Most everyone knows that the Sun is a star, one that looms large in the sky because it is only 150 million kilometers away. But this school lesson was not always accepted as common knowledge. Ancient civilizations viewed the Sun as distinctly different from the stars, and for obvious reasons. The Sun is large and provides warmth, unlike the stars at night, which are tiny, cold points of light from where we view them. The Sun is also very bright and gives off life-sustaining light. This and the fact that it is the most dominant object in the sky made the Sun an object of reverence and worship for many ancient people.

The idea that the stars we see at night are really suns seen across great distances first cropped up in the mid sixteenth century when the Italian philosopher Giordano Bruno suggested that the universe was filled with countless ‘suns’ and that many of these possibly harbored planets, and, perhaps, life of their own. It was for convictions such as these that Bruno was burned alive at the stake in 1600 in Venice.

Once recognized as a star, the Sun quickly assumed a prominent role in stellar astronomy, becoming the best studied star in the sky. What astronomers have learned about the nature of the myriad other stars stems directly from what they have learned about the Sun.

Though it seems relatively stable and quiescent, the Sun is a dynamic, seething sphere of mostly hydrogen gas well over a million kilometers in diameter.