tag:theconversation.com,2011:/ca/topics/copernicus-18783/articlesCopernicus – The Conversation2024-01-03T20:26:46Ztag:theconversation.com,2011:article/2133582024-01-03T20:26:46Z2024-01-03T20:26:46ZThe strange story of the grave of Copernicus<figure><img src="https://images.theconversation.com/files/565952/original/file-20231215-19-1ympo4.jpg?ixlib=rb-1.1.0&rect=0%2C5%2C3994%2C2862&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Astronomer Copernicus, or Conversations with God (1873)</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Astronomer_Copernicus,_or_Conversations_with_God#/media/File:Jan_Matejko-Astronomer_Copernicus-Conversation_with_God.jpg">Jan Matejko / Wikimedia Commons</a></span></figcaption></figure><p>Nicholas Copernicus was the astronomer who, five centuries ago, explained that Earth revolves around the Sun, rather than vice versa. A true Renaissance man, he also practised as a mathematician, engineer, author, economic theorist and medical doctor.</p>
<p>Upon his death in 1543 in Frombork, Poland, Copernicus was buried in the local cathedral. Over the subsequent centuries, the location of his grave was lost to history.</p>
<h2>Who was Copernicus?</h2>
<figure class="align-right ">
<img alt="A portrait of a serious looking man" src="https://images.theconversation.com/files/565954/original/file-20231215-25-i46ixp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/565954/original/file-20231215-25-i46ixp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=587&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565954/original/file-20231215-25-i46ixp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=587&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565954/original/file-20231215-25-i46ixp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=587&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565954/original/file-20231215-25-i46ixp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=737&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565954/original/file-20231215-25-i46ixp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=737&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565954/original/file-20231215-25-i46ixp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=737&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A portrait of Nicolaus Copernicus from the town hall of Toruń (circa 1580).</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Nicolaus_Copernicus#/media/File:Nikolaus_Kopernikus.jpg">Unknown artist / Wikimedia</a></span>
</figcaption>
</figure>
<p><a href="https://www.nature.com/articles/152408c0">Nicholas Copernicus</a>, or Mikołaj Kopernik in Polish, was born in Toruń in 1473. He was the youngest of four children born to a local merchant. </p>
<p>After his father’s death, Copernicus’s uncle assumed responsibility for his education. The young scholar initially studied at the University of Kraków between 1491 and 1494, and later at Italian universities in Bologna, Padua and Ferrara.</p>
<p>After studying medicine, canon law, mathematical astronomy, and astrology, Copernicus returned home in 1503. He then worked for his influential uncle, Lucas Watzenrode the Younger, who was the Prince-Bishop of Warmia.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/copernicus-revolution-and-galileos-vision-our-changing-view-of-the-universe-in-pictures-60103">Copernicus' revolution and Galileo's vision: our changing view of the universe in pictures</a>
</strong>
</em>
</p>
<hr>
<p>Copernicus <a href="https://pubmed.ncbi.nlm.nih.gov/21614776/">worked as a physician</a> while continuing his research in mathematics. At that time, both astronomy and music were considered branches of mathematics. </p>
<p>During this period, he formulated two influential economic theories. In 1517, he developed the <a href="https://onlinelibrary.wiley.com/doi/10.1111/1468-0289.00063">quantity theory of money</a>, which was later re-articulated by John Locke and David Hume, and popularised by Milton Friedman in the 1960s. In 1519, Copernicus also introduced the concept now known as <a href="https://www.jstor.org/stable/25776118">Gresham’s law</a>, a monetary principle addressing the circulation and valuation of money.</p>
<figure class="align-center ">
<img alt="A photo of a large brick cathedral." src="https://images.theconversation.com/files/548664/original/file-20230917-29-ztk9ck.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548664/original/file-20230917-29-ztk9ck.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548664/original/file-20230917-29-ztk9ck.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548664/original/file-20230917-29-ztk9ck.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548664/original/file-20230917-29-ztk9ck.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548664/original/file-20230917-29-ztk9ck.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548664/original/file-20230917-29-ztk9ck.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">
<figcaption>
<span class="caption">Nicholas Copernicus was buried in Frombork Cathedral.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Archcathedral_Basilica_of_the_Assumption_of_the_Blessed_Virgin_Mary_and_St._Andrew%2C_Frombork#/media/File:Frauenburger_Dom_2010.jpg">Holger Weinant / Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>The Copernican model of the universe</h2>
<p>The cornerstone of Copernicus’s contributions to science was his revolutionary model of the universe. Contrary to the prevailing Ptolemaic model, which maintained that Earth was the stationary centre of the universe, Copernicus argued that Earth and other planets revolve around the Sun.</p>
<p>Copernicus was further able to compare the sizes of the planetary orbits by expressing them in terms of the distance between the Sun and Earth.</p>
<p>Copernicus feared how his work would be received by the church and fellow scholars. His magnum opus, “<a href="https://www.gla.ac.uk/myglasgow/library/files/special/exhibns/month/apr2008.html">De Revolutionibus Orbium Coelestium</a>” (On the Movement of the Celestial Spheres), was only published just before his death in 1543. </p>
<p>The publication of this work set the stage for groundbreaking shifts in our understanding of the universe, paving the way for future astronomers such as Galileo, who was born more than 20 years after Copernicus’s death.</p>
<h2>The search for Copernicus</h2>
<p>The Frombork Cathedral serves as the final resting place of more than 100 people, most of whom lie in unnamed graves.</p>
<p>There were several unsuccessful attempts to locate Copernicus’s remains, dating as far back as the 16th and 17th centuries. Another failed attempt was made by the French emperor Napoleon after the 1807 Battle of Eylau. Napoleon held Copernicus in high regard as a polymath, mathematician and astronomer.</p>
<figure class="align-center ">
<img alt="Photo of the inside of a cathedral" src="https://images.theconversation.com/files/565958/original/file-20231215-17-kqh2zj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565958/original/file-20231215-17-kqh2zj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565958/original/file-20231215-17-kqh2zj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565958/original/file-20231215-17-kqh2zj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565958/original/file-20231215-17-kqh2zj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565958/original/file-20231215-17-kqh2zj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565958/original/file-20231215-17-kqh2zj.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">
<figcaption>
<span class="caption">Historians believed Copernicus would have been buried near a particular altar in Frombork Cathedral.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Archcathedral_Basilica_of_the_Assumption_of_the_Blessed_Virgin_Mary_and_St._Andrew%2C_Frombork#/media/File:Frombork_Cathedral_Interior.jpg">Julian Nyča / Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>In 2005, a group of Polish archaeologists took up the search. </p>
<p>They were guided by the theory of historian Jerzy Sikorski, who claimed that Copernicus, serving as the Canon of Frombork Cathedral, would have been buried near the cathedral altar for which he was responsible during his tenure. This was the Altar of Saint Wacław, now known as the Altar of the Holy Cross.</p>
<p>Thirteen skeletons were discovered near this altar, including an <a href="https://www.smithsonianmag.com/history/copernicus-unearthed-115715830/">incomplete skeleton</a> belonging to a male aged between 60 and 70 years. This particular skeleton was identified as the closest match to that of Copernicus. </p>
<h2>Forensic science</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/548662/original/file-20230917-23-c6vx5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Photos of a human skull from the front and side." src="https://images.theconversation.com/files/548662/original/file-20230917-23-c6vx5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/548662/original/file-20230917-23-c6vx5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548662/original/file-20230917-23-c6vx5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548662/original/file-20230917-23-c6vx5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548662/original/file-20230917-23-c6vx5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548662/original/file-20230917-23-c6vx5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548662/original/file-20230917-23-c6vx5.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">A skull believed to belong to Copernicus.</span>
<span class="attribution"><a class="source" href="https://clkp.policja.pl/clk/badania-i-projekty/ciekawe-badania/172502,Czy-tak-wygladal-Mikolaj-Kopernik.html">Dariusz Zajdel / Centralne Laboratorium Kryminalistyczne Policji</a></span>
</figcaption>
</figure>
<p>The skull of the skeleton served as the basis for a facial reconstruction.</p>
