Like a total solar eclipse, an annular eclipse happens when the moon lines up between Earth and the sun. But in this case, the dark moon's apparent diameter is smaller than the visible disk of the sun, leaving a ring—or annulus—of fiery light around the edges. (See annular eclipse pictures.)

During such an eclipse, "the path of annularity, where the full eclipse will be visible, is hundreds of miles wide and thousands of miles long," said eclipse expert Jay Pasachoff, the Field Memorial Professor at Williams College in Massachusetts.

In this path, "viewers looking through special solar filters can see a ring of sunlight around the black silhouette of the moon," said Pasachoff, who is also a National Geographic Society grantee. (National