The large, shining corona of the Sun, seen during the total solar eclipse of 11 July 1991 from Baja Caifornia, Mexico. The visible corona is in fact the overlapping K-corona and F-corona. Usually it is only visible during eclipses, as the light from the Sun's photosphere drowns it out. The K-corona consists of fast-moving free electrons at a temperature of about 2 million Kelvin, at heights of about 75,000km above the Sun's surface. The F- corona extends for many million km, and consists mainly of slow-moving particles of cosmic dust. The shape of the corona changes during the cycle of solar activity under the infuence of the Sun's magnetic field.