<p>In addition to morphological studies, DNA analysis is often used for the <a href="https://www.pnas.org/doi/10.1073/pnas.0907491106">identification of historical or ancient remains</a>. In the case of the presumed remains of Copernicus, a genetic identification was possible due to the well-preserved state of the teeth. </p>
<p>A significant challenge lay in identifying a suitable source of reference material. There were no known remains of any relatives of Copernicus.</p>
<h2>An unlikely find</h2>
<p>In 2006, however, a new source of DNA reference material came to life. An astronomical reference book used by Copernicus for many years was found to contain hair among its pages. </p>
<p>This book had been taken to Sweden as war booty following the Swedish invasion of Poland in the mid-17th century. It is currently in the possession of the Museum Gustavianum at Uppsala University. </p>
<p>A meticulous examination of the book revealed several hairs, thought likely to belong to the book’s primary user, Copernicus himself. Consequently, these hairs were assessed as potential reference material for genetic comparison with the teeth and bone matter recovered from the tomb.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/who-owned-this-stone-age-jewellery-new-forensic-tools-offer-an-unprecedented-answer-204797">Who owned this Stone Age jewellery? New forensic tools offer an unprecedented answer</a>
</strong>
</em>
</p>
<hr>
<p>The hairs were compared with the <a href="https://cs.astronomy.com/asy/b/astronomy/archive/2009/10/22/nicolaus-copernicus-old-old-blue-eyes.aspx">DNA from the teeth and bones</a> of the discovered skeleton. Both the mitochondrial DNA from the teeth and the skeletal sample matched those of the hairs, strongly suggesting that the remains were indeed those of Nicholas Copernicus.</p>
<p>The multidisciplinary effort, involving archaeological excavation, morphological studies and advanced DNA analysis, has led to a compelling conclusion. </p>
<p>The remains discovered near the Altar of the Holy Cross in Frombork Cathedral are highly likely to be those of Nicholas Copernicus. This monumental find not only sheds light on the final resting place of one of the most influential figures in the history of science, but also showcases the depth and sophistication of modern scientific methods in corroborating historical data.</p><img src="https://counter.theconversation.com/content/213358/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Darius von Guttner Sporzynski 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>A team of archaeologists discovered the remains of the 16th-century father of modern astronomy, who demonstrated that the Earth orbits the Sun.Darius von Guttner Sporzynski, Historian, Australian Catholic UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1527772021-01-12T15:07:36Z2021-01-12T15:07:36ZSouth African astronomy has a long, rich history of discovery – and a promising future<figure><img src="https://images.theconversation.com/files/377956/original/file-20210111-23-12bfk2d.jpg?ixlib=rb-1.1.0&rect=4%2C492%2C2748%2C1655&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Southern African Large Telescope has been a key part of South Africa's astronomical contributions.</span> <span class="attribution"><span class="source">SAAO</span></span></figcaption></figure><p>The <a href="https://www.saao.ac.za/">South African Astronomical Observatory</a> in Cape Town is the oldest permanent observatory in the southern hemisphere: it turned 200 in 2020. </p>
<p>This observatory is a fundamental part of South Africa’s long history of astronomical research, which began when French academic <a href="https://academic.oup.com/astrogeo/article/43/2/2.25/281196">Nicolas-Louis de La Caille</a> visited Cape Town from 1751 to 1753. He undertook a careful examination of every square degree of the southern sky. This resulted in the first comprehensive sky survey ever made, in either hemisphere.</p>
<p>The Royal Observatory, Cape Town of Good Hope (today the South African Astronomical Observatory) was established in 1820. It became – and remained for 150 years – the most important source of star positions in the southern hemisphere sky. This was in terms of both accuracy and the number of measurements made. In the years that followed its foundation, the observatory’s laborious work led to important scientific discoveries. </p>
<p>Cape astronomers were responsible for, among other things, the first measurement of the distance to a star; the first photographic sky survey and the accurate measurement of the distance to the sun. They were at the forefront of developments in stellar spectroscopy. This is the detailed analysis of a star’s light to find out its composition and movement towards or away from the sun. They also determined the shape of the earth in the southern hemisphere and conducted the first accurate country-wide survey measurements of southern Africa. </p>
<h2>Measuring stellar distances</h2>
<p>In 1543 the mathematician and astronomer <a href="https://plato.stanford.edu/entries/copernicus/">Nicolaus Copernicus</a> asserted that the earth orbits the sun. This meant that people should be able to observe the apparent shift in the position of the nearest stars from different points in the earth’s orbit. But that had not been observed in the centuries that followed. The reason was, of course, that even the nearest stars are incredibly far away and the effect being looked for is very small. </p>
<p>When the Royal Observatory was founded in 1820, it was equipped with the most accurate star position measuring devices available. Eleven years later Thomas Henderson used those devices to make the first believable measurements of this effect, known as “<a href="https://www.space.com/30417-parallax.html">parallax</a>”. By observing the angular “movement” of Alpha Centauri – still the second-closest star known to us – and knowing also the size of the earth’s orbit, this gave the distance to the star by simple trigonometry. </p>
<p>A different technology, photography, would lead to more important astronomical discoveries at the Cape. All observatories in the 19th century made precise observations of star positions one by one and published catalogues of these. In 1882 the head of the Royal Observatory, David Gill, was surprised to receive a letter from a Mr Simpson, an amateur photographer in Aberdeen, a town elsewhere in the Cape. </p>
<p>Simpson had managed to photograph a bright comet that had just appeared. His photographic plates were sensitive enough to register stars in the background. This led to a “lightbulb” moment for Gill: he realised that the positions of stars could now be recorded in quantity on a permanent medium, more reliably than any visual observer could ever hope to do. </p>
<p>So he set up a special photographic telescope using the largest lens that he could find and set about making the first photographic star catalogue. This was called the <a href="http://adsabs.harvard.edu/full/1896AnCap...3....1G">Cape Photographic Durchmusterung</a> after its much more laboriously compiled northern hemisphere equivalent, put together in Bonn, Germany. </p>
<p>But it wasn’t just Cape Town that hosted an important astronomical site.</p>
<p>In 1903, the <a href="https://www.saasta.ac.za/johannesburg-observatory/">Johannesburg Observatory</a> was established. It achieved its greatest success in 1915 when its director, Robert Innes, discovered a very faint star near Alpha Centauri. </p>
<p>On various grounds he claimed it to be the nearest star to Earth; it took many years of investigation before this could be verified. The new discovery was named “Proxima Centauri”, meaning the nearest in the constellation Centaurus. Not only was it the nearest star but at that time of discovery it was the least luminous star ever discovered. Other dimmer stars have been found since, but Proxima still retains its nearest star status and its distance has been thoroughly verified from space satellites. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/seti-new-signal-excites-alien-hunters-heres-how-we-could-find-out-if-its-real-152498">SETI: new signal excites alien hunters – here's how we could find out if it's real</a>
</strong>
</em>
</p>
<hr>
<h2>Doubling the size of the Universe</h2>
<p>In 1948 the private Radcliffe Foundation in the United Kingdom set up in Pretoria what was for a time the largest telescope in the southern hemisphere and joint fourth largest in the world. This is a title currently held by the <a href="https://www.salt.ac.za/">Southern African Large Telescope</a>. </p>
<p>Early on in the Radcliffe’s existence the then director, David Thackeray, and his colleague Adriaan Wesselink discovered in our neighbouring galaxy, the Large Magellanic Cloud, a number of RR Lyrae variable stars that astronomers using smaller telescopes could not detect. These are stars that change their brightness in a well-defined manner over a cycle of a few days and whose average “wattage” is completely predictable.</p>
<p>By measuring the Magellanic Cloud stars’ average apparent brightnesses and comparing them to other RR Lyrae stars at known distances they determined that the cosmic distance scale originally published two decades before by Edwin Hubble and others was underestimated by about a factor of two. In effect, they doubled the size of the Universe. This result was announced to great acclaim at the triennial meeting of the <a href="http://adsabs.harvard.edu/full/1952JRASC..46..217D">International Astronomical Union in 1952</a>. </p>
<h2>More to come</h2>
<p>Today South African astronomy remains at the forefront of many initiatives and discoveries. It has become a leader in the field of radio astronomy with the MeerKAT telescope near Carnarvon and will within a decade be the host of an international project, the <a href="https://www.skatelescope.org/">Square Kilometre Array</a>.</p>
