What is an annular eclipse?
The annular eclipse of 4 January 1992 seen at sunset from San Diego, California. © Dennis Mammana, 2003. Neither the Moon nor the Earth have perfectly circular orbits. The distance from the Earth to the Sun and from the Earth to the Moon are therefore continuously changing. The further away from the Earth the Sun or the Moon are, the smaller they appear. Although the moon is much much smaller than the Sun, it is also much closer. When seen from the Earth, both the Sun and the Moon appear roughly the same size. When the Sun is closer to the Earth, it will appear very slightly bigger. When the Moon is further from the Earth it will appear very slightly smaller. If the apparent size of the moon is less than the apparent size of the Sun when it passes in front of it, the moon is unable to block the light from the Sun completely, and an annular eclipse occurs. What is seen is a bright ring with a dark centre.
