Editor's Note: This article was updated to reflect the upcoming total solar eclipse and to add a newly created video.
The moon will pass directly between the sun and the Earth on Monday, Aug. 21, causing a total solar eclipse. This will be the first total eclipse in 40 years to be visible from the continental U.S., and for the first time in 99 years, the path of totality — when the sun's light is completely blocked by the moon — will travel across the length of the continent.
However, it's extremely dangerous to look at the sun, even if most of its light is obscured by the moon. Just as a magnifying glass can focus enough sunlight onto a leaf to start a fire, the lens in your eye can also focus that sliver of light onto your retina to burn it. And because retinas have no pain receptors, you can permanently damage your vision without even feeling it happen. Let us make this perfectly clear: Don't look at the sun during a solar eclipse!
That's not to say you can't watch it indirectly, though. The best way to view an eclipse is through a simple pinhole camera. To build one, all you need are a few household supplies: a box (a shoe box will work), a small piece of tinfoil, a white sheet of paper, tape, a pin or needle, and a box cutter or X-Acto knife. [Photos show the step-by-step process of making a solar eclipse viewer.]
Here's how to make a solar eclipse viewer 5 easy steps:
Step 1. Cut a small hole (about 1 inch across) in one end of the shoe box, near an edge.
Step 2. Tape a piece of tinfoil over the hole.
Step 3. Using a pin or needle, punch a hole in the center of the foil.
Step 4. Tape a small piece of white paper to the inside of the box, at the opposite end from the foil-covered hole. The paper should be positioned so that light entering the box through the pin hole will hit it. This is where you'll look for the sun.
Step 5. Cut a 1-inch-diameter hole in the box near the image screen (the white piece of paper), but on a different side of the box — the side adjacent to the screen. This is your viewing hole; it must be positioned such that you can look through it at an angle and see the image screen.
When the time comes for the eclipse, hold the shoe box so that it lines up with its own shadow, demonstrating that it is aligned with light from the sun. Stand so that when you look through the viewing hole, you can see a tiny bead of light on the image screen; that's the sun. During the eclipse, you'll see the shadow of the moon pass in front of the sun.
How about an eclipse sun projector with binoculars?
If you're looking for a more high-tech DIY project, and would like to create a projector using binoculars, you can also follow this handy video tutorial: