In case you haven’t heard, there’s a solar eclipse coming! But while eclipses are cool, unless you’re in the path of totality — i.e., the part of the country where the Moon will completely obstruct the Sun — you’ll need to take some safety precautions to safely view the eclipse. (Even then, you’ll still need to wear glasses before and after the moments when it’s totally blocked.) After all, just because part of the Sun is covered doesn’t mean you should look directly at the uncovered part of it. Eclipse glasses are a good way to go, but counterfeit models are making rounds on sites like Amazon. Plus, even if you buy certified ones, they might not make it to you in time.
Fortunately, there’s another option: a pinhole projector. Putting together a pinhole projector is about as easy as it gets, and while it doesn’t quite have the same “wow factor” as looking directly at the partially blocked Sun, it’ll still let you safely view what’s happening without potentially going blind.
There are many ways to make a pinhole projector, but you really just need two things: something with a pinhole in it, and something to project the image on.
If you’re in a rush or on a budget, just take two stiff pieces of paper (paper plates or card stock tend to work well, but even regular printer paper should do the job) and poke a pinhole in one with a pin. If you’re really in a pinch, you can even make a pinhole projector by just curling your fingers to only let a pinprick of light through.
How to use it
Now that you’ve got your piece of paper with a pinhole, hold it up and let the sunlight shine through it. Then, using your second piece of paper (or a wall) as a screen, you’ll be able to see an image of the partially obscured Sun, all without burning out your retinas.
As a safety note: you want to look at the projection created by the pinhole on the wall, so keep your back to the Sun, and look at the image created by the light shining through. Do not look at the Sun directly through the pinhole.
Bonus round: the physics of pinhole projectors
Now that you’ve got your eclipse-viewing plans sorted out, here’s how this device works. Pinhole projectors take advantage of a bit of optical physics known as the camera obscura effect.
Generally, light travels in straight lines. So when an object is illuminated, light will continue to bounce off it in a straight line. The pinhole only lets a small amount of those reflections through, allowing an image to form (inverted) on the other side of the hole. This is similar to how lenses work.
It’s the same basic process with the eclipse — except the lit objects are the Sun and the Moon, the “lens” is a piece of paper with a hole in it, and the screen is whatever surface you project it onto.
At the end of the day, a pinhole projector is a fun, quick project for you (or your kids) to view the eclipse. If you really want to take advantage and enjoy the full experience, however, here’s a guideline to make sure you are ordering a pair of certified solar filter glasses that will let you safely see the eclipse directly.
Update, August 18th 12:00pm: This post was originally published on August 9th and has been updated to include video