sunspot(redirected from Penumbra (Sun))
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a dark formation observed in the photosphere of the sun. The diameters of sunspots can be as large as 200,000 km, and the temperatures are not greater than 4500°K. Since the temperature of the photosphere is 1,000 to 2,000 degrees higher than that of sunspots, the photosphere is two to five times brighter than the spots. The mean annual number of sunspots varies with a period of 11 years.