The Sun's halo during eclipses is known as the CORONA, which is a Latin word meaning crown or wreath. The CORONA is a white halo of plasma that surrounds the Sun during a total solar eclipse. It is visible only during a total eclipse because it is much fainter than the Sun's photosphere. The CORONA is composed of hot plasma and is much hotter than the surface of the Sun. It is believed to be heated by magnetic fields generated by the Sun's rotation.