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Who first noticed sunspots? It's hard to say, as the records left by many ancient peoples have been lost (or not kept in the first place). But as early as 28 B.C., astronomers in ancient China recorded systematic observations of the cycles of what looked like small, changing dark patches on the surface of the sun. And there are some early references to sunspots in the writings of Greek philosophers from the fourth century B.C. However, none of the early observers could explain what they were seeing. What could sunspots be?

Sometimes, strongly held beliefs interfered with the process of understanding. The ancient Greeks, and other Europeans after them, were highly influenced by the teachings of Aristotle, a Greek philosopher who held that the sun and the heavens were ideal, an embodiment of unblemished perfection. So, many early European astronomers who saw sunspots were puzzled. How could there be spots on the sun? As Dearborn puts it, 'That's why, when Galileo turned his telescope on the sun, and said "hmm! there are definitely blemishes on the sun,' it was such a striking discovery."

 

Galileo and the Advent of the Telescope
The earliest astronomers had to rely on their eyes to observe the sun. Given the proper conditions (such as fog or haze or viewing the sun at sunset), it is possible to observe sunspots with the naked eye. Viewing the sun in this way presented a problem, since looking directly at the bright sun is not only hard to do, but very dangerous. You should never look directly at the sun. The sun's radiation contains not only visible light, but powerful ultraviolet radiation as well, which can severely burn your eyes and permanently damage your eyesight.

The invention of the telescope by Dutch craftsmen in about 1608 changed astronomy forever. Suddenly, European astronomers could peer into space, seeing previously unimagined details on known objects like the moon, sun, and planets, and discovering planets and stars never before visible.

 Johannes Hevelius


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Observatory  1998 The Exploratorium.