On 25th October, we’ll have the opportunity to see one of nature’s most awe-inspiring phenomena: The New Moon passing in front of the Sun to create a solar eclipse. Solar eclipses are among the most spectacular events we can see in the sky. Every year, millions travel to witness total eclipses of the Sun, and tens of millions more have the opportunity to see partial phases over a much wider area. The steady march of the Moon across the face of our star is mesmerising to behold as it reveals the motion of our Solar System in real time. Those who witness it have the opportunity to stand in the shadow of our celestial neighbour.
Solar eclipses can show a wide range of phases.
Photo credit: Tom Kerss
This month’s eclipse is a deep partial, with a maximum magnitude of 0.86. This means that 86% of the diameter of the Sun will be obscured during the moment of greatest eclipse, but this figure is only true from one particular location in Russia. In western Europe and the UK, the maximum magnitude will be lower as we stand closer to the edge of the shadow cast by the Moon. In the UK, magnitudes will fall between about 0.15 (15% obscuration) in the South West of England and 0.36 (35% obscuration) in northern Scotland. Click here to see how the eclipse will appear from your location and when to look out for it. The maximum falls at 11:00am Universal Time, which is the same as Greenwich Mean Time. This is noon British Summer Time, but your local time will vary slightly according to where you are.
This map shows the path of the eclipse shadow and bands of magnitude. London is indicated by the white cross, where the magnitude will be 0.26 at greatest eclipse. In Edinburgh, the magnitude will reach 0.3.
Image Credit: Tom Kerss/Xavier Jubier
It’s remindful of the last solar eclipse to be visible from the UK in June 2021. An annular eclipse over Canada and Greenland created partial phases across much of Europe, and millions witnessed the New Moon take a bite out of the Sun. I viewed the eclipse from London, and although there was some cloud, the greatest eclipse was very clearly seen. Afterwards, I received many emails and messages from people who had perhaps briefly glanced at the Sun through the cloud on that day, and noticed it wasn’t perfectly round.
In June 2021, the UK witnessed a partial eclipse, which was part of a stunning annular eclipse over Canada and Greenland. This photo shows the greatest eclipse in London. The magnitude was 0.32.
Photo credit: Tom Kerss
The Sun is the only object in the sky which demands special attention to safety. Being hundreds of thousands of times brighter than a Full Moon, it is harmful to look at directly. Indeed, it is painful to look at! Trust in your natural aversion to it, because staring directly at the Sun can cause irreversible eye damage. The only exception is during the totality of a total solar eclipse, when it is safe to look directly at the solar atmosphere surrounding the night side of the Moon. All the other phases, including the partial phases we’ll see on the 25th, are far too bright.
Fortunately, there are several safe ways to see the changing shape of the Sun during an eclipse, and the best part is that they are inexpensive or free depending on what you already have at home! You don’t need a telescope or any costly specialist equipment to observe an eclipse, but if you want to see the event directly you will need filters. Eclipse viewers, which allow you to safely look at the Sun, are sold widely – usually at low cost.
Eclipse viewers are usually inexpensive, and allow you to safely view the Sun directly.
Photo credit: Tom Kerss
You should beware of price hikes in the run-up to eclipses. Retailers often inflate the price to cash in on the excitement surrounding the event. Buy your eclipse viewers when there are no imminent solar eclipses in the calendar and then store them somewhere dry until the big day. They have dark, reflective foil ‘lenses’ which filter the intensity of the Sun down to a safe and comfortable level, allowing you to see eclipse phases (and other events such as transits or even very large sunspots.) Naturally, the Sun’s surface appears more or less colourless to us. It is essentially just white. Therefore, any colour you see is created by a layer of coloured film in the eclipse viewer for aesthetic effect.
The phases of the Sun during a solar eclipse can be seen clearly with eclipse viewers, but the colour is not significant, and is instead created with a tinted film.
Photo credit: Tom Kerss
It’s even safer to watch the eclipse indirectly by projecting it. This means making an image of the disk of the Sun. When viewing a projection, you are looking away from the Sun and there is no risk of damaging your eyes. You can build your own solar projector using household items. You’ll need a box, some white card or paper, kitchen foil, scissors, tape and something small and pointy like a paperclip or staple.
Start by cutting a hole in one end of your box. This will be the sun-facing end. Cut a second one on the side of the box, at the other end, allowing you to look at the inside face of the box farthest from the sun-facing end. You can also cut out and attach a piece of white paper or card to the inside, as this will make your eclipse projection appear brighter.
Next measure out a piece of foil that is slightly larger than the hole on the sun-facing end, and using a paper clip or staple, poke a tiny hole in the centre of it. This will be the projection aperture. It works like a pinhole camera.
Attach the foil to the inside of the box behind the sun-facing hole, so it is completely covered. Use tape on all sides. The foil should be free of creases, but it is not necessary to pull it completely taut. This is the last step in building your solar projector.
Now you’re ready to make an image of the disk of the Sun. When you point the pinhole towards the Sun, you’ll see an image of it on the white paper or card. Ordinarily this will appear as a perfect circle, but during eclipses you’ll see crescent phases.
If you don’t have the items you need to make a pinhole projector, don’t worry – you probably have something in your kitchen that will work as an ad-hoc solar projector! A colander or strainer has hundreds of tiny holes that each act like a pinhole projector. If you hold it out during a solar eclipse, you’ll see crescent-shaped spots in its shadow. You can even use the shadows of your hands. Make a grid with your fingers and hold them up. This is a fantastic and safe way to view and share this solar eclipse. I wish you good luck and clear skies on the 25th!
Want to take your first steps into studying the Solar System with a telescope? Discover how to safely view the Sun in detail and forecast future eclipses with Observing Our Solar System: A Beginner’s Guide – available now!
Observing Our Solar System: A Beginner’s Guide is now available from Collins, providing a comprehensive introduction to exploring the Moon, Sun, planets and much more with your eyes, binoculars, and telescopes. Discover the history of Solar System science, the highlights of our neighbourhood, special events and more.
Tom Kerss is an astronomer, astrophotographer, writer and speaker, specialising in the rewarding task of connecting people to their shared universe. He is the author of Northern Lights, Moongazing, Stargazing and You Can Explore the Universe, all of which are available now.
His new book, Observing Our Solar System, is out now.