a href="https://www.sciencedirect.com/science/article/abs/pii/B978044450871350084X">Christian Huygens</a> first applied the pendulum to a clock in about 1656. This bolstered their accuracy to within 15 seconds a day, because each swing now took almost exactly the same time to complete.</p>
<p>As a result, time could be used more accurately in scientific observations, including of the stars. It also meant that clocks could now show an accurate minute hand.</p>
<h2>Time tracking in other parts of the world</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/556282/original/file-20231027-30-6tim3l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/556282/original/file-20231027-30-6tim3l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/556282/original/file-20231027-30-6tim3l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/556282/original/file-20231027-30-6tim3l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/556282/original/file-20231027-30-6tim3l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/556282/original/file-20231027-30-6tim3l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1006&fit=crop&dpr=1 754w, https://images.theconversation.com/files/556282/original/file-20231027-30-6tim3l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1006&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/556282/original/file-20231027-30-6tim3l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1006&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Model of the Antikythera mechanism.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:The_Antikythera_Mechanism_(3471978200).jpg">Tilemahos Efthimiadis/National Archaeological Museum, Athens</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Elsewhere in the world, some time-tracking devices date back many centuries earlier. In the 13th century, there is evidence of the use of gears to control the movement of components in <a href="https://www.hsm.ox.ac.uk/geared-astrolabe">Arabic astrolabes</a> – devices that could calculate time and help navigators determine their position. And long before that, the Ancient Greek <a href="https://www.britannica.com/topic/Antikythera-mechanism">Antikythera mechanism</a>, regarded as the world’s first computer, is dated at around 100BC (having been discovered in AD1901). These are both devices that predicted the motions of the planets. </p>
<p>Meanwhile in China, there was <a href="http://afe.easia.columbia.edu/songdynasty-module/tech-experiment.html#:%7E:text=The%20clock%20told%20not%20only,of%20the%20planets%20and%20stars.">Su Song’s astronomical clock</a> – dated to AD1088 – which was powered by water. So, while the clock was invented in Europe in the 14th century, Arabic and Chinese societies were far more technologically advanced at this time than their western Christian counterparts.</p>
<p>Today, wherever we are in the world, time is a unified construct – and the search for ever-more precise measurements continues. In 2021, scientists identified a new shortest timespan, <a href="https://www.snexplores.org/article/photon-journey-molecule-shortest-event-zeptosecond-physics#:%7E:text=Physicists%20have%20measured%20the%20shortest,Not%20familiar%20with%20zeptoseconds%3F">the zeptosecond</a>, which is how long it takes for a particle of light to pass through a molecule of hydrogen. </p>
<p>In modern society, time is usually organised to the minute or even second (think of train timetables, how we document transactions, or record setting in sports). This internalises within ourselves an obsession with being on time. People arrange to meet a friend, and hurry to the destination when they’re a minute or too late. But really, what’s a few minutes between friends?</p><img src="https://counter.theconversation.com/content/211978/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jaq Prendergast does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The 24-hour system was independently invented multiple times.Jaq Prendergast, Lecturer in Horology, Birmingham City UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1821972022-04-29T21:08:06Z2022-04-29T21:08:06ZStudents lead more public schools to close for Islamic holidays<figure><img src="https://images.theconversation.com/files/460582/original/file-20220429-14592-n08s9e.jpg?ixlib=rb-1.1.0&rect=11%2C22%2C7337%2C4880&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Several school districts across the country will close in observance of Eid, a holiday that marks the end of Ramadan.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/writing-in-a-notebook-royalty-free-image/871328144">FatCamera/E+ via Getty Images</a></span></figcaption></figure><p><em>Some public school districts across the nation will be closed on <a href="https://www.mtvernoncsd.org/site/default.aspx?PageType=3&DomainID=20&ModuleInstanceID=2255&ViewID=6446EE88-D30C-497E-9316-3F8874B3E108&RenderLoc=0&FlexDataID=10277&PageID=33">Monday, May 2, 2022</a>, or <a href="https://www.philasd.org/blog/2022/04/28/eidalfitr/#:%7E:text=On%20Tuesday%2C%20May%203rd%2C%202022,to%2Dsunset%20fasting%20of%20Ramadan.">Tuesday, May 3, 2022</a>, in observance of the Islamic holiday <a href="https://isna.net/month-of-ramadan/">Eid al-Fitr</a>, a festive celebration marking the end of the month of <a href="https://theconversation.com/what-ramadan-means-to-muslims-4-essential-reads-116629">Ramadan</a>, a month of fasting observed by Muslims worldwide. In the following Q&A, <a href="https://scholar.google.com/citations?user=COz6BG8AAAAJ&hl=en&oi=ao">Amaarah DeCuir</a>, an education researcher who specializes in issues of concern to Muslim students, illuminates some of the forces that are moving more school districts to close in observance of the Islamic holiday.</em></p>
<h2>How common is it for public schools to close for Islamic holidays?</h2>
<p>When New York City <a href="https://www.theguardian.com/us-news/2015/mar/04/new-york-city-muslim-holidays-public-schools">announced in 2015</a> that it would close its public schools in observance of Islam’s two most sacred holidays, it became the <a href="https://www.nytimes.com/2015/03/05/nyregion/new-york-to-add-two-muslim-holy-days-to-public-school-calendar.html">first big-city school district in the U.S. to do so</a>.</p>
<p>The New York City public school system is the <a href="https://nces.ed.gov/programs/digest/d19/tables/dt19_215.30.asp">largest in the nation</a>, and <a href="https://www.tc.columbia.edu/articles/2008/september/post-911-nyc-muslim-public-school-students-feel-safe-but-/#:%7E:text=About%20one%20in%2010%20students,included%20focus%20groups%20and%20ethnography.">about 10% of its student population</a> identifies as Muslim.</p>
<p>By the time New York City schools began to close for Eid, several smaller school districts had already been doing so for more than a decade. For instance, the Irvington school district in New Jersey <a href="https://www.religionnewsblog.com/5039/schools-slowly-adding-muslim-holiday-to-day-off-list">began to close for the Eid al-Fitr in 2003</a>.</p>
<p>In recent years, more and more school districts have begun to close in observance of Eid holidays. Those school districts include districts such as the <a href="https://www.thefreelibrary.com/Eid+made+holiday+in+Vermont+city+schools.-a0222678917">Burlington School District</a> in Vermont, which began to close for Eid al-Fitr in 2010, and <a href="https://www.freep.com/story/news/education/2019/04/20/detroit-schools-close-muslim-holiday-eid-al-fitr/3522641002/">Detroit</a>, which began to close its public schools for Eid holidays in 2019.</p>
<p>The list also includes <a href="https://www.philasd.org/blog/2022/04/28/eidalfitr/">Philadelphia</a>; <a href="https://p3cdn4static.sharpschool.com/UserFiles/Servers/Server_166764/File/BCPS%20Calendar%2021-22.pdf">Baltimore</a>; <a href="https://pgcmc.org/eid-ul-fitr-a-public-school-holiday-in-2021/">Prince George’s County in Maryland</a>; <a href="https://www.fcps.edu/calendars/standard-school-year-calendar/2021-22-school-year-calendar/2021-22-religious-and-cultural">Fairfax County</a>, <a href="https://loudounnow.com/2020/12/02/school-board-adds-4-holidays-for-next-school-year/">Loudoun County</a> and <a href="https://www.insidenova.com/headlines/prince-william-school-board-approves-2021-22-calendar-with-diverse-holidays/article_cbf29988-1f09-11eb-aa88-bfb26f06670a.html">Prince William County</a>, all in northern Virginia; and several districts across <a href="https://sahanjournal.com/education/minnesota-school-calendars-eid/">Minnesota</a>, which has a <a href="https://religionsmn.carleton.edu/exhibits/show/history-muslims/muslims-mn">sizable Muslim population</a>.</p>
<h2>Why take a day off if Muslims are a minority?</h2>
<p>In some cases, significant numbers of students were not coming to school on Eid al-Fitr anyway – and school officials began to take note. For instance, a school superintendent in Burlington, Vermont, once related that <a href="https://www.thefreelibrary.com/Eid+made+holiday+in+Vermont+city+schools.-a0222678917">about 75 of Burlington High School’s roughly 1,100 students were absent on Eid al-Fitr</a> in 2009 – about 25 more than on a typical school day. In the Fairfax County Public School system, reports show that <a href="https://www.fcps.edu/sites/default/files/media/forms/Absence%20Data%20Final3.pdf">33.3% and 38.5% more students than usual were absent from school</a> on Eid al-Fitr holidays in 2016 and 2017, respectively.</p>
<p>But absenteeism isn’t the only factor at play. Some school districts are beginning to observe Eid holidays as a matter of <a href="https://sahanjournal.com/education/minnesota-school-calendars-eid/">commitment to equal recognition</a> for Muslim families.</p>
<p>In the Hopkinton Public Schools, in Massachusetts, one school board leader noted that closing school for Eid holidays could <a href="https://www.metrowestdailynews.com/story/news/education/2022/02/05/hopkinton-schools-add-eid-lunar-new-year-no-school-holidays/6657230001/">attract a more diverse</a> pool of educators by not forcing them to take personal days to observe the holiday. In Detroit, a school leader said that closing for Eid holidays was a statement to celebrate the <a href="https://detroit.chalkbeat.org/2019/4/16/21107970/detroit-school-board-votes-to-close-schools-for-muslim-holiday-of-eid-al-fitr">diversity</a> of the community.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/zVbC4vmzeSI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Eid al-Fitr is celebrated by Muslims across the world.</span></figcaption>
</figure>
<h2>Who is leading efforts to get public schools to close for Eid?</h2>
<p>In many cases Muslim students are initiating efforts to gain support for schools to close for Eid al-Fitr. In Bridgeport, Connecticut, for instance, a <a href="https://longisland.news12.com/eid-al-fitr-to-become-official-school-holiday-in-bridgeport-schools-2023-24-school-year">group of eighth grade students in a civics class</a> got the school board to close schools for Eid al-Fitr. In Montclair, New Jersey, school officials decided to close for Eid as called for by a fifth grade Muslim girl’s <a href="https://patch.com/new-jersey/montclair/montclair-schools-will-observe-eid-holiday-after-girl-s-petition">online petition</a>. </p>
<p>In Iowa City, Iowa, a Muslim high school girl <a href="https://www.kcrg.com/2021/04/14/iowa-city-schools-to-take-days-off-for-muslim-and-jewish-holidays-following-student-led-campaign/">advocated</a> for over three years to promote the observance of Eid before the school system there decided to do so. And a student in Detroit helped persuade school board members there through an <a href="https://detroit.chalkbeat.org/2019/4/16/21107970/detroit-school-board-votes-to-close-schools-for-muslim-holiday-of-eid-al-fitr">op-ed</a> <a href="https://www.freep.com/story/opinion/contributors/2019/01/24/detroit-schools-eid-holidays/2639980002/">in the Detroit Free Press</a> to close in observance of Eid.</p>
