Sunspots are dark spots on the Sun caused its magnetic field. The spots are dark because they are cooler than the area of the Sun that surrounds them and are often as big as the Earth.

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 as seen by the SOHO probe (NASA/Goddard Space Flight Center Scientific Visualization Studio)

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About Sunspots

Sunspots can be as big as the Earth.

About Sunspots

The solar cycle or solar magnetic activity cycle is the periodic change in the Sun's activity (including changes in the levels of solar radiation and ejection of solar material) and appearance (visible in changes in the number of sunspots, flares, and other visible manifestations). Solar cycles have an average duration of about 11 years. They have been observed (by changes in the sun's appearance and by changes seen on Earth, such as auroras) for hundreds of years.

Solar variation causes changes in space weather, weather, and climate on Earth. It causes a periodic change in the amount of irradiation from the Sun that is experienced on Earth.

It is one component of solar variation, the other being aperiodic fluctuations.

Powered by a hydromagnetic dynamo process, driven by the inductive action of internal solar flows, the solar cycle:

  • Structures the Sun's atmosphere, its corona and the wind;
  • Modulates the solar irradiance;
  • Modulates the flux of short-wavelength solar radiation, from ultraviolet to X-ray;
  • Modulates the occurrence frequency of solar 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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