<p><em>This article is adapted from <a href="https://www.nrf.ac.za/sites/default/files/documents/04%20NRF%20SMM%20V3%20Issue3%20Highlights%20of%20Astronomy%20in%20South%20Africa%20Before%201972.pdf">a piece</a> that initially appeared in the South African National Research Foundation’s Science Matters Magazine.</em></p><img src="https://counter.theconversation.com/content/152777/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Glass 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>Cape astronomers were responsible for, among other things, the first measurement of the distance to a star; the first photographic sky survey and the accurate measurement of the distance to the sun.Ian Glass, Associate Research Astronomer, South African Astronomical ObservatoryLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1523702020-12-21T17:13:00Z2020-12-21T17:13:00ZThe ‘Christmas Star’ appears again: Jupiter and Saturn align in the ‘great conjunction’ on Dec. 21, 2020<figure><img src="https://images.theconversation.com/files/376184/original/file-20201221-15-1sejjhd.jpg?ixlib=rb-1.1.0&rect=40%2C62%2C2690%2C1931&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">On Dec. 21, Jupiter and Saturn will be so close together they will almost appear to be touching.</span> <span class="attribution"><span class="source">(Unsplash)</span></span></figcaption></figure><p>Jupiter and Saturn lined up on Dec. 21, so close together that they appeared as one bright shining star. Many referred to it as the “Christmas Star.” It’s the <a href="https://www.scientificamerican.com/article/jupiter-and-saturns-great-conjunction-is-the-best-in-800-years-heres-how-to-see-it/">closest the two planets have appeared together in about 800 years</a>, and won’t occur again until 2080.</p>
<p>This conjunction of Jupiter and Saturn may have an even closer tie to the Biblical story of the birth of Jesus Christ than its occurrence so close to Christmas this year. As noted by Johannes Kepler in the 17th century, a similar conjunction occurred in 7 BCE and could be the astronomical origin of the Star of Bethlehem that guided the wise men.</p>
<p>But there are notable differences between the two events, and the full story has several interesting ties to the history of astronomy, starting with the origins of the word “planet,” which <a href="https://www.etymonline.com/word/planet">comes from the Greek word meaning “wanderer.”</a></p>
<p>The planets have always been recognizable to astronomers, not only because they are relatively bright points of light among the stars, but because of their unique wandering nature. This posed a problem to ancient astronomers, which lasted more than 2,000 years and was only resolved during the Scientific Revolution.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sunset view of planets" src="https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=511&fit=crop&dpr=1 754w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=511&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/376231/original/file-20201221-15-dgnu5g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=511&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 graphic made from a simulation program, showing a view of the 2020 great conjunction through the naked eye just after sunset at approximately 5:15 p.m. (EST) on Dec. 21.</span>
<span class="attribution"><span class="source">(NASA)</span></span>
</figcaption>
</figure>
<h2>The motion of the planets</h2>
<p>As the Earth spins on its axis every 24 hours, the sun, moon, stars and planets all appear to move across our sky, rising in the East and setting in the West. But because the planets orbit the sun, all travelling in counterclockwise directions when viewed from above the North Pole, to us on Earth the sun and planets all appear to move with respect to the background stars. </p>
<p>As Earth moves around the sun, the sun in turn appears to move slowly to the East, by about a degree each day as it travels through the <a href="https://earthsky.org/space/what-is-the-ecliptic">Zodiac constellations</a>. Mercury and Venus move from one side of the sun to the other as they circle it. And the outer planets of the solar system — Mars, Jupiter and Saturn are visible to the naked eye — appear to move East through the stars as they orbit the sun.</p>
<p>But a peculiar thing happens to the positions of the outer planets when the Earth passes between them and the sun: They appear to briefly reverse direction, and travel West, against the background stars. This <a href="https://earthsky.org/space/what-is-retrograde-motion">apparent retrograde motion</a> is caused by a parallax shift that occurs for the same reason your thumb hops back and forth if you hold it fixed in front of your face and wink first with one eye, then the other; it’s an optical illusion caused by a shift in our perspective.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=623&fit=crop&dpr=1 600w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=623&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=623&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=783&fit=crop&dpr=1 754w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=783&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/376170/original/file-20201221-17-ww488o.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=783&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 Earth-centred model of planetary motions could explain why other planets sometimes appeared to be moving backwards. Nicolaus Copernicus proposed a sun-centred theory in 1543.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Ptolemaic_system.png">(Muhammad/Wikimedia)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>While the Ancient Greeks had considered this explanation of the retrograde motions of planets, they mainly preferred an alternate, <a href="http://galileo.rice.edu/sci/theories/ptolemaic_system.html">Earth-centred model</a> in which the planets move around a fixed Earth on small circular orbits, the centres of which went around larger, Earth-centred circles. Thus, as the planets orbited an empty point in space while that point went around the Earth, the planets would occasionally stop and move backwards in their motion against the background stars. </p>
<p>Astronomers mainly described the solar system in this Earth-centred way until Nicolaus Copernicus proposed a <a href="https://earthobservatory.nasa.gov/features/OrbitsHistory">sun-centred theory in 1543</a>. Copernicus’s theory didn’t do any better job of describing planetary motion than the Earth-centred models did, but the idea gained traction.</p>
<p>The German 17th-century astronomer Johannes Kepler eventually found the key to describing planetary motion in a sun-centred system. Rather than orbiting the sun in circles, Kepler found the <a href="https://solarsystem.nasa.gov/resources/310/orbits-and-keplers-laws/">planets moved in ellipses</a>, a distinction that allowed him to precisely predict their observed positions. </p>
<h2>Christmas Star</h2>
<p>A conjunction is said to happen when two astronomical objects pass each other due to their movement along the direction of the stars’ daily rotation. Since solar system objects do not all move within precisely the same plane, conjunctions can sometimes happen with a wide separation. Since Jupiter orbits the sun every 11.9 years while Saturn’s orbit takes 29.5 years, it happens that a conjunction of Jupiter and Saturn — called a “great conjunction” due to its rarity — occurs roughly every 20 years.</p>
<figure class="align-center ">
<img alt="Night sky with two bright planets." src="https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/376190/original/file-20201221-23-1y3eslv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Conjunction of Jupiter (top) and Venus (bottom) in 2015.</span>
<span class="attribution"><span class="source">(Mike Pennington)</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Most great conjunctions are not particularly notable. But occasionally, like this year, Jupiter and Saturn cross paths so close to each other that they can be barely distinguishable to the naked eye. Or sometimes the two planets cross paths when they are opposite the sun, so their apparent retrograde motion results in a triple conjunction, as was the case in 7 BCE.</p>
<p>In 1604, while he was working in Prague, <a href="https://www.nature.com/articles/462987a">Kepler observed the tight arrangement of three planets — Mars, Saturn and Jupiter — and a bright new star, a supernova, that would slowly fade over the course of a year</a>. This occurrence inspired him to consider a similar set of events that might have led the wise men to Bethlehem in time for Jesus Christ’s birth. </p>
<p>Knowing that Herod the Great had died in 4 BCE, he placed the birth of Christ before that date. And using his knowledge of planetary motion, he found that Jupiter and Saturn underwent a triple conjunction in 7 BCE, that conjunctions of Mars with each planet in 6 BCE were shortly followed by conjunctions of the planets with the sun. Kepler <a href="http://articles.adsabs.harvard.edu//full/1937JRASC..31..417B/0000421.000.html">suggested that these solar conjunctions aligned with the conception of Christ and that the wise men arrived the following year to witness Christ’s birth beneath the Star of Bethlehem</a>.</p>
<h2>Significance of the great conjunction</h2>
<p>On Dec. 21 of this year, Jupiter and Saturn were only one-tenth of a degree apart, well within the field of any telescope’s view. With this year’s event, it is worth keeping in mind the historical significance previous conjunctions have had. </p>
<p>Kepler’s fascination with planetary motion led, only a handful of years later, to his discovery that planets follow elliptical paths around the sun. And Kepler’s discovery would, before the end of that century, <a href="https://www.pbs.org/wgbh/nova/newton/principia.html">inspire Newton’s work on his most important contribution</a>, the great <em>Philosophiae Naturalis Principia Mathematica</em>, where he laid down his ideas on the law of gravity, and which forever changed the world of science. </p>
<p>Without fear of exaggeration, it’s possible to link the wandering motion of the planets — never more clearly on display than when we can simultaneously see Saturn’s rings and the Galilean moons of Jupiter through a telescope — with the discovery that Earth is a planet within a solar system in which motions are dominated by a universal gravitation that acts between all massive bodies.</p>
