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What Are Sunspots?
In this image taken yesterday by the Solar and Heliospheric Observatory, the sunspot group named 687 is about 10 times wider than Earth.
Credit: SOHO/NASA/ESA

For most of us, the idea of spots on the sun seems a bit odd. After all, the sun is that intensely bright and hot star in the heavens, and doesn't seem like something that would be likely to have spots on it. Then again, the spots on the sun aren't like the spots on a Dalmatian or a Bettie Page bikini.

Sunspots are actually "cold" areas on the surface of the sun though cold is a relative term. Sun spots average around 5,000 to 7,500 degrees Fahrenheit (2,760 to 4150 degrees Celsius), in contrast to the areas surrounding them which average around 9,900 F (5,480 C).

Sunspots are caused by magnetic storms in the sun's atmosphere which inhibit the transfer of heat between the layers of the sun (in a process called convection).

There are two distinct parts of a sunspot: a dark central spot called the umbra, and a slightly lighter section around it called the prenumbra, according to "Van Nostrand's Concise Encyclopedia of Science."

Sunspots tend to appear in pairs and are only temporary. Some of the smaller ones (a few thousand miles wide) may last less than a day, while larger ones may last a week or two.

Sunspots have been noted since ancient times, though it wasn't until 1610 that Galileo Galilei scientifically analyzed them. Increased sunspot activity (like increased solar flares) correlates with the solar cycle, so the number of sunspots present at a time peaks about every 11 years.

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