US NAVAL OBSERVATORY / SCIENCE PHOTO LIBRARY US NAVAL OBSERVATORY / SCIENCE PHOTO LIBRARY
Sun and sunspots in 1910s, stereoscopic card. These are paired stereoscopic images which provide a 3D image (stereogram) when viewed side-by-side. Sunspots (dark areas) are areas of magnetic activity that are cooler than the rest of the Sun's surface. Image obtained with the 40-inch refracting telescope at the Yerkes Observatory, Chicago, USA. Published by the Keystone View Company.
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