ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Galileo's sunspot observations. The Italian astronomer Galileo Galilei (1564-1642) was one of the first people to observe sunspots, using his telescope to do so in 1612. The following year, he published his observations in Istoria e Dimostrazioni Intorno Alle Macchie Solari e Loro Accidenti (History and Demonstrations Concerning Sunspots and their Properties). In this diagram, the sunspots (dark areas) are labelled C, R, and M. Sunspots are areas of magnetic activity that are cooler than the rest of the Sun's surface.
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