<p>In some cases, such as in Baltimore, efforts to get public schools to close in observance of Eid have been described as a “<a href="https://www.nassp.org/publication/principal-leadership/volume-20/principal-leadership-april-2020/pins-and-posts-april-2020/">decadeslong battle</a>.” I predict that as more Muslim students call for public schools to close in observance of Eid, it won’t take nearly as long for additional schools to recognize the value of honoring Islamic holidays as other schools have done in recent years.</p>
<h2>What about calculating when the holidays begin?</h2>
<p>Since Muslims go by a <a href="https://islamonline.net/en/ramadan-and-the-lunar-calendar/">lunar calendar</a>, which is <a href="https://www.britannica.com/science/lunar-year">about 11 days shorter</a> than the 365-day solar calendar that most Americans use, the exact date of Eid al-Fitr changes from year to year.</p>
<p>And not everyone is in agreement about when a particular lunar month begins. Some Muslims go by <a href="https://fiqhcouncil.org/calendar/">astronomical calculations</a> to project the Islamic calendar well into the future. For instance, one Islamic calendar has <a href="https://fiqhcouncil.org/calendar/">projected specific Eid dates into the year 2045</a>. Other Muslims prefer to use traditional methods of local <a href="https://hilalcommittee.org/">moonsighting</a>, which involves using the naked eye to actually see the crescent of the moon to determine the start and end of a lunar month. </p>
<p>This partially explains why there could be different start and end dates for Ramadan on any given year that are <a href="https://www.forbes.com/sites/jamiecartereurope/2022/04/25/when-is-eid-al-fitr-2022-this-weekends-rare-shawwal-black-moon-will-end-ramadan-and-cause-a-risky-solar-eclipse-as-the-planets-align/?sh=2a06bd125b41">one day apart</a>. School district leaders may want to defer to whichever method is used by local Muslim authorities.</p><img src="https://counter.theconversation.com/content/182197/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Amaarah DeCuir does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>School districts throughout the nation are beginning to heed calls to give students and teachers a day off in observance of the Eid al Fitr, a major Islamic holiday held at the end of Ramadan.Amaarah DeCuir, Senior Professorial Lecturer in Education, American UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1707802021-12-30T19:15:48Z2021-12-30T19:15:48ZThe messy history of our modern, Western calendar<figure><img src="https://images.theconversation.com/files/436308/original/file-20211208-25-szsehi.jpeg?ixlib=rb-1.1.0&rect=126%2C69%2C3976%2C5478&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Wikimedia Commons</span></span></figcaption></figure><p>For something that’s meant to lend order to our lives, the modern Western calendar has <a href="https://global.oup.com/academic/product/scandalous-error-9780198799559?cc=jp&lang=en&">a messy history</a>. The mess, in part, comes about because of the difficulty of co-ordinating the orbits of celestial bodies with the cycles of day and night, and the passage of the seasons.</p>
<p>The year measured by the earth’s orbit around the sun is roughly an unruly 365.2422 days. The moon is likewise not a fan of whole numbers. In the space of a year, there are around 12.3683 lunar months. Societies have traditionally tried to make sure that the same seasons lined up with the same months. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/436001/original/file-20211207-17-12rf1tw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/436001/original/file-20211207-17-12rf1tw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436001/original/file-20211207-17-12rf1tw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436001/original/file-20211207-17-12rf1tw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436001/original/file-20211207-17-12rf1tw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436001/original/file-20211207-17-12rf1tw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436001/original/file-20211207-17-12rf1tw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436001/original/file-20211207-17-12rf1tw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The moon’s orbit around the earth cannot be properly measured in whole numbers.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p><a href="https://webspace.science.uu.nl/%7Egent0113/babylon/babycal.htm">Ancient calendars from Mesopotamia</a>, for example, co-ordinated months and seasons by adding extra months every now and then, a process called intercalation. In some lunar systems, though, the months can wander through the seasons – this is the case for the <a href="https://en.wikipedia.org/wiki/Islamic_calendar">Islamic Hijri calendar</a>.</p>
<p>The solar calendar of ancient Rome gives rise to our modern Western calendar. The Julian calendar, named after Julius Caesar’s reforms of 46/45 BCE, approximated the solar year to 365.25 days and inserted an extra day each four years. That left a rather annoying 11 and a bit minutes unaccounted for. More on those minutes later.</p>
<p>The Julian calendar also left us a legacy of months in strange positions. Our eleventh month, November, derives from the Latin for the number nine, a result of moving the start of the year from March to January. </p>
<p>New months and names were juggled and rejigged to match the mechanisms of power. August, for example, is named for the Emperor Augustus. As the <a href="https://press.princeton.edu/books/hardcover/9780691181653/time-and-power">great Australian historian Christopher Clark</a> has put it: “as gravity bends light, so power bends time”. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/wakey-wakey-a-history-of-alarm-clocks-and-the-mechanics-of-time-153716">Wakey wakey: a history of alarm clocks and the mechanics of time</a>
</strong>
</em>
</p>
<hr>
<h2>Christian time keeping</h2>
<p>As the Roman empire shifted into the world we now call the middle ages, the power that bent time most successfully was that of the church. But just as in the present, the church was a multiplicity of intersecting powers with local and regional differences, and with a variety of internal identities and struggles. The start of the year, for example, could vary widely across medieval societies.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/435997/original/file-20211207-133881-ife33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/435997/original/file-20211207-133881-ife33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/435997/original/file-20211207-133881-ife33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=969&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435997/original/file-20211207-133881-ife33l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=969&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435997/original/file-20211207-133881-ife33l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=969&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435997/original/file-20211207-133881-ife33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1217&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435997/original/file-20211207-133881-ife33l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1217&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435997/original/file-20211207-133881-ife33l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1217&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A manuscript from the calendar Très Riches Heures, reated between c. 1412 and 1416 for John, Duke of Berry, by the Limbourg brothers.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>Sometimes it was March 25, the day commemorating the appearance of the angel Gabriel to Mary. Other times it was December 25, the day agreed as Jesus’ birthday (the perfect 9-month gestation period). Sometimes, it was confusingly the moveable date of Easter, making years of changing length.</p>
<p>It was during this period that the problematic 11 and a bit minutes had their revenge. The seasons began to shift, little by little, and this had important implications for Christian time-keeping. </p>
<p>The date of Easter Sunday (another point of contention) was timed to follow the Northern Spring equinox, a natural symbol of light conquering darkness. But as that equinox began to slip back in time, a distinction started to emerge between a “legal” Easter – that decreed by the calendar – and a “natural” equinox, ie the equinox that could be observed. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/435996/original/file-20211207-25-1b2jjh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/435996/original/file-20211207-25-1b2jjh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435996/original/file-20211207-25-1b2jjh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=598&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435996/original/file-20211207-25-1b2jjh4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=598&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435996/original/file-20211207-25-1b2jjh4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=598&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435996/original/file-20211207-25-1b2jjh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=752&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435996/original/file-20211207-25-1b2jjh4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=752&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435996/original/file-20211207-25-1b2jjh4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=752&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Calendar of the dates of Easter, for the years 532–632 A.D. (Marble, in Museum of Ravenna Cathedral, Italy).</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>As the gap widened, scientists and theologians (often the same people) fought it out over proposals to reform the calendar. Should a number of days be omitted from the year, just once, to realign legal and observable time? If so, how many? And who should be in charge of the change?</p>
<p>The question became particularly intense in the 15th century with a number of calendar reform proposals failing the test of pragmatics or political backing from rulers across Europe. One such proposal was <a href="https://www.cornellpress.cornell.edu/book/9789462702448/peter-de-rivo-on-chronology-and-the-calendar/#bookTabs=1">discovered recently</a> hidden inside a printed book at the University Library in Cambridge. </p>
<p>It was written in 1488 by a theologian from the University of Louvain named Peter de Rivo and suggested 10 days be removed from the calendar. Peter thought that a celebration known as the jubilee, where crowds of pilgrims travelled from all over Europe to Rome would be the perfect time for making the reform known to the world. The proposal was not the first or last to sink like a stone.</p>
<p>But eventually those 10 days did disappear, when Pope Gregory reformed the calendar in 1582. This new calendar, the Gregorian calendar, jumped from 4 October 1582 to 15 October 1582. It also made a better approximation of the natural length of the year by manipulating leap years over a 400-year cycle.</p>
<p>The 1582 reform landed in a world rent by religious divisions, some old, some new. Protestant England did not adopt the changes till the 18th century. Many Orthodox Christian communities continued to follow the Julian calendar – with later revisions to that calendar proving contentious and provoking further schisms.</p>
<h2>Unreasonable nature</h2>
<p>It’s easy to feel lost in time. The calendar helps to give us a map to the shifting revolutions of the seasons, the shape of our lives, and the larger arcs of history. But while we are placed in the matrix of calendar time, we also make it: could we do better than the Gregorian calendar? </p>
