Total solar eclipse. Optical image of the total solar eclipse of 11 July 1991. Solar eclipses occur when the Moon passes between the Earth and the Sun, and casts its shadow across the Earth. They provide an opportunity to observe the solar corona, the Sun's outermost, and hottest, layer (white). Solar flares (pink) can also be seen leaping from the surface of the Sun. Photographed from La Paz, Mexico.