Sunspots: The Sun's Cycle

Penumbra and Numbra in a Sunspot

Sunspots are cooler areas on the surface of the sun that appear to be spots. Sunspots form when the sun's magnetic field comes to the surface. This causes light and heat not to emit efficiently from that location. Normally, sunspots last for only a few weeks. The average sunspot would seem huge to a person standing on the surface of the sun. It is about as big as the average planet. Sunspots run to temperatures of about 2700° F, or 1500° C cooler than most of the rest of the sun. An average sunspot shines as brightly as the full moon. A sunspot is divided into two regions. The penumbra is the warmer, lighter, outer section of a sunspot. The umbra is the cooler, darker area inside central region.

Sunspots occur in a cycle called the "sunspot cycle". This cycle sees the number of sunspots wax and wane. During this cycle the regions where the most sunspots occur changes as well. Sunspots generally appear nearer to the sun's equator when there are more of them. The sunspot cycle lasts around 11 years.

When there are many sunspots the cycle is said to reach its solar maximum. When there are only a couple or no sunspots it is called the solar minimum. From 1645 to 1715 there were very few sunspots. This long period without sunsposts is called the Maunder Minimum after the astrophysisist who discovered it1. It was a bit colder in Europe during this time. The current sunspot cycle started around 1998, reached its peak in 2000, and is now trailing off in 2007.

Outbursts of the magnetic field causes solar flares, which causes auroras. Since outbursts in the magnetic field cause sunspots too, when the sunspots are at solar maximum there are more auroras. Even without the solar flares, a noticeable increase in radiation from the sun occurs during solar maximum.

A pore is a small sunspot that does not have a penumbra. Sunspots usually come in pairs with opposite magnetic polarities. The first written record of an observation of a sunspot comes from China and was made around 800 B.C. Astronomers have also found sunspots on other stars. These are referred to as starspots.

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  1. The Maunder Minimum

Interesting Fact:

The presence or absence of sunspots has been closely tied to the Earth's climate.

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