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10-02-2010, 04:13 AM
Solar System (
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Sunspot cycle
About Sunspot cycle

Dark spots appear at places on the Sun where its magnetic field is concentrated. The number of sunspots is controlled by the amount of distortion of the Sun's magnetic field. The magnetic field becomes distorted because the Sun's equator and core rotate more quickly than its other parts. As a result, sunspot activity varies over an average 11-year cycle. Over approximately 11 years, the Sun goes from a solar minimum (fewer spots) to a solar maximum (more spots) and back to a minimum again.

Photo: Sunspots taken by the SOHO probe (NASA/Goddard Space Flight Center Scientific Visualization Studio)

Watch and listen to clips from past programmes TV clips [3] ( ( About Sunspot cycle (

The number of spots on the Sun is not constant. ( Galileo discovers sunspots (

The 17th century scientist sees blemishes on the Sun. ( Spectroscopy reveals the Sun (

19th century astronomers split the Sun's light to see more of its structures. ( Hale explains sunspots (

George Hale discovers sunspots' magnetic origins.

About Sunspot cycle

The solar cycle, or the solar magnetic activity cycle, is the main source of the ~10.7 year periodic solar variation (changing the level of irradiation experienced on Earth) which drives variations in space weather and to some degree weather on the ground and possibly climate change. The cycle is observed by counting the frequency and placement of sunspots visible on the Sun. Powered by a hydromagnetic dynamo process driven by the inductive action of internal solar flows, the solar cycle:

Structures the Sun's atmosphere, corona and wind;
Modulates the solar irradiance;
Modulates the flux of short-wavelength solar radiation, from ultraviolet to X-ray;
Modulates the occurrence frequency of flares, coronal mass ejections, and other geoeffective solar eruptive phenomena;
Indirectly modulates the flux of high-energy galactic cosmic rays entering the solar system.

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