Looking directly at the sun is extremely dangerous: irreversible damage to the eye occurs in just seconds. A solar eclipse can be viewed directly only when the sun is 100% blocked (this phase, called totality, only lasts 2m40s in Goreville). During the rest of the eclipse, which can last several hours as the moon slowly passes in front of the sun, precautions and special viewing devices must be used to see the eclipse. A partial eclipse, which does not reach totality, is also a spectacular sight when viewed safely and will be visible on August 21, 2017 through a large part of North America.
The solar eclipse can be safely viewed by looking at a projected image of the sun. A small hole in a piece of foil acts much like a lens, focusing the sunlight and creating an image which can be projected onto a flat surface for viewing. A device that uses a small hole to create an image is called a pinhole viewer, and can be made with common items around the house at little or no cost. The further away the flat projection surface is from the pinhole, the larger the image will be. Do not look at the sun directly through the pinhole in the foil. Only use pinhole viewers when they are fully assembled and with your back to the sun.
One way to make a pinhole viewer is to modify a long tube. In this demonstration, we use a 48 inch mailing tube. You could also use wrapping paper tubes or items such as Pringles cans with the ends cut off and taped together at the end. Longer tubes will result in larger projected images to view. Tubes can be very long which makes them slightly more difficult to aim without practice, but the projected images tend to be much larger than using a box.
One end of the tube should be covered with a thick material; this will serve as the projection surface to view the image on. The other end of the tube should be open. Mailing tubes come with plastic plugs on the ends, but if you use a wrapping paper tube, cover one of the ends completely with a piece of cardboard or several layers of index cards and tape into place. If you are using a mailing tube, you may remove one of the two plastic plugs and discard the plug to have an open end.
About an inch from the completely covered end of the tube, cut a square hole about 2x2 inches in size; this is the view hole to view the image at the covered end of the tube. On the other open end of the tube, completely cover the opening with foil and tape into place. Use a small pin, needle, or thumb tack to make as tiny of a hole as possible in the center of the foil. You now have a completed pinhole viewer.
Aiming the tube at the sun takes a bit of practice even for adults, but older children are able to use the tube pinhole viewer easily after practice. Younger children may need the tube held for them. Try to use your pinhole viewer before the day of the eclipse to learn how to aim it quickly. To begin, stand with your back facing the sun and place the tube over your shoulder so that the view hole is in front of you and the aluminum foil end is behind your back. Look at your shadow on the ground, and locate the shadow of the tube.
To project an image onto the projection surface at the end of the tube the sun, pinhole, and projection surface must all align in a straight line. We use the shadow of the tube to help us do this. The sun, pinhole, and projection surface are aligned when the area covered by the shadow of the tube is smallest. Move the tube around on your shoulder to make the shadow smaller.
When the shadow of the tube is at its smallest, it will look like a circle attached to your arm's shadow. Once you have the shadow as small as you can make it, look into the view hole which should be near your face, and you should be able to see an image of the sun on the projection surface (closed end of the tube). The 48 inch tube makes an image about a centimeter across, about the size of a dime and large enough to easily pick out different features of the eclipse.
Another easy method to make a pinhole viewer is to use a long box. Here we demonstrate with a cereal box, but any box will work, and longer boxes will result in larger projected images to view. Boxes tend to be shorter than tubes, which makes them easier to aim, however the projected image will typically be smaller than using a tube.
Open the top of the box, remove the short flaps completely, and cut 1.5-2 inches off both ends of each long flap. Tape the remainder of the long flaps together. Place aluminum foil over one end of the box so that it covers one of the holes completely, and tape the foil into place. Use a small pin, needle, or thumb tack to make as tiny of a hole as possible in the center of the foil. The other open side becomes the view hole to look into to find the image of the sun.
The box pinhole viewer is quite easy to aim at the sun, and elementary-aged children can often aim box pinhole viewers on their own. Simply turn your back to the sun, and face the end of the box with the foil and the hole. Aim the pinhole viewer at the sun behind your back; the foil will reflect the most light when you have aimed the box correctly. Look into the open view hole in the box and you will see a small projection of the sun. A regular-sized cereal box makes an image about 3 millimeters across, large enough to see the main features of the eclipse.