Total solar eclipse. The large shining corona of the Sun, seen during the total solar eclipse of 11 July 1991 from Baja California, 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's, and consists mainly of slow-moving particles of cosmic dust. The shape of the corona changes during the cycle of solar activity under the influence of the Sun's magnetic field.