Since ancient times, people who are fortunate enough to witness a total eclipse of the Sun have been able to see a remarkable phenomenon with the unaided eye: this feature becomes visible during the short interval of time (no more than 7-8 minutes) when the brilliant light from the photosphere of the Sun is blocked totally by the Moon. When the total eclipse begins, the disappearance of the solar photosphere does not mark the onset of the complete darkness of night. Instead, witnesses see a faint residual brightness in an extended region surrounding the dark side of the Moon. At its brightest, the faint light has an intensity which is no more than 5 × 10−6 times the brightness at the center of the solar disk (van de Hulst, 1950). The faint light is the corona, the Latin word for “crown,” because it appears that the Sun is “wearing” a (faint) covering on top of its brilliant (but hidden) photosphere.