APOD: 2009 January 25 - Annular Eclipse: The Ring of Fire

APOD: 2009 January 25 - Annular Eclipse: The Ring of Fire

If you'll remember, both the earth and the moon have elliptical orbits, which means that the apparent sizes of the sun and the moon change as the distance between the bodies changes. Since the ellipses are not wildly eccentric, the apparent change is too insignificant to notice without some frame of reference. An eclipse gives us just such a reference. An annular eclipse occurs when the apparent size of the moon is smaller than that of the sun, causing the sun to appear as a ring of fire. This photograph illustrates that point in spectacular fashion.