On Thursday this week (10th June) we’re treated to a special celestial event – an eclipse. Eclipses are a regular if infrequent occurrence – a natural result of the movement of the Moon around the Earth.
As the Moon orbits the Earth the three bodies line up every now and again. Because the Moon is 1/400th the Sun’s diameter and 1/400th the distance away the two objects look about the same size on the sky – by sheer fluke! This makes it possible for one to block out the other. Thursday’s eclipse is solar – the Moon is in between the Sun and the Earth, casting a shadow on the Earth’s surface.
As the Moon orbits the Earth, Earth Sun and Moon regularly line up as in the image below.
The Moon completes an orbit of the Earth around every 28 days – however the Moon’s orbit is inclined at an angle of about 5⁰ to the Earth’s orbit around the Sun, which is why eclipses do not occur every month.
Above: Geometry of a solar eclipse – image from ESA
From the UK, this solar eclipse will be partial – as the Moon passes in between the Earth and Sun the three bodies won’t be lined up exactly from our viewpoint, so the Moon will cover just a small section of the Sun. Weather permitting, from the UK it will appear as below (timings are for the location of Jodrell Bank):
First contact – the Moon grazes the edge of the Sun
Precise timings vary depending on your location – check out this page Solar & Lunar Eclipses Worldwide (timeanddate.com) to find the exact timings for where you are (you may see timings in the media for ‘UTC’ which is Coordinated Universal Time and can be considered as the same as GMT).
From some other parts of the world the eclipse will be ‘annular’ – this is where the Moon’s disk doesn’t entirely cover the disk of the Sun (that would be a total eclipse) but leaves a bright ring visible at the moment of maximum coverage. This happens because neither the Earth’s orbit around the Sun nor the Moon’s orbit around the Earth is exactly circular, so that the apparent sizes of the Sun and Moon vary somewhat – this means that sometimes, as in this case, the Moon can look a bit smaller in the sky and so unable to cover the Sun’s disk completely.
For more info about this week’s eclipse check out Annular Solar Eclipse on 10 June 2021 (timeanddate.com) and for a comprehensive guide plus predictions for future eclipses check out MrEclipse.com
Never look at the Sun directly as it can severely damage your eyes. To view the eclipse safely you can either use a pinhole viewer which is super simple to make How to View a Solar Eclipse: Make a Pinhole Projector (timeanddate.com) or – even easier – you can experiment with using things that already have holes in them such as a colander. Just line the colander up with the Sun so that it casts a shadow on the ground and move it towards or away from you until the lines are sharp – during the eclipse you will see lots of crescents as in the picture below.
Above: Image courtesy of Wikimedia Commons : Steve Elliott from UK, CC BY-SA 2.0
These are fun DIY ways to observe but you can also buy special eclipse glasses which allow you to look at the Sun safely – otherwise observation should never be direct as looking at the Sun can severely damage your eyes. In previous years there have been rumours suggesting that you can look at the Sun’s reflection safely in a pool of water – this is untrue and risks eye damage.
In case of cloudy skies there will also be a live stream available here
And if you’re free on Thursday morning and fancy a bit of astronomy with your morning coffee, book a ticket to visit us at Jodrell Bank Discovery Centre where, weather permitting, we will have safe observing by projecting the Sun’s image. As ever, our friendly and knowledgeable engagement team will be on hand to answer your astronomy questions.
Fingers crossed for clear skies!