See also occulation . Solar eclipses occur when the Moon passes directly between the Sun and the Earth. Partial solar eclipses occur when the alignment is not perfect. Annular eclipses occur if the Moon passes directly between the Earth and the Sun but it is at the furthest point of its orbit, so it does not quite cover the Sun. In this case an annulus of sunlight remains and the corona becomes strikingly visible around the silhouette of the Moon.
Eclipses can also occur outside the solar system in eclipsing binary star systems.
Eclipsing binary . The result of this is that the combined light of the stars varies and give the binary the appearance of a variable star. A good example of this is the star Algol in the constellation of Perseus. The two components in this system orbit one another with a period of 2.87 days. Being a star visible to the naked eye means that even casual observers can see when the Algol system is in eclipse because it is noticeably dimmer in the night sky.