Total solar eclipse. Digitally enhanced composite of 22 images of the total solar eclipse of 11 August 1999. The solar corona (white) has been enhanced, highlighting outlying waves and filaments. The solar corona, which is not normally visible, is the Sun's outermost and hottest layer. The image also shows the Moon emitting a faint glow. This is caused by doubly reflected sunlight, the phenomenon known as Earthshine. Earthshine is caused by sunlight reflecting off Earth onto the Moon and back to Earth. Eclipses occur when the Moon passes between the Earth and the Sun, and casts its shadow across the Earth.