Annular solar eclipse geometry, artwork. Solar eclipses occur when the Moon passes across the Sun as seen from the Earth. The amount of the Sun that is covered by the Moon depends upon the distance of the Moon from the Earth. As the Moon orbits the Earth in an ellipse, its distance can vary. When this distance is too great, the Moon only partially covers the Sun and an annular (ring- shaped) eclipse occurs as the Sun forms a ring around the Moon. An annular solar eclipse happens around once a year and lasts for a few minutes. It is seen in the cone of the umbra (dark shadow, some 100 kilometres wide). The penumbra (light shadow) causes a partial eclipse.