If you live in the US and missed the last total solar eclipse in 2017, good news! You’re about to get another chance. A total solar eclipse will occur across Texas and the Midwestern states on April 8. Remember that during a solar eclipse the shadow of the moon falls on the Earth. When you stand in this shadow, it looks very strange. But also great.
Even if you are not on the path of totality, you can still see something. All continental states will experience at least a partial solar eclipse. (View the map here NASA’s eclipse page.) And do I have to tell you this? Never look at the sun without special glasses, even if it is largely blocked by the moon. Maybe you can get a few more safe solar binoculars before the big event.
But there is another way to watch the solar eclipse without glasses: using a pinhole projector. It’s super simple to make and easy to use. All you need is something flat, like a piece of cardboard. Then you poke a hole in it with a pin. That’s actually it. When light from the sun passes through the hole, it projects an image onto a flat surface (such as a sidewalk).
If you were to do this on a normal day, you would see a circular point of light. You would think that is because the hole is round. But during the solar eclipse you see a crescent shape, caused by the moon passing in front of the sun. It is both great and safe for your eyes.
Actually, that’s not even necessary to make a pinhole viewer: they already exist all around us. If you stand under a tree, the small spaces between the leaves will act as holes to project some small crescent-shaped images. Here’s a photo I took during the 2017 solar eclipse:
Fun with holes
Just for fun, here’s a question for you. Most holes are round (because pins have cylindrical shafts). But what if you replaced the round hole with a square hole? What shape would a round sun project onto the ground? Would it be a circle? Would it be a square? Or maybe it would be one circle! What about a triangular hole? What would happen then?
I actually have one card of PUNCH (Polarimeter to Unify the Corona and Heliosphere) which demonstrates this with three holes: round, triangular and square. To look at.