<p>That question was asked with particular vehemence in the 18th century by so-called enlightened thinkers, and was brought to a head in the <a href="https://www.cambridge.org/core/books/calendar-in-revolutionary-france/219FFBFAD3C5D3CD9597779A8078BB27">French Revolution</a>. In 1793, the revolutionary government regularised the month to a standard 30 days (each with three weeks of ten days), leaving a messy five to six unallocated days a year, and giving workers only three days off each month. The start of the year was shifted to the autumn equinox, because an égalité (equality) of light and dark was a symbol of the new republic’s ideals.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/435998/original/file-20211207-141979-b6irqf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/435998/original/file-20211207-141979-b6irqf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435998/original/file-20211207-141979-b6irqf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=706&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435998/original/file-20211207-141979-b6irqf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=706&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435998/original/file-20211207-141979-b6irqf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=706&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435998/original/file-20211207-141979-b6irqf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=888&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435998/original/file-20211207-141979-b6irqf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=888&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435998/original/file-20211207-141979-b6irqf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=888&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">French Republican Calendar of 1794, drawn by Philibert-Louis Debucourt.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>The calendar was a victory of reason, if reason is aligned with simplicity, clarity and the number of our fingers. But, as we have seen, in astronomical terms nature is stubbornly unreasonable. The system was short-lived.</p>
<p>Part of the problem with calendar reform is that calendars have to do with our lived experiences of time, our habits, our rhythms, our memories. To make radical changes requires particular fervour (or megalomania).</p>
<p>But the history of calendars can also make us ask if we might modify our ordering of time in more gentle ways. This may not mean altering the calendar at a global or national level. But what about us here in our different regions of Australia? What if we finally acknowledged that <a href="http://www.bom.gov.au/iwk/">we don’t live with a four-season year</a>, adopting the far more interesting and attentive <a href="https://theconversation.com/explainer-the-seasonal-calendars-of-indigenous-australia-88471">seasonal calendars</a> developed by Indigenous cultures? </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-the-seasonal-calendars-of-indigenous-australia-88471">Explainer: the seasonal 'calendars' of Indigenous Australia</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/170780/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew S. Champion receives funding from the Australian Research Council (DE200101479 'The Sounds of Time' and DP210101623 'Albrecht Dürer's Material Worlds'). </span></em></p>The calendar helps to give us a map of the shifting revolutions of the seasons, ordering our days. But how did it come about?Matthew S. Champion, Senior Research Fellow in Medieval and Early Modern Studies, Australian Catholic UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1687192021-12-23T15:25:37Z2021-12-23T15:25:37ZHow common is the ‘Common Era?’ How A.D. and C.E. took over counting years<figure><img src="https://images.theconversation.com/files/438903/original/file-20211222-21-1jxt6bo.jpg?ixlib=rb-1.1.0&rect=53%2C0%2C3502%2C2338&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Amid the pandemic, confetti fell on an almost-empty Times Square last New Year's Eve.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/APTOPIXVirusOutbreakNewYorkNewYears/3d26a53371bc4f179aa4a3587b9d1f92/photo?Query=%22times%20square%22%20ball%20%22new%20year%27s%22&mediaType=photo&sortBy=arrivaldatetime:desc&dateRange=Anytime&totalCount=325&currentItemNo=10">AP Photo/Craig Ruttle</a></span></figcaption></figure><p>On Dec. 31, people from cultures all around the world will be raising a toast to welcome in A.D. 2023. Few of them will think about the fact that A.D. signals “anno Domini,” Latin for “in the year of our Lord.” In A.D. temporality – the one acknowledged by most societies today – next year marks 2024 years since the purported birth of Jesus Christ.</p>
<p>So why are we all toasting this new year, given that most of the world’s nearly 8 billion people aren’t Christians?</p>
<p>My fascination with time was nurtured by the millennium and the hype that surrounded its approach, as the globe anticipated traversing from 11:59 p.m., Dec. 31, 1999 to 12:00 a.m., Jan. 1, 2000. </p>
<p>Convinced that there was some truth to <a href="https://theconversation.com/if-you-think-the-millennium-bug-was-a-hoax-here-comes-a-history-lesson-129042">fears about technological disruptions caused by the Y2K bug</a>, I stayed away from <a href="https://timessquareball.net/ball-history/">the ball drop in Times Square</a>. Instead, I watched the celebration on my laptop and enjoyed trailing journalists’ reports abroad. I began to wonder: How did it come to be that people all over the Earth subscribed to – and were aware of – the temporal system followed by the Christian West? After all, cultures have historically experienced and documented time in a variety of ways. </p>
<p>These questions about time blossomed into <a href="https://www.press.umich.edu/11476655/the_medieval_postcolonial_jew_in_and_out_of_time">a research project and book</a>. Part of the phenomenon was caused by global capitalism, but I soon learned that another aspect involved the globalization of “anno Domini.” The A.D. system, often called “C.E.” or “Common Era” time today, was introduced in Europe during the Middle Ages. It <a href="https://muse.jhu.edu/article/540282/pdf">joined the world’s other temporal systems</a> like the Coptic, Seleucid, Egyptian, Jewish and the Zodiac calendars, along with calculations based on the years of rulers’ reigns and the founding of Rome. </p>
<p>Latin Christendom slowly but confidently came to dominate Europe, and its year dating system then came to dominate the world, so that most countries now take A.D. for granted, at least when it comes to globalized business and government. A.D.’s ubiquity has almost silenced other ways of thinking about time. This began during the medieval era, under the influence of educated Christian monks – what <a href="https://www.brepolsonline.net/doi/abs/10.1484/J.NMS.3.106?mobileUi=0">historian Bernard Gueneé</a> describes as “anno Domini’s” “conquest of time.”</p>
<p>My recent work as <a href="https://udayton.edu/directory/artssciences/english/krummel_miriamne.php">a medieval studies professor</a> focuses on the demonization of Jewish communities in Europe at a time when the A.D. system was gaining prominence and marginalizing the Jewish calendar.</p>
<h2>Counting backwards</h2>
<p>Part of <a href="https://www.press.umich.edu/11476655/the_medieval_postcolonial_jew_in_and_out_of_time">the story of “anno Domini” time</a> takes us back to the fourth and fifth century, when Christian scholars like <a href="https://overviewbible.com/eusebius/">Eusebius of Caesarea</a> and <a href="https://www.newworldencyclopedia.org/entry/John_Chrysostom">John Chrysostom</a> were trying to calculate what they considered was the beginning of Christian time – in other words, the birth date of Jesus of Nazareth. </p>
<p>Eusebius and Chrysostom were working with the Gospel accounts of Jesus’ birth and death. <a href="https://www.biblegateway.com/passage/?search=john+13&version=KJV">According to the Gospels</a>, Jesus was arrested around the time of the Jewish holiday of Passover, and the Gospel of John suggests that Jesus was about 33 when he died. Therefore, Eusebius and Chrysostom first tried to determine the date of his death based on Passover dates in the Jewish calendar. But <a href="https://brill.com/view/title/20608">both men failed in their calculations</a> and blamed the Jews for their difficulty. In their twisted reasoning, the Jewish community had postponed Passover in order to make “anno Domini” time impossible to calculate. This accusation illustrates the intense antisemitism common in Europe at their time and which work like theirs helped continue.</p>
<p>But in many ways, the real author of the world’s modern sense of time, the one who decided to choose the date when Year One would begin, is <a href="https://www.bl.uk/people/bede">the Venerable Bede</a>, an English monk who lived circa 673-735.</p>
<p>Bede found himself with several calculations he did not approve of, and decided Christ must have actually been born on <a href="https://brill.com/view/title/20608">Dec. 25, 1 B.C.</a>. By his reasoning, in other words, the A.D. system began the year after Jesus’ purported birth. Bede also determined that March 25, 34 A.D. marked Christ’s death. </p>
<figure class="align-center ">
<img alt="An open page from a medieval manuscript sits on a table." src="https://images.theconversation.com/files/438761/original/file-20211221-48250-ele5p9.jpg?ixlib=rb-1.1.0&rect=65%2C5%2C3245%2C2530&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/438761/original/file-20211221-48250-ele5p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=455&fit=crop&dpr=1 600w, https://images.theconversation.com/files/438761/original/file-20211221-48250-ele5p9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=455&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/438761/original/file-20211221-48250-ele5p9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=455&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/438761/original/file-20211221-48250-ele5p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=572&fit=crop&dpr=1 754w, https://images.theconversation.com/files/438761/original/file-20211221-48250-ele5p9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=572&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/438761/original/file-20211221-48250-ele5p9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=572&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/picture-shows-the-second-oldest-surviving-copy-of-the-news-photo/137304888?adppopup=true">Gavin Fogg/AFP via Getty Images</a></span>
</figcaption>
</figure>
<p>Bede, a monk in an important monastery in Northumbria, popularized the A.D. dating system by using it in his work “<a href="https://www.gutenberg.org/files/38326/38326-h/38326-h.html">Ecclesiastical History of the People of England</a>,” which made him the first historian to tell time by “anno Domini.” The “Ecclesiastical History” was dedicated to King Ceowulf of Northumbria, written in Latin in 731, and <a href="https://boydellandbrewer.com/9781843842736/the-old-english-version-of-bedes-ihistoria-ecclesiasticai/">translated into Old English</a> around the end of the ninth or the beginning of the 10th centuries. Still read by many today, it popularized “anno Domini” time by infusing A.D. time into events Bede told about the English people.</p>
<p>Taken together, these ingredients helped A.D. time become the norm. While the Christian calendar is built on and infused with other cultures’ time systems, A.D.’s popularization contributed to sidelining these calendars to the margins – what postcolonial scholars call “<a href="https://www.routledge.com/The-Location-of-Culture/Bhabha/p/book/9780415336390">temporal colonization</a>.”
