Making a Pinhole Projector to View Solar Eclipses

Annular Eclipse 

A pinhole projector is a simple device that can be a fun project to do with kids, and has very little cost associated with it, and with it you can view partial and annular solar eclipses, and observe large sunspots, or regions of the sun that are slightly cooler and appear darker against the disc of the sun. The whole project should take about 15 minutes to do. If you need a refresher on the types of eclipses have a look at this article for a gentle introduction.

The photo below shows a sunspot group on the sun during a partial solar eclipse (note that the edge of the lunar disc isn't smooth owing to the lunar mountains and valleys).

Solar eclipse with sunspot group

Materials

To make a pinhole projector you'll need the following materials:

  • One shoe box, or similarly sized box with a lid.
  • 4" piece of aluminum foil.
  • Scotch tape.
  • 1 piece of white paper.
  • A large sharp needle.
  • Razor knife or craft scissors for cutting.

After you're done, you should have a device that looks something like this diagram:

Pinhole Projector

 

Construction Instructions

  1. Remove the lid of the shoebox and cut a rectangular hole on one end that's about 1/2" from the two sides and one end as shown above. You'll be looking through this hole to view the projected image of the eclipse, but the exact size of the opening isn't super important.
  2. Next, set the lid of the box aside and cut a hole that's about 1" square in one end of the box.
  3. Take a piece of aluminum foil that is large enough to completely cover the hole you just made in the end of the box. Lay the foil on a cutting board and carefully poke a hole in the center using the needle.
  4. Tape the foil over the hole on the end of the box, taking care to cover the entire opening.
  5. Cut a piece of white paper to fit on the inside end of the box opposite the foil covered hole. Glue or tape it in place. This will be the projection screen where the image will appear.
  6. Place the lid on the box as shown above.

Using the Projector

To use the projector, take it outside on a cloudless day and point the end of the box with the foil toward the sun while watching the inside of the box screen through the hole in the lid. You should see the disc of the sun on the screen looking like a round bright circle, and if there are any large sunspots you should see them on the bright disc. 

Adjusting the Aperture

If the sun's disc is too faint, you can try increasing the diameter of the hole in the foil. Making the hole larger will make the image brighter, but it may appear slightly blurry. A smaller hole should make the image sharper but dimmer, so you may have to play with different sized holes to get an image that you're happy with.