Total solar eclipse. Sequence of images of the Sun during a total solar eclipse. Running from centre left to upper right, the sequence shows the disc of the Moon gradually moving over the disc of the Sun, and then moving away again. At totality, the Moon fits perfectly over the Sun and the corona (halo, white), the Sun's atmosphere, becomes visible. It is not visible at other times because of the overwhelming brightness of the rest of the Sun. 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.