For example, the date Bede set for Easter in his work “<a href="https://www.google.com/books/edition/Bede_The_Reckoning_of_Time/yFsw-Vaup6sC?hl=en">The Reckoning of Time</a>” is based on a polytheistic celebration of Eostre, a German goddess. Eostre has, thus, disappeared into Easter.</p>
<p>Likewise, the fraught connections between the dates of Jesus’s Passion, Easter and Passover <a href="https://www.press.umich.edu/11476655/the_medieval_postcolonial_jew_in_and_out_of_time">further fueled antisemitism</a> at a time when Jewish communities were also trying to <a href="https://www.hup.harvard.edu/catalog.php?isbn=9780674052543">formalize a Jewish calendar</a>.</p>
<figure class="align-right ">
<img alt="A medieval manuscript shows a man climbing a ladder while holding an hourglass." src="https://images.theconversation.com/files/438747/original/file-20211221-27-1g5q4mm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/438747/original/file-20211221-27-1g5q4mm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=712&fit=crop&dpr=1 600w, https://images.theconversation.com/files/438747/original/file-20211221-27-1g5q4mm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=712&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/438747/original/file-20211221-27-1g5q4mm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=712&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/438747/original/file-20211221-27-1g5q4mm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=895&fit=crop&dpr=1 754w, https://images.theconversation.com/files/438747/original/file-20211221-27-1g5q4mm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=895&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/438747/original/file-20211221-27-1g5q4mm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=895&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A medieval Jewish manuscript containing</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/e-codices/17153075610/in/photolist-s8KZLW-dEHAw1-NSfjHt-9b4kFv-9gCU5z-qejZbN-bBzLSy-dF1RjG-cMXmyh-rAz7bh-fmLQVc-rernwT-bBzJX3-dEHyFw-rRUNdk-7be69Q-dEC9C4-cMXeEd-dEHzEy-dEHzsb-dNakEN-7baHmM-9ZVHfu-dAg8u7-dBPcxQ-dBPbmC-dEHxgy-BFCpEt-dmFqZA-rerjJt-8UyZU6-ezp7dB-s8SNhD-5CJAtV-rRUVW6-LwG5nP-fxiLmL-fFibFb-9b6QcJ-2i73vxA-reeAgf-sbbyYi-bV6ZLo-rerf9X-bBzHE5-fxiR23-7Hy4RR-rTDmK5-7Hy4Pn-rTDrjW/">e-codices/Zürich, Braginsky Collection/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Changing the name</h2>
<p>Approximately 1,400 years ago, when Bede selected <a href="https://books.google.com/books?id=UuT607E79KIC&pg=PA69&source=gbs_toc_r&cad=3#v=onepage&q&f=false">a date to begin “anno Domini” time</a>, he perhaps unwittingly started the process of privileging Christian time, which is now near-universally recognized.</p>
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<p>Today, many people use the expressions “common era” and “before the common era,” or C.E. and B.C.E., instead of A.D. and B.C. But despite what we call it now, the roots of this system are not “common” but Christian. As the medieval studies scholar <a href="https://www.upenn.edu/pennpress/book/14437.html">Kathleen Davis</a> writes, using C.E. “does little to diminish the effect of a globalized Christian calendar.”</p>
<p>Initially, I too had applauded C.E. as a less Christian replacement for A.D. But today, I’d argue it is just the equivalent of a yellow sticky note <a href="https://www.upenn.edu/pennpress/book/14437.html">placed over it</a>. There’s nothing naturally “common” about the “common era,” and it’s worth applauding all kinds of diversity – even in time – on planet Earth. This year, what will you be toasting at 11:59 p.m. on Dec. 31?</p><img src="https://counter.theconversation.com/content/168719/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Miriamne Ara Krummel does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Today most societies take the A.D. time system for granted. That wasn’t always the case.Miriamne Ara Krummel, Professor of English, University of DaytonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1135582019-04-08T03:26:53Z2019-04-08T03:26:53ZCurious Kids: how did the months get their names?<figure><img src="https://images.theconversation.com/files/265784/original/file-20190326-36264-4orrbi.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3799%2C2508&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In the very beginning of the Roman calendar (more than 2000 years ago), there were only 10 months in the year.</span> <span class="attribution"><span class="source">Jule Berlin/Shutterstock</span></span></figcaption></figure><p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
<hr>
<blockquote>
<p><strong>How did the months get their names? - Sylvie, age 8, Brisbane.</strong> </p>
</blockquote>
<hr>
<p>The names of the months are very old and they come from ancient Rome. Rome is the capital of Italy and several thousand years ago it was the heart of a very powerful empire (which is like a kingdom, only bigger). </p>
<p>In the very beginning of the Roman calendar (more than 2000 years ago), there were only 10 months in the year. The Romans based this version on the ancient Greek calendar. Later, however, the Romans added in two more. The names of some of the months also changed a few times.</p>
<p>Here’s how the early version would have looked.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/266955/original/file-20190401-177193-pa58ty.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266955/original/file-20190401-177193-pa58ty.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/266955/original/file-20190401-177193-pa58ty.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=947&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266955/original/file-20190401-177193-pa58ty.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=947&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266955/original/file-20190401-177193-pa58ty.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=947&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266955/original/file-20190401-177193-pa58ty.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1190&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266955/original/file-20190401-177193-pa58ty.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1190&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266955/original/file-20190401-177193-pa58ty.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1190&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This fancy fellow is Mars, the Roman god of war. March is named after him.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>In the early days</h2>
<p>MARCH: Happy New Year! March was the start of the year for the Romans. The beginning of spring was the time when everyone could go out and start fighting each other, so the month was named after Mars – the Roman god of war.</p>
<p>APRIL: The name for this month may come from a Roman word for “second” – aprilis – as it was the second month of the Roman year.</p>
<p>MAY: Spring is in full bloom for the Romans in May, and this month is named after Maia – a goddess of growing plants.</p>
<p>JUNE: This month is named after Juno, the queen of the Roman gods.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/266961/original/file-20190401-177187-1vmzp0p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266961/original/file-20190401-177187-1vmzp0p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/266961/original/file-20190401-177187-1vmzp0p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=437&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266961/original/file-20190401-177187-1vmzp0p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=437&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266961/original/file-20190401-177187-1vmzp0p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=437&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266961/original/file-20190401-177187-1vmzp0p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=549&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266961/original/file-20190401-177187-1vmzp0p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=549&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266961/original/file-20190401-177187-1vmzp0p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=549&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Here’s a statue of Juno, the Roman queen of the gods. June is named after her.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>JULY: This month used to be called Quintilis – the Roman word for “fifth” as it was the fifth month of the Roman year. It was later changed to July by the ruler of Roman world, Julius Caesar, after his family name (Julius).</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/266966/original/file-20190401-177175-ruviir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266966/original/file-20190401-177175-ruviir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/266966/original/file-20190401-177175-ruviir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266966/original/file-20190401-177175-ruviir.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266966/original/file-20190401-177175-ruviir.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266966/original/file-20190401-177175-ruviir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266966/original/file-20190401-177175-ruviir.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266966/original/file-20190401-177175-ruviir.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Here’s the Roman leader Julius Caesar, who decided to name a month after his family name (Julius). He called it July.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>AUGUST: This month was first called Sextillia – the Roman word for “sixth”, as it was the sixth month of the Roman year. It was later changed to August by the Emperor Augustus, and he named it after himself.</p>
<p>SEPTEMBER: The name for this month comes from the Roman word for “seventh” – septimus – as it was the seventh month of the Roman year.</p>
<p>OCTOBER: The name for this month comes from the Roman word for “eighth” - octavus - as it was the eighth month of the Roman year.</p>
<p>NOVEMBER: The name for this month comes from the Roman word for “ninth” – nonus – as it was the ninth month of the Roman year.</p>
<p>DECEMBER: The name for this month comes from the Roman word for “tenth” – decimus – as it was the tenth month of the Roman year.</p>
<h2>Then a few extra months were added…</h2>