<p><em>This is a corrected version of a story originally published on Dec. 21. The earlier story said a conjunction aligned with Immaculate Conception instead of the conception of Christ.</em></p><img src="https://counter.theconversation.com/content/152370/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daryl Janzen 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>From the birth of Jesus Christ to Newton’s discovery of gravity, great conjunctions of Jupiter and Saturn have many notable connections in human history.Daryl Janzen, Observatory Manager and Instructor, Astronomy, University of SaskatchewanLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1288182020-01-24T13:39:36Z2020-01-24T13:39:36ZWhy your zodiac sign is probably wrong<figure><img src="https://images.theconversation.com/files/309355/original/file-20200109-80169-1wreuwe.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1991%2C1476&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">As the Earth orbits the Sun, the Sun appears to move through the ancient constellations of the zodiac.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Ecliptic_path.jpg">Tauʻolunga/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>I was born a Capricorn (please don’t judge me), but the Sun was in the middle of Sagittarius when I was born. </p>
<p>As a <a href="http://stars.astro.illinois.edu/">professor emeritus of astronomy</a>, I am often asked about the difference between astrology and astronomy. The practice of astrology, which predicts one’s fate and fortune based on the positions of the Sun, Moon, stars and planets, dates back to ancient times. It was intermingled with the science of astronomy back then – in fact, many astronomers of old made scientific observations that are valuable even today. But once Copernicus, Kepler and Galileo realized the planets orbit the Sun, rather than the Earth, and Newton discovered the physical laws behind their behavior, astrology and astronomy split, never to be reunited. </p>
<p>The science of astronomy is now at odds with one of the basic organizing principles in astrology – the dates of the zodiac.</p>
<h2>The constellations of the zodiac</h2>
<p>Over the course of a year, the Sun appears to pass through a belt of sky containing 12 ancient constellations, or groupings, of stars. They are collectively called the zodiac and consist almost entirely of animal figures, like the ram (Aries), crab (Cancer) and lion (Leo). It is a disappointment to many that the constellations only rarely look like what they represent. How could they, since they are truly random scatterings of stars? They are meant to represent, not to portray.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/309733/original/file-20200113-103974-7f1x7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309733/original/file-20200113-103974-7f1x7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=509&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309733/original/file-20200113-103974-7f1x7p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=509&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309733/original/file-20200113-103974-7f1x7p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=509&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309733/original/file-20200113-103974-7f1x7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=640&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309733/original/file-20200113-103974-7f1x7p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=640&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309733/original/file-20200113-103974-7f1x7p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=640&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The word ‘zodiac’ comes from a Greek phrase that means ‘circle of animals’.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/zodiac-constellations-zodiacal-calendar-dates-astrological-1562183209">Tartila/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>Although the constellations of the zodiac, which date back to Mesopotamia or before, may seem definitive, they are only one example of those produced by the various cultures of the world, all of which had their own, frequently very different, notions of how the sky is constructed. The Incas, for example, made constellations not from stars, but from the <a href="https://www.thoughtco.com/inca-star-worship-and-constellations-2136315">dark patches in the Milky Way</a>. </p>
<p>The number of constellations in the Western zodiac comes from the cycles of the Moon, which orbits the Earth 12.4 times a year. Roughly speaking, the Sun appears against a different constellation every new Moon, the stars forming a distant backdrop to the Sun. Though the stars are not visible during daytime, you can know what constellation the Sun is in by looking at the nighttime sky. There you will see the opposite constellation.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/310567/original/file-20200116-181617-c3nx4x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/310567/original/file-20200116-181617-c3nx4x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/310567/original/file-20200116-181617-c3nx4x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=346&fit=crop&dpr=1 600w, https://images.theconversation.com/files/310567/original/file-20200116-181617-c3nx4x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=346&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/310567/original/file-20200116-181617-c3nx4x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=346&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/310567/original/file-20200116-181617-c3nx4x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=435&fit=crop&dpr=1 754w, https://images.theconversation.com/files/310567/original/file-20200116-181617-c3nx4x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=435&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/310567/original/file-20200116-181617-c3nx4x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=435&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 Sun is in Leo here, which means at night, you’d see Aquarius.</span>
<span class="attribution"><a class="source" href="https://www.pngguru.com/free-transparent-background-png-clipart-gmeeu">PNGGuru</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Astrology suggests that each sign of the zodiac fits neatly into a 30-degree slice of sky – which multiplied by 12 adds up to 360 degrees. In actuality, this is not the case, as the constellations vary a great deal in shape and size. For example, the Sun passes through the constellation Scorpio in just five days, but takes 38 days to pass through Taurus. This is one of the reasons astrological signs do not line up with the constellations of the zodiac.</p>
<h2>Precession of the equinoxes</h2>
<p>The main reason astrological signs fail to line up with the zodiac, though, is a wobble in the Earth’s rotational axis called <a href="https://www.britannica.com/science/precession">precession</a>. As a result of its rotation, the Earth bulges slightly at the equator, not unlike how a skater’s skirt fans out as she spins. The gravity of the Moon and Sun pull on the bulge, which causes the Earth to wobble like a top. The wobble causes the Earth’s axis, which is the center line around which it rotates, to swing in a slow circle over the course of 25,800 years.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/qlVgEoZDjok?wmode=transparent&start=39" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A wobbling Earth causes the dates of the zodiac to shift from those established in ancient times.</span></figcaption>
</figure>
<p>This movement alters the view of the zodiac from Earth, making the constellations appear to slide to the east, roughly a degree per human lifetime. Though slow, precession was discovered with the naked eye by <a href="http://abyss.uoregon.edu/%7Ejs/glossary/hipparchus.html">Hipparchus of Nicaea</a> around 150 B.C.</p>
<p>In ancient times, the vernal equinox – or the first day of spring – was in Aries. Due to precession, it moved into Pisces <a href="http://stars.astro.illinois.edu/books.html#sky">around 100 B.C., where it is now and will remain until A.D. 2700</a>, when it will move into Aquarius and so on. Over the course of 25,800 years, it will eventually return to Aries and the cycle will begin again.</p>
<p><iframe id="x0CHI" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/x0CHI/3/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>As a game, astrology and its predictions of fate and personality can be fun. However the subject has no basis in science. It is to science what the game “Monopoly” is to the real estate market. </p>
<p>Astrology diverts attention away from the very real influences of the planets, primarily their gravitational effects on one another that cause real changes in the shapes, sizes and tilts of their orbits. On Earth, <a href="https://doi.org/10.1038/nature07867">such changes likely caused past ice ages</a>. Direct collisions between Earth and celestial bodies can cause very rapid changes, such as the impact of an asteroid off the Yucatan Peninsula <a href="https://www.smithsonianmag.com/science-nature/dinosaur-killing-asteroid-impact-chicxulub-crater-timeline-destruction-180973075/">66 million years ago that had global effects</a> including the disappearance of dinosaurs and the rise of mammals.</p>
<p>Astronomical studies will eventually allow the prediction of such events, while astrological predictions will get you absolutely nowhere.</p>
<hr>
