Unfortunately I won't be in a state where I can see the annular eclipse on Sunday May 20th, but hopefully some of you will be. Not sure? Check these animated maps and if your state shows up on the maps page you will be able to see at least part of the eclipse!
So why is it called an annular eclipse? The word annular means ring and is referring to the ring of sunlight that is left around the Sun during the eclipse. You see, for these types of eclipses the Earth-Moon-Sun geometry is such that the apparent size of the Moon is not large enough to totally block out all of the Sun's disk. If you look at my previous blog post you will see that the distance between the Earth and the Moon varies, and so does the distance between the Earth and the Sun (the Earth is also in a non-circular or eccentric orbit). The distances for the May 20th 2012 eclipse are such that the size of the Moon's disk in the sky due to these relative Earth-Moon and Earth-Sun distances is not enough to block out the entire solar disk. So why don't we have some kind of a solar eclipse every month when the Sun-Moon-Earth all line up. The reason is that there is a 3rd dimension called inclination. While the Sun-Moon-Earth may indeed form a line every month they are not always in the same plane with each other each time they form that line. The Moon is inclined to the ecliptic plane (a reference plane in our solar system) 5-degrees as compared to the Earth. That means that the Earth-Sun-Moon are only lined up in this plane twice per orbit. So the Moon always casts a shadow back towards the Earth each month when the 3 bodies line up, but that 5-degree difference in inclination causes the Moon's shadow to miss the Earth unless the Earth and Moon are at one of the two points in the orbit around the Sun (these points are called nodes) where the planes cross.
So if you are lucky enough to be in a state where the eclipse is visible get out and SAFELY enjoy the view. DO NOT look at the eclipse unless you have the proper equipment. If you have no equipement at all and can't find a local astronomy club to view with, check out this NASA site for a list of safe do-it-yourself viewing methods. Even if you have nothing, at least go out and look around at the landscape during the eclipse. The very noticable darkening outside alone is worth experiencing. Enjoy!