Solar eclipse. Time-lapse image of a total solar eclipse. A total solar eclipse occurs when the Moon completely blocks the Sun's disc causing darkness during the day. The shielding effect of the Moon allows observations of the Sun's outer atmosphere (corona, white), which is normally invisible due to the brightness of the Sun's surface. The corona is a wide layer of very thin hydrogen gas at a high temperature. Photographed during the eclipse of 7 March 1970 over Windsor in North Carolina, USA.