<p>JANUARY: This was one of the extra months that the Romans added to the year. This month was named after Janus – the god of beginnings and endings. He is often depicted as having two faces.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/266968/original/file-20190401-177181-ojgcf0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266968/original/file-20190401-177181-ojgcf0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/266968/original/file-20190401-177181-ojgcf0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266968/original/file-20190401-177181-ojgcf0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266968/original/file-20190401-177181-ojgcf0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266968/original/file-20190401-177181-ojgcf0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266968/original/file-20190401-177181-ojgcf0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266968/original/file-20190401-177181-ojgcf0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Janus, the god of beginning and endings, is often shown as having two faces.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/w/index.php?curid=7404342">By Loudon dodd - Own work, CC BY-SA 3.0</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>FEBRUARY: This is another extra month that the Romans added to the calendar. They put it right after January. Its name comes from a festival that was held at this time called Februa. The festival aimed to cleanse the city of evil spirits and welcome health and fertility.</p>
<p>Because the Romans put two new months into the year, the names of the months do not make sense anymore. If our year started in March as it did for the Romans, December would still be the tenth month. </p>
<p>But 450 years ago, people who used this calendar started thinking that January was the first month of the year. So now December in the twelfth month for the Western calendar. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-are-there-different-seasons-at-specific-times-of-the-year-109380">Curious Kids: why are there different seasons at specific times of the year?</a>
</strong>
</em>
</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em></p>
<hr>
<p><em>An earlier version of this article incorrectly described Julius Caesar as an emperor instead of the ruler of the Roman world. It also said the lead picture showed Caesar, instead of Augustus. These errors were introduced in the editing process and have now been corrected.</em></p><img src="https://counter.theconversation.com/content/113558/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Matthew does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>December is named for the Roman word for “tenth”. So, why is it the twelfth month?Chris Matthew, Lecturer in Ancient History, Australian Catholic UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/941082018-04-12T19:56:15Z2018-04-12T19:56:15ZOn Friday the 13th, leave the superstitions at home<figure><img src="https://images.theconversation.com/files/214390/original/file-20180411-587-u6xrpt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock.com</span></span></figcaption></figure><p>Of all the days to stay in bed, Friday the 13th is surely the best. It’s the title of a popular (if increasingly corny) horror movie series; it’s associated with bad luck and it’s generally thought to be a good time not to take any serious risks. </p>
<p>Even if you try to escape it, you might fail, as happened to New Yorker Daz Baxter. On Friday 13th in 1976, he decided to just stay in bed for the day, only to be killed when the floor of his apartment block collapsed under him. There’s even a term for the terror the day evokes: <a href="https://www.macmillandictionary.com/buzzword/entries/paraskevidekatriaphobia.html">Paraskevidekatriaphobia</a> was coined by the psychotherapist <a href="http://www.drdossey.com/Bio.htm">Donald Dossey</a>, a specialist in phobias, to describe an intense and irrational fear of the date. </p>
<p>Unfortunately there is always <a href="http://ed5015.tripod.com/PaFriday13thCalendar11.htm">one Friday 13th in a year</a>, and sometimes there are as many as three. Today is one of them - and another comes in July. But no matter how many times the masked killer <a href="http://en.wikipedia.org/wiki/Jason_Voorhees">Jason Voorhees</a> from <a href="http://www.imdb.com/title/tt0080761/?ref_=nv_sr_2">Friday the 13th</a> returns to haunt our screens, this fear is in our own minds rather than any basis in science. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/bcoi-Zgg8BU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>One study did show a small rise in accidents on that day for women drivers in Finland, <a href="https://www.ncbi.nlm.nih.gov/pubmed/12450968">but much of the problem was due to anxiety rather than general bad luck.</a> Follow-up <a href="https://translate.google.com.au/translate?hl=en&sl=de&u=http://www.skeptizismus.de/freitag.pdf&prev=search">research</a> found no consistent evidence of a <a href="https://www.ncbi.nlm.nih.gov/pubmed/15546493">rise in accidents</a> on the day, but suggested that if you’re superstitious, it might be better not get behind the wheel of a car on it anyway.</p>
<p>The stigma against Friday 13th likely comes from a merging of two different superstitions. In the <a href="http://www.jstor.org/stable/i266158">Christian tradition</a>, the death of Jesus took place on a Friday, following the presence of 13 people at the Last Supper. In Teutonic legend, the god Loki appears at a dinner party seated for 12 gods, making him the outcast 13th at the table, <a href="https://www.csicop.org/superstition/library/number_thirteen">leading to the death of another guest</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214387/original/file-20180411-584-1y17nwe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214387/original/file-20180411-584-1y17nwe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214387/original/file-20180411-584-1y17nwe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214387/original/file-20180411-584-1y17nwe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214387/original/file-20180411-584-1y17nwe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214387/original/file-20180411-584-1y17nwe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214387/original/file-20180411-584-1y17nwe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214387/original/file-20180411-584-1y17nwe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">13 was certainly unlucky number for Jesus. Leonardo da Vinci, The Last Supper, 1498.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:%C3%9Altima_Cena_-_Da_Vinci_5.jpg">Wikimedia</a></span>
</figcaption>
</figure>
<p>Elsewhere in the world, 13 is less unlucky. In Hinduism, people fast to worship Lord Shiva and Parvati on <em>Trayodashi</em>, the 13th day in Hindu month. There are 13 Buddhas in the Shingon sect of Buddhism, and there is mention of a lucky 13 signs, rather than unlucky, in <a href="https://www.amazon.com/Origins-Popular-Superstitions-Customs-Forgotten/dp/1605064580">The Tibetan Book of the Great Liberation</a>.</p>
<p>In Italy, it is more likely to be “heptadecaphobia”, or <a href="https://www.researchgate.net/publication/311337579_Superstitions_religiosity_and_secularization_An_analysis_of_the_periodic_oscillations_of_weddings_in_Italy">fear of the number 17</a>, that leads to a change of plans. In Greece, Spain, and Mexico, the “unlucky” day is not Friday 13th, but Tuesday 13th. </p>
<p>In China, the number four is considered significantly unlucky, as it is nearly homophonous to the word “death”. In a <a href="http://www.mccrindle.com.au/ResearchSummaries/The-Lucky-Country.pdf">multicultural country like Australia</a> you may find hotels and cinemas missing both 13th and fourth floors, out of respect for the trepidation people can have about those numbers.</p>
<h2>The lure of superstition</h2>
<p>Superstitions were one of the first elements of paranormal beliefs studied in the early 1900s. While many are now just social customs rather than a genuine conviction, their persistence is remarkable.</p>
<p>If you cross your fingers, feel alarmed at breaking a mirror, find a “lucky” horseshoe or throw spilled salt over your shoulder, you are engaging in long-held practices that can have a powerful impact on your emotions. Likewise, many students are now heading towards their semester exams. In the lecture rooms, they may take lucky charms such as a particular pen or favourite socks. </p>
<p>In sports, baseballer Nomar Garciaparra is known for his <a href="https://www.youtube.com/watch?v=WIJYdE2Juew">elaborate batting ritual</a>. Other sports people wear “lucky gear” or put on their <a href="https://www.amazon.com/Rituals-Ceremonies-Popular-Culture-Browne/dp/0879721618">gloves in a particular order</a>. The great cricket umpire David Shepherd stood on one leg <a href="https://www.thenational.ae/uae/an-umpire-with-the-air-of-a-genial-butcher-1.491740">whenever the score reached 111</a>. These sorts of superstitions are humorously depicted in the film <a href="http://www.imdb.com/title/tt1045658/">Silver Linings Playbook</a>. It’s interesting to note that it’s often the <a href="https://global.oup.com/academic/product/believing-in-magic-9780199996926?cc=au&lang=en&">successful athletes</a> who have these superstitions and stick to them.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214394/original/file-20180411-543-1i31vnq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214394/original/file-20180411-543-1i31vnq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214394/original/file-20180411-543-1i31vnq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214394/original/file-20180411-543-1i31vnq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214394/original/file-20180411-543-1i31vnq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214394/original/file-20180411-543-1i31vnq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214394/original/file-20180411-543-1i31vnq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214394/original/file-20180411-543-1i31vnq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Lucky charms can make you feel good.</span>
<span class="attribution"><span class="source">Shutterstock.com</span></span>
</figcaption>
</figure>
<p>One key reason for the persistence of superstition is a psychological concept called a “discriminative stimulus”. An example of this is the gambler who notices he always seem to win when betting on “lucky 7”, and forgets all the times that same number has not been in his favour.</p>
<p>Charms do work in a fashion. If you wear your lucky underwear and succeed enough, you will feel distress that actually impedes your performance if you’re not wearing them. This then influences your performance – an “A” seems guaranteed because you walk in fully prepared. </p>
