ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Sunspot observations, made by the German Jesuit scholar Athanasius Kircher (circa 1601-1680), and published in Ars Magna Lucis et Umbrae (1646). The diagram, accompanied by Latin text, shows the Sun's equatorial region across centre. Sunspots (dark areas), first observed with telescopes in 1610, are areas of magnetic activity that are cooler than the rest of the Sun's surface. Observations of the movement of sunspots allowed early 17th-century astronomers to show that the Sun was rotating, and to estimate its speed of rotation. The Sun's equatorial regions rotate faster than its polar regions.
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