Safely observing the partial solar eclipse

 

On Friday 20th March, the UK will be witness to a rare and beautiful astronomical event – a solar eclipse. Starting at around 8.30am (the exact times vary by a few minutes around the country) the Moon will slowly begin moving in front of the Sun, reaching maximum coverage by about 9.30am. Seen from the UK, between 85% and 95% of the Sun’s disc will be covered by the Moon. Click here to get the exact eclipse details for your location.

From the UK this will be a partial solar eclipse, not a total one where the Sun’s entire disc is obscured. Still, this is the best solar eclipse visible from the UK since the total eclipse of 1999 and we won’t get another one as good as this until 2026! This means it is well worth observing this event – but it’s vital you take the necessary precautions.

Firstly, never, ever, under any circumstances, look directly at the Sun without the proper equipment. Looking at the Sun with your naked eye can cause severe long-term damage. Using binoculars or a telescope to look at the Sun can cause instant permanent damage.

If you want to view the eclipse directly you can buy a solar telescope, or some solar glasses (like the ones modelled above). These contain very strong filters; like ultra-mega-strong-sunglasses. They block out more than 99% of the Sun’s light and only let through a tiny, safe amount. Before you use them though, you must check them every time. Look around you. You shouldn’t be able to see anything, because nothing on Earth is as bright as the Sun. If you can see something, even if it’s just a tiny scratch that’s letting in some light, you can’t use them; they’re not safe. I’m afraid our Jodrell Bank solar eclipse glasses have now sold out on our estore.

You can also observe the eclipse indirectly, by buying/building a sun spotter, or a pinhole camera. There’s lots of information on the web that will tell you how to do this, such as this article from the Royal Astronomical Society & The Society of Popular Astronomy, or this video guide with Dr Lucie Green.

 

Here’s what the eclipse will look like from Manchester…

Why does the Moon block out the Sun during a solar eclipse?

The Moon orbits around the Earth, taking 28 days to do so. This gives rise to the different phases of the Moon that we see on Earth over a month. Once every 28 days the Moon is in front of the Earth; between the Earth and the Sun. This is called the New Moon phase, since the side of the Moon we can see is dark (it’s the opposite side that is being illuminated by the Sun). This is not necessarily a solar eclipse, however.

The Moon’s orbit is not flat around the Earth. Compared to the Earth’s orbit around the Sun, the Moon’s orbit is tilted by 5 degrees above and below it. This means that when the Moon is in its New Moon phase, it usually passes above or below the Sun in the sky. Just occasionally however, the Moon and Sun will line up and the Moon will block out the Sun, causing a solar eclipse.

Solar eclipses cannot be seen everywhere on Earth; you need to be viewing the Moon from the right angle. During a solar eclipse the Moon casts a shadow on some parts of the Earth. If you’re standing under the shadow, you can see an eclipse as it passes over you.

During a total solar eclipse the Moon and Sun line up perfectly as they both appear to be the same size to us. This is often described as a bit of a ‘cosmic coincidence’. The Sun is huge compared to the Moon; 400 times as wide, but the Moon is also 400 times closer to us than the Sun. This makes them look the same size in the sky. This won’t be the case forever though. The distances to the Moon and the Sun are slowly changing. Each year the Earth is getting about 15cm further away from the Sun and the Moon is getting about 4cm further away from us. Best enjoy these solar eclipses whilst we can then, in a few million years they won’t be as good!

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Jamie Sloan is Education Manager at the  Jodrell Bank Discovery Centre