Of all of the astronomical objects, the Sun is the most important to human beings. Since the dawn of civilization, knowing the daily and annual behavior of the Sun has meant the difference between life and death for people learning when to plant crops and when to harvest. Ancient mythologies preserved this knowledge in story form. These were often picturesque descriptions of the Sun's behavior—for example, the Chinese interpretation of a solar eclipse as a dragon chasing and eating the Sun. Sometimes the stories included precise enough details for predicting solar behavior—for instance, in the version from India, the dragon is sliced into two invisible halves. When the position in the sky of one of these halves is lined up with the Sun and the Moon, an eclipse occurs.

A large, handle-shaped prominence is visible in this extreme ultraviolet imaging telescope (EIT) shot of the Sun...