<p>But if you’re feeling a little anxious this Friday, try to remember there’s nothing different about it to any other day.</p><img src="https://counter.theconversation.com/content/94108/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kylie Sturgess does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Superstition holds that Friday 13th is the day to stay in bed and avoid taking risks. But it’s all in our heads.Kylie Sturgess, Tutor and Researcher Radio Broadcasting, Murdoch UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/884712018-01-02T20:51:05Z2018-01-02T20:51:05ZExplainer: the seasonal ‘calendars’ of Indigenous Australia<figure><img src="https://images.theconversation.com/files/200318/original/file-20171221-17712-1iuedf4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Lalin in Western Australia is 'married turtle season'.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/briangratwicke/8502138614/in/photolist-Kw34hz-dXiFAN-96dJdc-cXCZ5E-c8kCoy-7jr7v2-c8kCaC-c8kCzu-Q1ifn3-qdawn8-qSENnr-R4sgi5-R4siiC-aVqqKz-7TybSE-5uNEcd-c8kCFG-5uJfYR-c8kCk9-5uJfcn-5uJey4-5uJgdX-eAKBU6-5uJ7Rt-7fTDiA-7ZXDzt-e9stnn-qA6tdu-8fjmzc-oUJxS-CpTMsZ-CNMrXg-msCwjo-7rzra9-8fjje6-8fjhxk-8fjjLg-8fnB6E-8fnx8A-8fniK9-upEP2E-QfinGv-8fnhVQ-8fnkQd-8fjiGx-8fnz4N-8fj5cv-8fnk3d-8fnjx3-UHpNat">Brian Gratwicke/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>On Wangkumarra land, in the corner-country near the borders of Queensland, New South Wales and South Australia, stands an ancient stone arrangement. It has been placed to the side of a huge complex, rivalling Stonehenge, featuring megaliths polished, carved and placed to balance precariously on each other. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/200301/original/file-20171221-5004-1tr530f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/200301/original/file-20171221-5004-1tr530f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/200301/original/file-20171221-5004-1tr530f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/200301/original/file-20171221-5004-1tr530f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/200301/original/file-20171221-5004-1tr530f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/200301/original/file-20171221-5004-1tr530f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/200301/original/file-20171221-5004-1tr530f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/200301/original/file-20171221-5004-1tr530f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ancient stone arrangements on Wangkumarra land.</span>
<span class="attribution"><span class="source">Tyson Yunkaporta</span></span>
</figcaption>
</figure>
<p>They should fall, but they don’t, as this is a place where time runs differently. In contrast to the Western “arrow of time”, the small rock formation pictured shows the non-linear, infinitely interconnected cycle of time followed by the First People who built the site and used it over millennia. It is a stone calendar, aligned within a fraction of a millimetre to the points of the compass.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/200302/original/file-20171221-4973-1pd5nfl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/200302/original/file-20171221-4973-1pd5nfl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/200302/original/file-20171221-4973-1pd5nfl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/200302/original/file-20171221-4973-1pd5nfl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/200302/original/file-20171221-4973-1pd5nfl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/200302/original/file-20171221-4973-1pd5nfl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/200302/original/file-20171221-4973-1pd5nfl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/200302/original/file-20171221-4973-1pd5nfl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The stone calendar on Wangkumarra land.</span>
<span class="attribution"><span class="source">Tyson Yunkaporta</span></span>
</figcaption>
</figure>
<p>The key to understanding this temporal reality is the shape of the stone calendar. It is round, not a continuum. There is no beginning or end, and as such, there is no “New Year”. Seasons do not serve as a basis for linear metaphors of new life in spring to death in winter. </p>
<p>Instead, both seasons and humans are viewed as components of cycles. Around Australia, Indigenous languages vary in both the number of season words in their lexicon and their precise meaning. This is at least partly due to the very different kinds of weather experienced around the year in different parts of the country.</p>
<h2>A tour of the seasons</h2>
<p>In the Tiwi islands just to the north of Darwin there are three major <a href="https://www.csiro.au/en/Research/Environment/Land-management/Indigenous/Indigenous-calendars/Tiwi">seasons named in the Tiwi language</a>: <em>Kumunupunari</em> (the dry season of fire and smoke); <em>Tiyari</em> (the season of hot, humid weather); and <em>Jamutakari</em> (the wet season of daily rain and full rivers). These three seasons subsume 13 overlapping, more precisely defined seasons. </p>
<p>For example, in the <em>Mumpikari</em> season (which overlaps with the start of the <em>Jamutakari</em> “wet season”) the first rains after the dry time make the ground soft and muddy enough to retain the footprints left by possums returning to their trees, which makes the possums easier to track when hunting. </p>
<p>Understanding the meaning of a word like <em>Mumpikari</em> “season of muddy possum tracks” entails knowledge of the type of weather experienced at that time (first rains following a long dry spell), consequent changes in the local ecology (muddy ground), as well as changes in human behaviour and potential sources of food (it’s a good time to hunt and eat possums).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/200091/original/file-20171220-4968-17ox669.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/200091/original/file-20171220-4968-17ox669.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/200091/original/file-20171220-4968-17ox669.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/200091/original/file-20171220-4968-17ox669.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/200091/original/file-20171220-4968-17ox669.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/200091/original/file-20171220-4968-17ox669.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/200091/original/file-20171220-4968-17ox669.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/200091/original/file-20171220-4968-17ox669.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In the Tiwi Islands Mumpikari is ‘season of muddy possum tracks’</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/51035796522@N01/150925285/in/photolist-ekwQ6-SKkj-SKkL-72dBT-eeK48M-eeJBoR-72dcK-72dKT-72dto-72dPN-72dqr-6w4Ejk-72dTo-6mjVth-2NeiBY-72e8c-72dZ1-4dFoRB-72diZ-72e46-72dH2-NfBwXE-9kSxGT-9kSxHM-65TRn5-9kSxHn-9XQwfy-qVaHDu-cJ18g9-72dFw-nzqtcz-7qTrau-aM2UPM-pWbtnQ-8ND8y-5ZN82h-AFSZi-Covjzv-R4TvU-mYHXLM-7Fjwcs-CMoX5r-SKkB-AFUYd-PUHLBa-N7Lmv7-NA6L5A-PJv1Dk-PFTa5o-PJv8k6">Marcia Cirillo/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>The changes in weather, ecology and potential food sources over the course of the year are dramatic, but vary significantly across a continent as large as Australia. The season experienced in tropical Cape York in January is very different to January in Tasmania. Likewise, the middle of the year brings radically different weather patterns to the tropical north, temperate south and central desert regions respectively. </p>
<p>The definitions of seasonal terms tell us a lot about the ecology that a language is spoken within and how speakers interact with it. In the <a href="http://ausil.org/Dictionary/Warlpiri/lexicon/index.htm">Warlpiri language</a> of the Tanami Desert, for example, several seasonal terms (such as <em>karapurda</em>) make reference to the prominent westerly winds that blow at the onset of the hot season.</p>
<p>Common food sources also feature prominently in the definitions of season terms, such as <em>mangkajingi</em>, “season of year when goannas are easily found in shallow burrows”. In the <a href="https://www.degruyter.com/view/product/181100">Bardi language</a> of the Dampier Peninsula (WA), the build up to the wet season is named <em>Lalin</em> and colloquially referred to as “married turtle season”, because the mating turtles are a prized food source at this time.</p>
<p>In Gulumoerrgin (Larrakia) language group, spoken around Darwin, the year is divided into <a href="https://www.csiro.au/en/Research/Environment/Land-management/Indigenous/Indigenous-calendars/Gulumoerrgin">seven named seasons</a>. Each of these seasons is associated with distinctive patterns of weather, but also changes in flora, fauna, and human activity. The <em>Gurrulwa</em> season, or “big wind time”, is heralded by the flowering of wattles, which in turn indicates that the local stingrays are plentiful and good to eat. The flowering of the Yellow Kapok at this time in turn indicates that it is the time for important traditional ceremonies to be held. </p>
<h2>Connections</h2>
<p>These connections between species are often cemented in language by using a single word. In the <a href="http://link.aiatsis.gov.au/portal/A-first-dictionary-of-Dalabon-Ngalkbon/BBBUofEV2CM/">Dalabon language</a> of Arnhem land, the word <em>yawok</em> has <a href="http://www.elpublishing.org/docs/6/01/LLS-Chapter-15-Cutfield.pdf">two meanings</a>: (1) a species of yam (<em>Dioscorea bulbifera</em>); and (2) a species of grasshopper (<em>Caedicia spp.</em>). To the untrained observer, the yam and grasshopper might appear to have little in common. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/200094/original/file-20171220-4951-19uy81t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/200094/original/file-20171220-4951-19uy81t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/200094/original/file-20171220-4951-19uy81t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/200094/original/file-20171220-4951-19uy81t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/200094/original/file-20171220-4951-19uy81t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/200094/original/file-20171220-4951-19uy81t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/200094/original/file-20171220-4951-19uy81t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/200094/original/file-20171220-4951-19uy81t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In Arnhem Land, when the yawok (grasshopper) calls, the yawok (yams) are ready for harvesting.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Caedicia_simplex_1.jpg">Wikimedia/JJ Harrison</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>But for Dalabon speakers, this naming practice is a useful mnemonic that helps them remember that the yam is ripe for harvest precisely at that time of year when the grasshopper’s mating call can be heard. <a href="http://glottolog.org/resource/reference/id/178184">Similar principles</a> have been found to underpin the naming of plant and animal species in languages such as Bininj Gun-Wok and Ndjébbana.</p>
<p>The words of any language tell us a lot about the history of its speakers; who they’ve been in contact with, where and how they have lived. This is certainly true of the English calendar months. It is also seen in the number and nature of the seasons named by different Indigenous communities, from the tropical north of Australia to the chillier climates down south. </p>
