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Catch the sun: are you ready for a partial solar eclipse today?

A solar eclipse as seen in Albuquerque, New Mexico, in 2012 – similar to what many Australians will see this afternoon (weather permitting, of course). Robert Adams/Flickr, CC BY-ND

Catch the sun: are you ready for a partial solar eclipse today?

Due to a rare alignment of events, many Australians will today experience a second eclipse this month.

A partial solar eclipse will be visible from across Australia later this afternoon, following the total lunar eclipse that was seen two weeks ago, on Tuesday April 15.

Perth and other southern parts of Western Australia will see a good fraction of the sun obscured (at least 59% of the sun’s diameter) and will experience the whole event – from the moment of first contact when the moon approaches the sun, through to greatest eclipse, then more than two-and-a-half hours later, the moon will be seen to part ways with the sun.

The rest of Western Australia along with the Northern Territory will see the entire eclipse too, but a smaller fraction of the sun will be hidden.

Other regions around Australia will see the first half of the eclipse only, as the sun will set while the eclipse is still in progress. It bookends nicely with the total lunar eclipse from earlier in month, when the eclipsed moon, appearing pale red, rose in the east before returning to full brightness as it moved out of Earth’s shadow.

Black hole sun

In areas where the eclipsed sun will be setting, a clear view towards the west will be essential. During the solar eclipse the moon will move across the top left-most part of the sun.

The northern part of Australia will see the smallest eclipse. In Darwin the moon will cover just 10% of the sun’s diameter at the peak of the eclipse.

Southern areas will see more, with Hobart experiencing a maximum of 72% of the sun’s diameter blocked by the moon.

The animation below shows the path of the eclipse shadow (shown as the light shadow) moving across the Earth and racing the setting sun (shown as the dark shadow).

A remote and inaccessible region of Antarctica will experience an annular eclipse, where a ring of sunlight will remain shining out from around the dark moon. In this instance, 99% of the sun’s disc will be covered.

The moon won’t completely cover the sun because at its current position along its orbit, the moon is slightly too far from Earth to perfectly match the sun’s size. Instead, the Earth passes through the moon’s antumbral shadow — a section of the moon’s shadow that extends beyond the darkest part of the shadow, or umbra — creating an annular eclipse.

Today’s eclipse is somewhat of an obscure rarity. The path of a solar eclipse is typically very narrow, but this one only just manages to meet the Earth’s surface. In fact, the centre of the moon’s shadow misses Earth completely.

During an annular eclipse, the moon’s umbral shadow is not long enough to reach Earth and Earth is immersed in the antumbral shadow instead. (Diagram not to scale.) The Conversation

According to American astrophysicist Fred Espenak and Belgian astronomer Jean Meeus, there will be 3,956 annular eclipses across the 5,000-year period spanning 2000 BCE to 3000 AD and only 68 (or 1.7%) of them are non-central or lopsided.

Not only will the annular ring today appear off-centre, but the sun will also sit very low to the Antarctic horizon.

The annular eclipse will occur about 1,000km south-east from Casey Station in the Australian Antarctic Territory. At Casey Station itself, an impressive 96% of the sun’s diameter will be obscured, with just a crescent sun appearing below the dark moon.

View from Australia

The partial eclipse from Australia will result in little or no change to the daytime sky. There’s simply not enough of the sun blocked out to greatly reduce the sky’s brightness. In addition, any small effects will be washed out in areas where the sun is so low in the sky.

Local circumstances for the eclipse from a variety of Australian cities is given below, as taken from the Astronomical Society of Australia’s factsheet on the partial solar eclipse.

Those living elsewhere in the country (or just take a look anyway because it’s an excellent piece of work) can use an online Google map created by French amateur astronomer Xavier Jubier to “zoom and click” onto any location and discover their local timings (provided in Universal Time) for the eclipse and see an image of what to expect at the eclipse’s peak.

See the eclipse without harming your eyes

It is important to stress that you cannot directly observe an eclipse with the unaided eye or sunglasses.

The UK’s partial solar eclipse from October 3, 2005. The image is oriented to match the appearance of today’s Australian eclipse. Phil Hart

This isn’t because the eclipse itself is especially harmful, but because looking at the sun at any time is risking your eyesight due to the sun’s intense UV radiation. Eclipses make it tempting to stare at the sun, and by all means, observe the eclipse, but take the right precautions to so.

These days one of the easiest methods is to purchase inexpensive but specially designed eclipse glasses from reputable telescope and astronomy shops or your local public observatory, science centre or planetarium.

Such organisations, as well as amateur astronomical societies, may also organise viewing events using special solar telescopes or by fitting solar filters to their usual astronomical telescopes.

The best DIY method is to create a pinhole camera. The simplest one involves making a small circular hole (with a nail or tack) in a large piece of cardboard. Do not look through the hole, but allow the sun to shine through and project an image onto a second piece of cardboard.

A very rudimentary, yet effective, pinhole camera. Sid/Flickr, CC BY-NC-ND

A blank wall or a clear patch of ground can also make a good surface for projection. A wall roughly a metre away will produce a tiny image of the sun, but enough to follow the stages of the eclipse. Move the pinhole camera away from the wall and the image will get bigger (but fainter).

Sometimes nature helps out too. If you look at the shadow made by a leafy tree on the ground or a wall (five to 10 metres away), you will often see overlapping circular spots of light. These bright spots are images of the sun, and during the eclipse they will turn into crescents.

Finally, if the weather is uncooperative, then turn to the internet and view the live webcast from robotic telescope service Slooh, which will be broadcasting from Australia.

The next partial eclipse visible from northern and western regions of Australia will occur on March 9, 2016 and the path of totality will cross Sumatra, Borneo, Sulawesi and the Pacific Ocean.

Australia’s next total solar eclipse won’t be until April 20, 2023, and it’s a tough one, only barely touching the Western Australia coast near Exmouth.

But come July 22, 2038, and a total solar eclipse will cross the country and create a spectacular view as it passes right across Sydney.