<p><em>This story has been updated to correct the animal that Aries represents. The chart has been updated to include Oct. 31 under Virgo, where it falls most years.</em></p><img src="https://counter.theconversation.com/content/128818/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James B. Kaler 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>Astronomy and astrology do not agree on the dates of the zodiac constellations.James B. Kaler, Professor Emeritus of Astronomy, University of Illinois at Urbana-ChampaignLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/803092017-08-09T00:28:51Z2017-08-09T00:28:51ZEclipsing the occult in early America: Benjamin Franklin and his almanacs<figure><img src="https://images.theconversation.com/files/181273/original/file-20170807-2667-6m8q7c.jpg?ixlib=rb-1.1.0&rect=29%2C801%2C6501%2C5729&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Franklin's lifelong quest was spreading scientific knowledge to regular people.</span> <span class="attribution"><a class="source" href="http://www.loc.gov/pictures/item/2003674083/">Mason Chamberlin</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>By the time he was 20 years old, colonial American Benjamin Franklin had already spent two years working as a printer in London. He returned to Philadelphia in 1726. During the sea voyage home, he kept a journal that included many of his observations of the natural world. Franklin was inquisitive, articulate and <a href="http://www.pbs.org/benfranklin/l3_inquiring_weather.html">interested in mastering the universe</a>.</p>
<p>During one afternoon calm on September 14, Franklin wrote,</p>
<blockquote>
<p>“as we sat playing Draughts upon deck, we were surprised with a sudden and unusual darkness of the sun, which as we could perceive was only covered with a small thin cloud: when that was passed by, we discovered that that glorious luminary laboured under a very great eclipse. At least ten parts out of twelve of him were hid from our eyes, and we were apprehensive he would have been totally darkened.”</p>
</blockquote>
<p>Total solar eclipses are not rare phenomena; <a href="https://www.space.com/25644-total-solar-eclipses-frequency-explained.html">every 18 months</a> on average one occurs somewhere on Earth. Franklin and his shipmates likely had seen eclipses before. What was different for Franklin and his generation was a new understanding of the causes of eclipses and the possibility of accurately predicting them.</p>
<p>Earlier generations in Europe relied on magical thinking, interpreting such celestial events through the lens of the occult, as if the universe were sending a message from heaven. By contrast, Franklin came of age at a time when supernatural readings were held in suspicion. He would go on to spread modern scientific views of astronomical events through his popular almanac – and attempt to free people from the realm of the occult and astrological prophecy.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=501&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=501&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=501&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=629&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=629&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=629&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ptolemy’s Earth-centered universe with the moon, Mercury, Venus, the sun, Mars, Jupiter and Saturn orbiting our planet.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Planisphaerium_Ptolemaicum_siue_machina_orbium_mundi_ex_hypothesi_Ptolemaica_in_plano_disposita_(2709983277).jpg">Andreas Cellarius</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Beyond divine heavens with modern astronomy</h2>
<p>Ancient people conceived of the heavens as built around human beings. For centuries, people subscribed to the <a href="http://galileo.rice.edu/sci/theories/ptolemaic_system.html">Ptolemaic belief about the solar system</a>: The planets and the sun revolved around the stationary Earth.</p>
<p>The idea that God drove the heavens is very old. Because people thought that their god (or gods) guided all heavenly occurrences, it’s not surprising that many people – <a href="http://idp.bl.uk/4DCGI/education/astronomy/sky.html">ancient Chinese</a>, for example, and <a href="http://www.ibtimes.co.uk/solar-eclipse-apocalypse-how-ancient-civilisations-explained-disappearance-sun-1492508">Egyptians and Europeans</a> – believed that what they witnessed in the skies above provided signs of future events. </p>
<p>For this reason, solar eclipses were for many centuries understood to be harbingers of good or evil for humankind. They were attributed <a href="https://www.timeanddate.com/eclipse/solar-eclipse-history.html">magical or mysterious predictive qualities</a> that could influence human lives. During the first century A.D., people – including astrologers, magicians, alchemists and mystics – who claimed to have mastery over supernatural phenomena held sway over kings, religious leaders and whole populations.</p>
<p>Nicholas Copernicus, whose life straddled the 15th and 16th centuries, used scientific methods to devise a more accurate understanding of the solar system. In his famous book, “On the Revolutions of the Celestial Spheres” (published in 1543), Copernicus showed that the planets revolved around the sun. He didn’t get it all right, though: He thought planetary bodies had circular orbits, because the Christian God would have designed perfect circles in the cosmos. That planetary motion is elliptical is a later discovery.</p>
<p>By the time Benjamin Franklin grew up in New England (about 150 years later), few people still believed in the Ptolemaic system. Most had learned from living in an increasingly enlightened culture that the Copernican system was more reliable. Franklin, like many in his generation, believed that knowledge about the scientific causes for changes in the environment could work to reduce human fears about what the skies might portend. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=861&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=861&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=861&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1081&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1081&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1081&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">By measuring the height of celestial objects with an astrolabe, a user could predict the position of stars, planets and the sun.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Astrolabe_planisférique.jpg">Pom²</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>It was an age of wonder, still, but wonder was harnessed to technological advances that could help people understand better the world they lived in. Accurate instruments, such as the astrolabe, allowed people to measure the motion of the planets and thus predict movements in the heavens, particularly phenomena like solar and lunar eclipses and the motions of planets like Venus.</p>
<p>In his earliest printed articles, Franklin criticized the idea that education belonged solely to the elite. He hoped to bring knowledge to common people, so they could rely on expertise outside of what they might hear in churches. Franklin opted to use his own almanacs – along with his satirical pen – to help readers distinguish between astronomical events and astrological predictions.</p>
<h2>Old-fashioned almanacs</h2>
<p>Printing was a major technological innovation during the 16th, 17th and 18th centuries that helped foster information-sharing, <a href="https://sites.google.com/a/umich.edu/from-tablet-to-tablet/final-projects/-almanacs-in-17th-and-18th-century-america-michael-myckowiak-14">particularly via almanacs</a>.</p>
<p>These amazing compilations included all kinds of useful information and were relied on by farmers, merchants, traders and general readers in much the same way we rely on smartphones today. Colonial American almanacs provided the estimated times of sunrises and sunsets, high and low tides, periods of the moon and sun, the rise and fall of constellations, solar and lunar eclipses, and the transit of planets in the night skies. More expensive almanacs included local information such as court dates, dates of markets and fairs, and roadway distances between places. Most almanacs also offered standard reference information, including lists of the reigns of monarchs of England and Europe, along with a chronology of important dates in the Christian Era. </p>
<p><a href="https://newenglandquarterly.wordpress.com/2013/08/27/colonial-almanacs/">Almanac culture dominated New England life</a> when Franklin was a youth. They were the most purchased items American printers offered, with many a printer making his chief livelihood by printing almanacs.</p>
<p>Almanacs were money-makers, so <a href="http://www.librarycompany.org/BFWriter/poor.htm">Franklin developed his own version</a> shortly after he opened his own shop in Philadelphia. The city already had almanac-makers – Titan Leeds and John Jerman, among others – but Franklin aimed to gain the major share of the almanac trade.</p>
<p>Franklin considered astrological prediction foolish, especially in light of new scientific discoveries being made about the universe. He thought almanacs should not prognosticate on future events, as if people were still living in the dark ages. So he found a way to <a href="http://www.vlib.us/amdocs/texts/prichard44.html">make fun of his competitors</a> who continued to pretend they could legitimately use eclipses, for instance, to predict future events.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=590&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=590&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=590&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Franklin dispensed many aphorisms in the guise of ‘Poor Richard,’ such as ‘Love your Enemies, for they tell you your Faults.’</span>
<span class="attribution"><a class="source" href="http://www.loc.gov/pictures/item/2003654338/">Oliver Pelton</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Introducing Poor Richard</h2>
<p>In addition to the usual fare, <a href="http://www.benjamin-franklin-history.org/poor-richards-almanac/">Franklin’s almanac provided</a> stories, aphorisms and poems, all ostensibly curated by a homespun character he created: <a href="http://www.librarycompany.org/BFWriter/poor.htm">Richard Saunders, the fictional “author”</a> of Franklin’s “Poor Richard’s Almanac.”</p>
