Solar eclipse. Total solar eclipse seen at 8h00 over trees. 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), 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 very high temperature. Photographed during the total solar eclipse of 26 February 1979 seen from the Dalles in Oregon, USA.