Illustration of the total solar eclipse on 18th July 1860. At top the disc of the Moon is covering the disc of the Sun so that only the Sun's corona (atmosphere) is visible. At bottom are reproductions of solar prominences, or flares, seen during the eclipse. The moment of totality lasts for only a few minutes. Total solar eclipses usually occur less than once a year and can only be seen from a small area of the Earth's surface.