<p>The “Poor Richard” Saunders persona allowed Franklin to satirize almanac makers who still wrote about eclipses as occult phenomena. Satire works because it closely reproduces the object being made fun of, with a slight difference. We’re familiar with this method today from watching skits on “Saturday Night Live” and other parody programs.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1094&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1094&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1094&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1375&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1375&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1375&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Title page of Franklin’s first ‘Poor Richard’ almanac, for 1733.</span>
</figcaption>
</figure>
<p>Franklin’s voice was close enough to his satirical target that “Poor Richard” stole the market. For instance, Poor Richard began his career by predicting the death of Titan Leeds, his competitor. He later would do the same thing to John Jerman. Franklin was determined to mock almanac-makers who pretended to possess occult knowledge. Nobody knows when a person might die, and only astrologers would pretend to think a solar or lunar eclipse might mean something for humans.</p>
<p>Franklin included a wonderfully funny section in his almanac for 1735, making light of his competitors who did offer astrological prognostications. As “Poor Richard,” he wrote:</p>
<blockquote>
<p>“I shall not say much of the Signification of the Eclipses this Year, for in truth they do not signifie much; only I may observe by the way, that the first Eclipse of the Moon being celebrated in Libra or the Ballance, foreshews a Failure of Justice, where People judge in their own Cases. But in the following Year 1736, there will be six Eclipses, four of the Sun, and two of the Moon, which two Eclipses of the Moon will be both total, and portend great Revolutions in Europe, particularly in Germany….”</p>
</blockquote>
<p>Richard Saunders is clear in the opening remark that “Eclipses … do not signifie much.” He nonetheless goes on to base amazing predictions for 1736 on them, in effect lampooning anyone who would rely on the stars to foretell human events. Great revolutions were taking place in Europe, but no one needed to read eclipses in order to figure that out; they needed only to read the day’s newspapers.</p>
<p>The next year, Franklin decided go a step further than just satirizing these occult prognostications. He had Richard Saunders explain his understanding of some of the science behind eclipses. He characterized the “Difference between Eclipses of the Moon and of the Sun” by reporting that:</p>
<blockquote>
<p>“All Lunar Eclipses are universal, i.e. visible in all Parts of the Globe which have the Moon above their Horizon, and are every where of the same Magnitude: But Eclipses of the Sun do not appear the same in all Parts of the Earth where they are seen; being when total in some Places, only partial in others; and in other Places not seen at all, tho’ neither Clouds nor Horizon prevent the Sight of the Sun it self.”</p>
</blockquote>
<p>The goal of an explanation like this? To eclipse occult belief. He hoped people would become more confident about the universe and everything in it and would learn to rely on <a href="http://nationaleclipse.com/history.html">scientifically validated knowledge</a> rather than an almanac-maker’s fictions.</p><img src="https://counter.theconversation.com/content/80309/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Carla J. Mulford 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>Franklin advanced a scientific – not supernatural – understanding of astronomical events such as eclipses. His satirical character ‘Poor Richard’ mocked those who bought into astrological predictions.Carla J. Mulford, Professor of English, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/601032016-05-30T20:20:29Z2016-05-30T20:20:29ZCopernicus’ revolution and Galileo’s vision: our changing view of the universe in pictures<figure><img src="https://images.theconversation.com/files/124244/original/image-20160527-22063-xrogic.png?ixlib=rb-1.1.0&rect=0%2C991%2C2200%2C2025&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Galileo's sketches of the moon, showing its phases.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Galileo%27s_sketches_of_the_moon.png">Wikimedia/Galileo</a></span></figcaption></figure><p>It’s not a stretch to say the Copernican revolution fundamentally changed the way we think about our place in the universe. In antiquity people believed the Earth was the centre of the solar system and the universe, whereas now we know we are on just one of many planets orbiting the sun.</p>
<p>But this shift in view didn’t happen overnight. Rather, it took almost a century of new theory and careful observations, often using simple mathematics and rudimentary instruments, to reveal our true position in the heavens.</p>
<p>We can gain insights into how this profound shift unfolded by looking at the actual notes left by the astronomers who contributed to it. These notes give us a clue to the labour, insights and genius that drove the Copernican revolution. </p>
<h2>Wandering stars</h2>
<p>Imagine you’re an astronomer from antiquity, exploring the night sky without the aid of a telescope. At first the planets don’t really distinguish themselves from the stars. They’re a bit brighter than most stars and twinkle less, but otherwise look like stars. </p>
<p>In antiquity, what really distinguished planets from stars was their motion through the sky. From night to night, the planets gradually moved with respect to the stars. Indeed “planet” is derived from the Ancient Greek for “wandering star”. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/5-bJGzLAq58?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The motion of Mars over many weeks.</span></figcaption>
</figure>
<p>And planetary motion isn’t simple. Planets appear to speed up and slow down as they cross the sky. Planets even temporarily reverse direction, exhibiting “<a href="http://www.esa.int/spaceinvideos/Videos/2014/09/ESA_Studio_Retrograde_Motion_No_Dates">retrograde motion</a>”. How can this be explained?</p>
<h2>Ptolemy epicycles</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/117852/original/image-20160407-16263-18tv9uv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/117852/original/image-20160407-16263-18tv9uv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=391&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117852/original/image-20160407-16263-18tv9uv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=391&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117852/original/image-20160407-16263-18tv9uv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=391&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117852/original/image-20160407-16263-18tv9uv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=492&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117852/original/image-20160407-16263-18tv9uv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=492&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117852/original/image-20160407-16263-18tv9uv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=492&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A page of an Arabic copy of Ptolemy’s Almagest, illustrating the Ptolemaic model for a planet moving around the Earth.</span>
<span class="attribution"><span class="source">Qatar National Library</span></span>
</figcaption>
</figure>
<p>Ancient Greek astronomers produced geocentric (Earth-centred) models of the solar system, which reached their pinnacle with the work of <a href="http://www.britannica.com/biography/Ptolemy">Ptolemy</a>. This model, from an Arabic copy of Ptolemy’s <a href="http://www.qdl.qa/en/archive/81055/vdc_100000004884.0x000001">Almagest</a>, is illustrated above. </p>
<p>Ptolemy explained planetary motion using the superposition of two circular motions, a large “<a href="http://www.mathpages.com/home/kmath639/kmath639.htm">deferent</a>” circle combined with a smaller “<a href="http://www.mathpages.com/home/kmath639/kmath639.htm">epicycle</a>” circle. </p>
<p>Furthermore, each planet’s deferent could be offset from the position of the Earth and the steady (angular) motion around the deferent could be defined using a position know as an <a href="http://www2.ups.edu/faculty/jcevans/Equant.pdf">equant</a>, rather than the position of the Earth or the centre of the deferent. Got that? </p>
<p>It is rather complex. But, to his credit, Ptolemy’s model predicted the positions of planets in the night sky with an accuracy of a few degrees (sometimes better). And it thus became the primary means of explaining planetary motion for over a millennium. </p>
<h2>Copernicus’ shift</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/117916/original/image-20160408-23929-w6ijzp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/117916/original/image-20160408-23929-w6ijzp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=685&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117916/original/image-20160408-23929-w6ijzp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=685&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117916/original/image-20160408-23929-w6ijzp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=685&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117916/original/image-20160408-23929-w6ijzp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=861&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117916/original/image-20160408-23929-w6ijzp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=861&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117916/original/image-20160408-23929-w6ijzp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=861&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Copernican Revolution placed the sun at the centre of our solar system.</span>
<span class="attribution"><span class="source">Library of the Congress</span></span>
</figcaption>
</figure>
