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Sunspots observation, 1917
Sunspots observation. Sequence of photographs, obtained in 1917, of sunspots (dark areas) on the surface of the Sun. The sequence runs from top to bottom, with the sunspots moving from left to right as the Sun rotates. Sunspots, first observed with telescopes in 1610, are areas of magnetic activity that are cooler than the rest of the Sun's surface. They are massive structures, ranging in size from hundreds of kilometres across to sizes larger than the Earth. Published in 1919 in volume 49 of The Astrophysical Journal.
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