<p>With around 370 languages and many hundreds more dialects originally spoken in Australia, it is impossible to do justice to the wealth and variety of traditional systems of tracking time and seasons. But a recurrent theme is the interconnectedness of human activities and the cycle of changes in flora and fauna that attend the tilting of the earth’s axis.</p><img src="https://counter.theconversation.com/content/88471/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alice Gaby receives funding from the Australian Research Council. She is a member of the Resource Network for Linguistic Diversity's executive committee, and of the Victorian State Government's Geographic Place Names Advisory Committee. </span></em></p><p class="fine-print"><em><span>Tyson Yunkaporta does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>On Wangkumarra land, in the corner-country near the borders of Queensland, New South Wales and South Australia, stands an ancient stone arrangement. It has been placed to the side of a huge complex, rivalling…Alice Gaby, Senior Lecturer in Linguistics, Monash UniversityTyson Yunkaporta, Senior Lecturer Health, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/572472016-04-05T11:25:12Z2016-04-05T11:25:12ZWhy the UK tax year begins on April 6 (it’s a very strange tale)<figure><img src="https://images.theconversation.com/files/117345/original/image-20160404-27112-1dklf74.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">shutterstock.com</span></span></figcaption></figure><p>You might think, logically, that the beginning of the tax year would coincide with the calendar year – and in some countries it does. In the UK, however, the scramble to get your affairs in order comes to its conclusion on April 5, with the new tax year starting on April 6. To understand the reason for this apparently random date, you have to go back to medieval times. </p>
<p>In England and Ireland, the New Year used to start on March 25, also known as “Lady Day” in commemoration of the angel Gabriel’s announcement to the Virgin Mary that she would become the mother of Jesus Christ. Along with Midsummer on June 24, Michaelmas on September 29, and Christmas Day on December 25, Lady Day was one of the four most important days in the religious calendar. All accounts, including debts and rents, had to be settled by these so-called “quarter days”, and Lady Day was the first, gradually becoming regarded as the start of the financial year (although the precise reason for this remains unknown). </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/117479/original/image-20160405-13557-kfcjme.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/117479/original/image-20160405-13557-kfcjme.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=794&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117479/original/image-20160405-13557-kfcjme.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=794&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117479/original/image-20160405-13557-kfcjme.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=794&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117479/original/image-20160405-13557-kfcjme.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=998&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117479/original/image-20160405-13557-kfcjme.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=998&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117479/original/image-20160405-13557-kfcjme.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=998&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Lady Day.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/Nativity#/media/File:Bartolom%C3%A9_Esteban_Perez_Murillo_023.jpg">The Yorck Project</a></span>
</figcaption>
</figure>
<p>The move forward to April 6 results from changes to the calendar and the actual number of days in various years. Until 1582, Europe had used the Julian calendar established by Julius Caesar. Under the Julian calendar, the year had 11 months of 30 or 31 days, with one month, February, consisting usually of 28 days but with 29 every fourth or “leap” year. This had worked well for centuries, but because it did not align exactly with the solar calendar (the time it takes for the Earth to move round the sun), over time problems developed. </p>
<h2>Playing catch-up</h2>
<p>The Julian year was only 11½ minutes longer than a solar year, but by the late 1500s, this had all added up and the Julian calendar was some ten days adrift from the solar calendar. The Roman Catholic church was especially concerned because the celebration of Easter had been gradually getting later than when it had been celebrated by the early church. </p>
<p>And so in October 1582 Pope Gregory XIII instituted a change (to the “Gregorian” calendar) to solve the problem: three leap days were omitted every 400 years by the authority of a papal bull <a href="http://www.bluewaterarts.com/calendar/NewInterGravissimas.htm">known as “Inter Gravissimas”</a>. While Europe adopted the Gregorian calendar, however, England, with its history of conflict with the Roman Catholic church, did not (nor did Russia), and <a href="http://www.nationalarchives.gov.uk/palaeography/quick_reference.htm">continued with the Julian calendar</a>.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/117327/original/image-20160404-27129-ifqjn8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/117327/original/image-20160404-27129-ifqjn8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=602&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117327/original/image-20160404-27129-ifqjn8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=602&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117327/original/image-20160404-27129-ifqjn8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=602&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117327/original/image-20160404-27129-ifqjn8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=757&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117327/original/image-20160404-27129-ifqjn8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=757&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117327/original/image-20160404-27129-ifqjn8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=757&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Gregorian Calendar.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/d/d8/DBP_1982_1155_400_Jahre_Gregorianischer_Kalender.jpg">Cropped from Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>By 1752, when it was 11 days out of alignment with the rest of Europe, England finally accepted that it would have to make a change. The decision was made to drop 11 days from the month of September to catch up, and so September 2 was followed by September 14 that year. To ensure that there was no loss of tax revenues, however, the Treasury extended the 1752 tax year by adding on the 11 days at the end. Consequently, the beginning of the 1753 tax year was moved to April 5. </p>
<p>In 1800 a further adjustment was made, shifting the start of the tax year forward by one more day to April 6, once again to mitigate for the differences between the Julian and Gregorian calendars. The year 1800 would have been a leap year under the Julian calendar system, but not the Gregorian one, so the Treasury treated 1800 as a leap year for purposes of taxation to get an extra day’s revenue. April 6 has remained the beginning of the tax year ever since, though it was <a href="http://www.timeanddate.com/calendar/julian-gregorian-switch.html">only formalised in 1900</a>. Although some countries, including the US, Canada, France and Germany, have adopted the calendar year as their tax year, the UK and others such as <a href="https://www.ato.gov.au/Individuals/Lodging-your-tax-return/">Australia</a> have not. </p>
<p>Another oddity is the UK government’s own financial year, which runs from April 1 to the following March 31, and so does not coincide with the tax year, although 1 April to 31 March is also the fiscal year for corporation tax. The reason for this is less clear than why April 6 was adopted as the start of the tax year – and is perhaps a tale for another day.</p><img src="https://counter.theconversation.com/content/57247/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jane Frecknall-Hughes does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>It involves shifting calendars, greedy governments – and the Pope.Jane Frecknall-Hughes, Professor of Accounting and Taxation, University of HullLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/540322016-02-25T17:40:03Z2016-02-25T17:40:03ZLeap day: fixing the faults in our stars<figure><img src="https://images.theconversation.com/files/112786/original/image-20160224-16429-bu1c2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An unusual date that comes to us from the heavens.</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-358273034.html">Date image via shutterstock.com</a></span></figcaption></figure><p>The number 2016 divided by 4 equals 504, exactly – with no remainder, which makes the year 2016, like the upcoming years 2020, 2024 and 2028 (and beyond), a leap year. We will get an “extra” day, February 29. </p>
<p>This pattern will repeat until 2100, when the cycle breaks. Though 2100 is exactly divisible by 4, there is an exception – for years whose number is exactly divisible by 100. (On top of that, there’s another exception – for years exactly divisible by 400. So 2400 <em>will</em> be a leap year. Mark your calendars now.)</p>
<p>Where do these quadrennial liberties with our calendar originate? </p>
<p>In the stars, of course.</p>
<h2>Celestial rhythms</h2>
<p>One of the simplest joys of life is to watch the stars, night after night, month after month, year after year. They become old friends. They spend a season, and then move on. Or rather, it is we who move on – ever advancing around the sun toward next week’s deadlines, new constellations, new fashions and new ideas.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/112788/original/image-20160224-16416-1m6rjfu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/112788/original/image-20160224-16416-1m6rjfu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/112788/original/image-20160224-16416-1m6rjfu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/112788/original/image-20160224-16416-1m6rjfu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/112788/original/image-20160224-16416-1m6rjfu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/112788/original/image-20160224-16416-1m6rjfu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/112788/original/image-20160224-16416-1m6rjfu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/112788/original/image-20160224-16416-1m6rjfu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Orion, the annual visitor.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Orion_3008_huge.jpg">Mouser</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>I imagine myself late one night, eight months from now, remembering the overfull recycling bin, at midnight on trash day. As I try to quietly dump wine bottles into the yellow-topped container, there striding over the eastern skyline is <a href="http://www.space.com/16659-constellation-orion.html">Orion</a>. Back again is my ancient friend, telling me that winter is near, and that I have ridden this miraculous rock almost another full lap around my home star. <a href="http://earthsky.org/brightest-stars/blue-white-rigel-is-orions-brightest-star">Rigel</a> shimmers its blue-white light, the twinkle in the eye (the knee, actually) of a companion who has visited me, annually, every place on Earth I have lived since childhood. Even to the Southern Hemisphere, the steady Orion came for a summer visit – cartwheeling upside down, feet over hands.</p>