<p>In 1543, the year of his death, <a href="http://www.space.com/15684-nicolaus-copernicus.html">Nicolaus Copernicus</a> started his eponymous revolution with the publication of <a href="https://www.loc.gov/item/46031925">De revolutionibus orbium coelestium</a> (On the Revolutions of the Celestial Spheres). Copernicus’ model for the solar system is heliocentric, with the planets circling the sun rather than Earth. </p>
<p>Perhaps the most elegant piece of the Copernican model is its natural explanation of the changing apparent motion of the planets. The retrograde motion of planets such as Mars is merely <a href="http://www.esa.int/spaceinvideos/Videos/2014/09/ESA_Studio_Retrograde_Motion_Explanation">an illusion</a>, caused by the Earth “overtaking” Mars as they both orbit the sun.</p>
<h2>Ptolemaic baggage</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/117906/original/image-20160407-16293-2s401q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/117906/original/image-20160407-16293-2s401q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117906/original/image-20160407-16293-2s401q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117906/original/image-20160407-16293-2s401q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117906/original/image-20160407-16293-2s401q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117906/original/image-20160407-16293-2s401q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117906/original/image-20160407-16293-2s401q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The original Copernican model has similarities to Ptolemaic models, including circular motions and epicycles.</span>
<span class="attribution"><span class="source">Library of the Congress</span></span>
</figcaption>
</figure>
<p>Unfortunately, the original Copernican model was loaded the Ptolemaic baggage. The Copernican planets still travelled around the solar system using motions described by the superposition of circular motions. Copernicus disposed of the equant, which he <a href="https://books.google.com.au/books?id=RbT1CAAAQBAJ&pg=PA78#v=onepage&q&f=false">despised</a>, but replaced it with the mathematically equivalent epicyclet. </p>
<p>Astronomer-historian <a href="http://owengingerich.com/">Owen Gingerich</a> and his colleagues calculated planetary coordinates using Ptolemaic and Copernican models of the era, and found that <a href="https://dash.harvard.edu/handle/1/4258973">both had comparable errors</a>. In some cases the position of Mars is in error by 2 degrees or more (far larger than the diameter of the moon). Furthermore, the original Copernican model was no simpler than the earlier Ptolemaic model.</p>
<p>As 16th Century astronomers did not have access to telescopes, Newtonian physics, and statistics, it wasn’t obvious to them that the Copernican model was superior to the Ptolemaic model, even though it correctly placed the sun in the centre of the solar system.</p>
<h2>Along comes Galileo</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/117921/original/image-20160408-23938-1eiukl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/117921/original/image-20160408-23938-1eiukl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117921/original/image-20160408-23938-1eiukl2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117921/original/image-20160408-23938-1eiukl2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117921/original/image-20160408-23938-1eiukl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=536&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117921/original/image-20160408-23938-1eiukl2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=536&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117921/original/image-20160408-23938-1eiukl2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=536&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Galileo’s telescopic observations of the planets, including the phases of Venus, demonstrated that planets travel around the Sun.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>From 1609, Galileo Galilei used the recently invented telescope to observe the sun, moon and planets. He saw the <a href="http://www.loc.gov/exhibits/world/heavens.html#obj75">mountains and craters</a> of the moon, and for the first time revealed the planets to be worlds in their own right. Galileo also provided strong observational evidence that planets orbited the sun. </p>
<p>Galileo’s observations of Venus were particularly compelling. In Ptolemaic models, Venus remains between the Earth and the sun at all times, so we should mostly view the night side of Venus. But Galileo was able to observe the day-lit side of Venus, indicating that Venus can be on the opposite side of the sun from the Earth.</p>
<h2>Kepler’s war with Mars</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/117926/original/image-20160408-23929-jox17r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/117926/original/image-20160408-23929-jox17r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=254&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117926/original/image-20160408-23929-jox17r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=254&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117926/original/image-20160408-23929-jox17r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=254&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117926/original/image-20160408-23929-jox17r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=320&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117926/original/image-20160408-23929-jox17r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=320&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117926/original/image-20160408-23929-jox17r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=320&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Johannes Kepler triangulated the position of Mars by using observations of Mars when it returned to the same position in its orbit.</span>
<span class="attribution"><span class="source">University of Sydney</span></span>
</figcaption>
</figure>
<p>The circular motions of Ptolemaic and Copernican models resulted in large errors, particularly for Mars, whose predicted position could be in error by several degrees. <a href="http://kepler.nasa.gov/Mission/JohannesKepler/">Johannes Kepler</a> devoted years of his life to understanding the motion of Mars, and he cracked this problem with a most ingenious weapon. </p>
<p>Planets (approximately) repeat the same path as they orbit the sun, so they return to the same position in space once every orbital period. For example, Mars returns to the same position in its orbit every 687 days. </p>
<p>As Kepler knew the dates when a planet would be at the same position in space, he could use the different positions of the Earth along its own orbit to triangulate the planets’ positions, as illustrated above. Kepler, using astronomer <a href="http://galileo.rice.edu/sci/brahe.html">Tycho Brahe’s</a> <a href="https://www.princeton.edu/%7Ehis291/Mural_Quadrant.html">pre-telescopic observations</a>, was able to trace out the elliptical paths of the planets as they orbited the sun. </p>
<p>This allowed Kepler to formulate his <a href="http://astro.unl.edu/naap/pos/pos_background1.html">three laws of planetary motion</a> and predict planetary positions with <a href="http://scitation.aip.org/content/aip/magazine/physicstoday/article/64/9/10.1063/PT.3.1259">far greater precision</a> than previously possible. He thus laid the groundwork for the Newtonian physics of the late 17th century, and the remarkable science that followed. </p>
<p>Kepler himself <a href="https://books.google.com.au/books?id=774fAQAAIAAJ&dq=kepler+nova+astronomia&focus=searchwithinvolume&q=inhabited">captured</a> the new world view and its broader significance in 1609’s <a href="https://www.library.usyd.edu.au/libraries/rare/modernity/kepler4.html">Astronomia nova</a> (New Astronomy):</p>
<blockquote>
<p>To me, however the truth is more pious still, and (with all due respect to the Doctors of the Church) I prove philosophically not only that the earth is round, not only that it is inhabited all the way around at the antipodes, not only that is it contemptibly small, but also that it is carried along among the stars.</p>
</blockquote><img src="https://counter.theconversation.com/content/60103/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael J. I. Brown receives research funding from the Australian Research Council and Monash University, and has developed space-related titles for Monash University's MWorld educational app.</span></em></p>We take our understanding of the solar system for granted, but it took centuries to figure out. The original writings of Ptolemy, Copernicus, Galileo and others show how they sparked a revolution.Michael J. I. Brown, Associate professor, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/448092015-07-21T10:18:51Z2015-07-21T10:18:51ZNew Horizons brought our last ‘first look’ at one of the original nine solar system planets<figure><img src="https://images.theconversation.com/files/89049/original/image-20150720-12527-w1dc8s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">We got you, Pluto!</span> <span class="attribution"><a class="source" href="http://pluto.jhuapl.edu/Multimedia/Images/Artist-Renderings.php">JHUAPL/SwRI</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Carl Sagan <a href="http://www.cambridge.org/us/academic/subjects/astronomy/astronomy-general/carl-sagans-cosmic-connection-extraterrestrial-perspective">famously said</a> we were the luckiest generation, to be present during the first reconnaissance of the solar system. The New Horizons mission to Pluto completes this half-century project with its stunning images and data. Meanwhile, however, space science has helped change dramatically our notions of solar systems and planets, with Pluto’s status itself the subject of controversy while New Horizons was on its way.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=507&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=507&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=507&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=637&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=637&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88856/original/image-20150717-21052-17flsu8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=637&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">First image of the far side of the moon, courtesy of the USSR’s Luna 3 spacecraft.</span>
