- Dark patch seen on the surface of the Sun. Sunspots look dark only because they have a temperature about 2000° lower than the 6000°C of the Sun’s surface. They can be larger than the Earth, and have been known since ancient times because they can become large enough to be seen with the naked eye. (Do not try it, or you risk damaging your sight.) Sunspots are now known to be associated with solar magnetism, whose lines of force give them their shape, and with more general disturbances of the Sun’s atmosphere and surface. They are thought to appear as a result of the Sun’s magnetic field interacting with the rotating gasses of the Sun’s body, and models have been produced on this basis which also encompass the 22-year cycle of sunspot activity and the way in which sunspot activity starts at the Sun’s polar regions and spreads from there towards the solar equator. (See butterfly diagram.) Reversals and weakenings of the Earth’s magnetism are familiar to geophysicists: it is possible that the historical periods of low sunspot activity are a sign that the Sun’s magnetism also varies in some way.
- A region of the sun in which intense magnetic fields are formed. Such an area is slightly cooler and darker than its surrounding surface. Sunspots affect the ionosphere, and can affect radio transmissions. The average sunspot is larger than the planet earth, and the number of sunspots occurring follows cycles lasting approximately 11 years.
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