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sunspot
1. A dark patch on the surface of the sun, actually an area of cooler gas, thought to be caused by strong magnetic fields that block the outward flow of heat to the sun's surface.

Sunspots consist of a dark central umbra and a lighter surrounding penumbra. They last from several days to over a month.

2. A dark path on the sun's surface (photosphere) marking the position of a region of intense magnetic field.

A sunspot can be divided into two regions:

  • The central umbra which has a typical temperature of about 4000 degrees Fahrenheit or 2200 degrees Centigrade.
  • The outer penumbra, at about 5500 degrees Fahrenheit or 3000 degrees Centigrade.

The relative coolness of these regions compared to their surroundings produces the dark contrast. Sunspots usually occur in groups, with typical lifetimes of about two weeks.

This entry is located in the following unit: Astronomy and related astronomical terms (page 25)