</figcaption>
</figure>
<p>I saw the first Soviet image of the far side of the moon in a grainy newspaper reproduction in 1959, and watched a <a href="http://www.jpl.nasa.gov/missions/ranger-7/">Ranger probe</a> hit the moon in 1964, from a black-and-white 10-inch television, picture by picture.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=636&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=636&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=636&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=800&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=800&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89019/original/image-20150720-12543-1m62g2q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=800&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Saturn as seen by Voyager 2 upon approach.</span>
<span class="attribution"><a class="source" href="http://photojournal.jpl.nasa.gov/catalog/PIA03152">NASA/JPL</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>I followed the exploration of the inner solar system, and while in graduate school was an intern at NASA headquarters in 1981 when <a href="http://www.nasa.gov/mission_pages/voyager/overview">Voyager 2</a> encountered Saturn (the video projector failed, and a technician brought in a small, color set for an auditorium full of people).</p>
<p>By then, Pluto had long been axed from the Grand Tour that would have visited all the outer planets. While scientists, no less than the public, reveled in the episodic reports from the two Voyagers and others, the <a href="http://www.nytimes.com/2015/07/19/us/the-long-strange-trip-to-pluto-and-how-nasa-nearly-missed-it.html">friends of Pluto regrouped</a>. In the early 1980s, a wood model of a proposed Pluto explorer spacecraft adorned a hallway at NASA headquarters, its large radio dish oriented up like a giant bowl. A sign of those fiscal times, people started throwing spare change into the dish antenna.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=312&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=312&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=312&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=392&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=392&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88863/original/image-20150717-21073-djnx81.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=392&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">1994 Hubble Space Telescope image of Pluto and its moon, Charon.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/1994/17/image/a/">Dr R Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>But, about that time, exciting astronomical observations and theory began to reveal the Pluto neighborhood. First, a companion moon, then more, and also discoveries of individual bodies in that remote part of our solar system. As it got more crowded, the almost underground murmurs among astronomers that had for decades suggested Pluto was not in fact the missing “Planet X” believed to have been found in 1930 grew louder.</p>
<p>At one astronomical meeting, I sat near Clyde Tombaugh, discoverer of Pluto, when its planetary status was challenged. Tombaugh, then in his 90’s, jumped to his feet to defend his charge with characteristic vigor. Ironically, it was in part that challenge to planetary status and the intellectual redefinition of the solar system within which it was embedded that may have shaken loose enough spare change to mount a Pluto mission. Incidentally, a small portion of Tombaugh’s cremains are on the New Horizons spacecraft.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88877/original/image-20150717-21027-1rk5d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Celebrating the success of the Apollo 11 lunar landing mission in the Mission Control Center.</span>
<span class="attribution"><a class="source" href="http://www.nasa.gov/multimedia/imagegallery/image_feature_1718.html">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The boomers are the first generation to witness the <a href="http://www.nasa.gov/pdf/607087main_NASAsFirst50YearsHistoricalPerspectives-ebook.pdf#page=443">initial exploration of our solar system</a> and the last to be taught that standard phrase, “the nine planets.” During the last half-century, scientific research and Cold War politics brought to a head changes in scientific disciplines and organization that had been maturing for centuries.</p>
<p>Astronomers had done their work from afar using large telescopes, and geologists had done theirs up close with other tools. Astronomers saw the big picture and struggled to tease out the details. Geologists and other “earth scientists” crawled over the details and struggled to see the big picture. High-tech science and planetary voyages mixed up these tidy disciplinary lines, as much as they challenged the schemes that had organized our world too simplistically into galaxies, stars, planets and moons.</p>
<p>Cold War politics loosened funds and stimulated astronomy, which needed to get beyond our blurry and filtered atmosphere, and planetary science, which needed to get spacecraft and instruments directly to the planets. While astronomy enjoyed a true revolution in understanding the remote and energetic bodies of the universe, geosciences moved beyond just the earth and morphed into a truly comparative planetary science.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=502&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=502&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=502&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=631&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=631&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89028/original/image-20150720-12536-z9rr2l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=631&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">We’ve come a long way from Earth at the center of it all.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Cellarius_ptolemaic_system_c2.jpg">Johannes van Loon</a></span>
</figcaption>
</figure>
<p>Reporting his first telescopic observations in 1610, Galileo remarked that watching sunrise over the mountains of the moon from Venice must look much the same as watching sunrise over the mountains of Bohemia from the moon. The issue of Copernicanism at the time is often phrased as whether the Earth or the sun is the center.</p>
<p>The sleeper issue that would take another four centuries to mature, however, was really about worlds and planets. Galileo and his immediate successors realized that all the planets were worlds in themselves, kin to our previously unique world, and could all be studied in similar ways. While telescopes did get better and better over the next four centuries, only the very largest planets and moons could be observed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=377&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=377&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=377&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88876/original/image-20150717-21047-1df8np6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&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 solar system as we’ve traditionally thought about it.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Solar_sys.jpg">NASA</a></span>
</figcaption>
</figure>
<p>Our simplistic diagram of nine planets in largely empty space circling a sun has yielded to a hugely complex and subtle collection of bodies of every size, interacting with one another, sometimes traveling widely, and kin to the one we call home. This is the completion of the Copernican revolution. It extends from gigantic and exotic worlds like Jupiter to the molecules and chemistry of the life that gives rise to our curiosity. To <a href="http://www.penguinrandomhouse.com/books/159730/cosmos-by-carl-sagan/">paraphrase Sagan</a> again, we are a part of the universe that has evolved to contemplate and study the rest.</p>
<figure>
<img src="http://www.nasa.gov/sites/default/files/thumbnails/image/pluto-observations-through-the-years.gif">
<figcaption><span class="caption">Animation of Pluto observations from 1930 to 2015.</span> <span class="source">Lowell Observatory and NASA</span></figcaption>
</figure>
<p>The entire New Horizons mission over 15 years cost about <a href="http://solarsystem.nasa.gov/missions/profile.cfm?MCode=PKB&Display=ReadMore">US$700 million</a>, or $47 million per year – less than Americans <a href="http://www.bea.gov/iTable/iTable.cfm?ReqID=21&step=2#reqid=21&step=9&isuri=1&2103=70">spend on soft drinks</a>. All of space exploration is but spare change, and this mission’s tariff almost invisible on <a href="http://www.lpi.usra.edu/exploration/multimedia/NASABudgetHistory.pdf">anybody’s ledger</a>.</p>
<p>Like the Romans, we demanded bread and circuses during the space program’s heyday in its first decade or so. This circus is already quite a bargain. Throw some spare change into the next model of an orphan mission of exploration. You will need to have patience, but you will be rewarded.</p><img src="https://counter.theconversation.com/content/44809/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joseph N Tatarewicz has received funding from the NASA History Office and from the Smithsonian Institution for work on which some of this contribution is based.</span></em></p>In the long lead-up to our ultimate flyby of Pluto, space science has reconfigured our notions of what it means to be a solar system, a planet, a world.Joseph Tatarewicz, Associate Professor of History, University of Maryland, Baltimore CountyLicensed as Creative Commons – attribution, no derivatives.