Solar eclipses are arguably 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.
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 other phases 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.
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.
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 a solar eclipse. Just make sure you have plenty of sunscreen – you might be out there for a while!
Image credit: Joy Ng and Sean Simmons
You can learn all about how eclipses work and how to forecast and observe them in our online course, Stargazing Made Simple. You can even get started completely free by taking a taster course today! Click here to sign up for your FREE stargazing course.