Late in the afternoon today, May 20, 2012, half of North America is in for a bit of a celestial show — an eclipse of the sun known as a “ring of fire.” A ring of fire happens when the moon passes in front of the disk of the sun but does not fully cover it, leaving a thin ring of sunlight to escape around the edges of the moon. Where I live in southern Washington state we will miss out on the full ring of fire, but the eclipse will still cover over 80% of the sun’s disk. Just a six hour drive to the south, Medford, Oregon will get the full show, along with Las Vegas and other parts of the Western United States.
Safely viewing an eclipse can be a bit of a trick. The first rule of thumb for any solar viewing is never look directly at the sun. The UV radiation doesn’t do good things for your eyes. This is even more important if you are using any kind of magnifying device, such as a pair of binoculars or a telescope. To understand why, simply remember the childhood trick of using a lens to burn ants on the sidewalk. By pointing a telescope or binoculars at the sun you are pointing a lens at the sun. When you look through that lens without having a properly purchased and installed solar filter your eyeball can easily become the ant, and you can do permanent damage to your eyes.
However, even if you didn’t manage to purchase a pair of eclipse glasses, there is a simple safe way to view the progress of the moon across the sun for anyone, even if you don’t own a telescope or binoculars. All you will need is two pieces of sturdy card stock. In one piece of cardboard use a pin to prick a hole. If you find it difficult to get a clean pin prick, you may choose to cut out a larger circle of cardboard and tape over it a small piece of aluminum foil. Then put the pinhole in the aluminum foil. Now use one hand to point the card stock at the sun. Using the other hand hold the other piece of card stock behind the pinhole. The pinhole acts as your projector, and the second piece of card stock acts as a screen on which you project the image of the sun.
You can see an illustration on how to build a pinhole projector on eclipse.org.uk, which was set up for an eclipse that arrived in 1999. If you do own a telescope but do not own a proper sun filter, you can also create a wonderful projector using the lens of your telescope. Kathy Ceceri has a post on how to do that over at GeekMom.
Whether you build a viewer or not, if you are on the Pacific coast today make sure to notice the dimming of the light between 6 and 7 PM. Just make sure you avoid the temptation to look directly at the sun. The permanent damage to your eyes isn’t worth it.