Sunspots

10.6 - Understand the structure, origin and evolution of sunspots

10.8 - Be able to use sunspot data relating to the solar cycle

Sunspots are areas on the photosphere of the Sun that are cooler than the surrounding area and so appear darker.

Characteristics

Typically they travel around the Sun's disc in groups roughly 1/3 of the surface from 40º north to 40º south of the Equator.

They consist of a central region called an umbra and a surrounding area called a penumbra. Note that these terms are similar to those used in the eclipse section but mean different things.

Temperatures of the umbra are typicaly 4,000k. The penumbra is usually around 5,600k. Typically they vary from a few thousand miles to 50,000km. Exceptionally large sunspots have been observed around 200,000km.

Evolution

Sunspots are caused by local changes in the Sun's magnetic field. They start when coronal loops that eject from the sun and then are drawn back again get 'wound up' as different parts of the sun rotates at different rates. When this happens, they create prominences, sometimes flares, and the chromosphere on the surface gets 'punctured', decreasing the temperature in that area for a time.

Their duration may vary from several hours to months. Sunspots contract and expand as they move until eventually they decay.

Rotation

The rotation of the Sun can be observed because of the movement of sunspots across its disc. See the next page on Rotation.

Sunspot Cycle

Sunspots are good evidence of a solar cycle which the Sun goes through every 11 years.

The more sunspots occur, the more heat the Sun produces and vice versa. More sunspots mean the Sun is active, less mean the Sun is quiet.

 


Animation
Summary
  • Darker part of sunspot = Umbra
  • Lighter part of sunspot = Penumbra
  • Sunspot cycle = 11 years
Questions
  • Why does a sunspot look darker than the rest of the Sun?
  • Describe the long term drift of sunspots.
  • Describe the sunspot Cycle.
Did you know?

A period of very low sunspot activity in the 17th century called the Maunder Minimum coincides with a cold period in northern Europe.

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