<p>It is from these celestial cycles that our concepts of time originate, and, ultimately, from which we gain the leap day.</p>
<p>The <em>sidereal year</em> is the length of time it takes for the Earth to return to the same place with respect to the <a href="http://www.william-shakespeare.info/act3-script-text-julius-caesar.htm">“fix’d” and “constant” stars</a>, so that Orion appears exactly in the same place in the sky, at exactly midnight, 365.2563 days later. Stellar friends like that don’t stand you up; they keep their appointments to seven-digit precision (and more).</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/112790/original/image-20160224-18284-klc76h.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/112790/original/image-20160224-18284-klc76h.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/112790/original/image-20160224-18284-klc76h.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=326&fit=crop&dpr=1 600w, https://images.theconversation.com/files/112790/original/image-20160224-18284-klc76h.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=326&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/112790/original/image-20160224-18284-klc76h.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=326&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/112790/original/image-20160224-18284-klc76h.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=410&fit=crop&dpr=1 754w, https://images.theconversation.com/files/112790/original/image-20160224-18284-klc76h.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=410&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/112790/original/image-20160224-18284-klc76h.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=410&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Right over the equator: A diagram showing the sun’s position relative to the Earth at the vernal equinox.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File%3AHeliocentric_rectangular_ecliptic.png">Tfr000</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Our Western calendar is tied to the <em>tropical year</em> – the time between successive <a href="http://solar.physics.montana.edu/ypop/Classroom/Lessons/Sundials/equinox.html">vernal equinoxes</a>. At that moment, the sun’s position in the sky is exactly where the ecliptic (the plane of the solar system and the path that the planets take as they move through the constellations) crosses the celestial equator (the projection of the Earth’s own equator onto the celestial sphere). Straddling the celestial equator, the sun splits its time exactly between the day side and the night side of the Earth. It returns to that place again in roughly 365.24219 days. Roughly.</p>
<p>Now you can see where those alternating “divisible by 4, 100 and 400” leap year rules originate. </p>
<h2>Making up the differences</h2>
<p>At the end of 365 days, there are still 0.24219 days (just shy of six hours) to go before Earth gets back to the equinox line. </p>
<p>After four years, however, this fractional 0.24219 of a day adds up to 0.96876, which is pretty close to one full day. If we were using only a 365-day calendar, the stars, and more importantly the months, corresponding to the seasons – crucial for agricultural societies – would slip behind. This was apparent to the Romans in the first century, as well as to the Olmecs and the <a href="http://www.livescience.com/25662-how-mayan-calendar-works.html">Maya</a> on the other side of the world.</p>
<p>Thus decreed Julius Caesar in 46 B.C.: that every four years an extra day would be added to February. It was called the Julian calendar. But adding one day every four years, in order to make up for that 0.96876 of a day in orbital spare change, is overcompensating. Caesar’s “every four” leap year prescription adds 0.03124 of a day too much. This makes the Julian calendar run fast by just over 600 seconds per year. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/112789/original/image-20160224-18284-8uyemr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/112789/original/image-20160224-18284-8uyemr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/112789/original/image-20160224-18284-8uyemr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=809&fit=crop&dpr=1 600w, https://images.theconversation.com/files/112789/original/image-20160224-18284-8uyemr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=809&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/112789/original/image-20160224-18284-8uyemr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=809&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/112789/original/image-20160224-18284-8uyemr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1016&fit=crop&dpr=1 754w, https://images.theconversation.com/files/112789/original/image-20160224-18284-8uyemr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1016&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/112789/original/image-20160224-18284-8uyemr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1016&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Exception after exception: Christopher Clavius, in a line engraving by E de Boulonois.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Christopher_Clavius._Line_engraving_by_E._de_Boulonois._Wellcome_V0001150.jpg">Wellcome Trust</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Like with the spare coin jar in our house, small change like that takes a while to add up. It wasn’t until the age of Pope Gregory XIII, in 1582, that this mismatch was becoming a problem. After consultation, presumably with God, but particularly with his astronomer, <a href="http://galileo.rice.edu/sci/clavius.html">Christopher Clavius</a>, <a href="http://www.bluewaterarts.com/calendar/NewInterGravissimas.htm">the pope adopted Clavius’ clever solution</a>. </p>
<p>The Julian calendar runs fast by 0.03124 of a day every four years; multiply both sides by 100, and see an excess of about three days after 400 years. Clavius’ solution was to make centuries exceptions – but that would lose too much, <em>four</em> days in 400 years, not three. So Clavius added one back, once every 400 years, starting in 1600.</p>
<p>This Gregorian calendar, which we use today, has the following rules:</p>
<ul>
<li>Every year divisible by 4: add February 29</li>
<li>Every century (1800, 1900, 2000, 2100): do not add February 29</li>
<li>Every century divisible by 400: add February 29</li>
</ul>
<h2>Still finer measurements</h2>
<p>Even with this refinement, there is still orbital change left over. But now we are talking about temporal shavings that are quite small. At this level of precision, <a href="http://tycho.usno.navy.mil/leapsec.html">other wobbles</a> in the relation of the Earth’s rotational period (the day) and its revolution period (the year) have to be <a href="http://thephoenix.com/boston/news/57080-beat-the-clock/">taken into account</a>.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/112791/original/image-20160224-15614-7njtc9.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/112791/original/image-20160224-15614-7njtc9.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/112791/original/image-20160224-15614-7njtc9.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=163&fit=crop&dpr=1 600w, https://images.theconversation.com/files/112791/original/image-20160224-15614-7njtc9.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=163&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/112791/original/image-20160224-15614-7njtc9.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=163&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/112791/original/image-20160224-15614-7njtc9.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=205&fit=crop&dpr=1 754w, https://images.theconversation.com/files/112791/original/image-20160224-15614-7njtc9.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=205&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/112791/original/image-20160224-15614-7njtc9.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=205&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When a leap second is added, digital clocks tick past 23:59:59 but don’t go directly to 00:00:00.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Leap_second.png">Twid</a></span>
</figcaption>
</figure>
<p>Keeping track of minute effects like this is the job of the <a href="http://hpiers.obspm.fr/">International Earth Rotation and Reference Systems Service</a>, which controls the addition (or deletion) of leap seconds. For example, a second was added to <a href="http://www.nhc.noaa.gov/aboututc.shtml">Coordinated Universal Time</a> by the service on <a href="http://www.bbc.com/news/science-environment-33313347">June 30, 2015</a>, due largely to the slowing of the Earth’s rotation by the gravitational pull of the moon. </p>
<p>There are other sources of calendar slip: the <a href="https://www.ngdc.noaa.gov/hazard/11mar2011.html">8.9 magnitude earthquake that triggered the Japanese tsunami on March 11, 2011</a>, for example, shifted the planet’s mass distribution enough to decrease the length of a day by 1.8 microseconds. This will add up to about a second after 1,500 years.</p>
<h2>Using that ‘extra’ time</h2>
<p>Personally, I think we should make February 29, leap day, a global holiday. It should be considered a gift to ourselves, like taking that accumulated spare change to the grocery store coin-counting machine, and trading it for some easier-to-spend bills. It should be a day of celebration, a reward for saving that quarter of a day over the last four years, to be spent on something frivolous. Or it could be a special day to realign our sense of hourly routines, weekly trash pickups, the race to fulfill monthly quotas, to the celestial schedule.</p>
<p>Without that extra day every fourth year, our ancient friends would begin to miss their annual appointments, and start to fall behind in wishing us prompt birthday greetings, like forgetful Facebook friends. Without February 29, roughly, every four years, the “constant stars” would cease to be constant.</p><img src="https://counter.theconversation.com/content/54032/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Hetrick receives funding from the National Science Foundation. </span></em></p>We will get an ‘extra’ day this year, February 29. Where do these quadrennial liberties with our calendar originate?James Hetrick, Professor of Physics and Analytics, University of the PacificLicensed as Creative Commons – attribution, no derivatives.