sunspot

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sunspot Region in the Sun's photosphere which is cooler than its surroundings and appears darker. Sunspots vary in size from c.1000 to 50,000km (600 to 30,000mi), and occasionally up to c.200,000km (125,000mi). Their duration varies from a few hours to a few weeks, or months for the very biggest. Sunspots occur where there is a local strengthening of the Sun's magnetic field.

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