It’s Annular Eclipse Day
There is going to be an annular solar eclipse today! That means the moon will cast a shadow on the earth as it passes between us and the sun while it is at apogee (the furthest distance it gets from earth in its eliptical orbit). This results is a big, black ball with a ring of fire surrounding it. That ring is called an annulus, which is why we call it an annular eclipse.
If the moon were at parigee (the closest distance it gets to earth in its orbit — like it was two weeks ago during the supermoon) and eclipsed the sun, it would be called a total eclipse, because the entire diameter of the moon would block out the sun1.
If you live in California, like I do, go outside this evening at about 5:15 PM and watch. It will peak at about 6:30 PM, and end at about 7:30 PM. Don’t look directly at the sun (at least not for too long)2. NASA’s eclipse website has a cool, interactive map that will show you if and at what time the eclipse will happen in your area. The web page is getting hammered today, but if you give it a while, it should load.
Make A Pinhole Projector
A safe way to view the eclipse is with a pinhole projector. I made the one pictured on this page by cutting out a 10" x 10" piece of foamcore (cardboard will work just as well), cutting a 2" x 2" square out of the center, taping a pice of alluminum foil over the hole, and then poking the center of the foil with a strait pin.
If you hold the projector in front of a white surface at just the right distance, you will project a mirror image of the sun onto the surface. This image won’t burn your retinas. If you want to get a little more elaborate with your viewer, the Exploratorium website has a pretty cool how-to article using a couple of UPS poster tube boxes.
- By coincidence, the moon’s size and distance from us and the sun makes it appear to be the same size as the sun in our sky. ↩
- Have you ever burned leaves with a magnifying glass? The lenses in your eyes are built the same way, and will burn your retinas just like this if you look directly at the sun. You can’t feel it happening because there are no pain sensors back there. ↩