Sunspots
Sunspots
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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Spectroscopy reveals the Sun
Nineteenth century astronomers split the Sun's light to see more of its structures.
By splitting the light of the Sun into its component colours with a technique called spectroscopy, early astronomers saw more of the Sun's features. They also worked out what chemical elements form the Sun.
The Italian physicist and mathematician Galileo Galilei was the first person to observe the Sun through a telescope. He saw sunspots moving across the Sun's surface and realised that it was rotating.
Through careful spectrographic study, early 20th century American astronomer George Hale discovered that sunspots are caused by distortions in the Sun's powerful magnetic field.
In the late 1960s, images of the Sun are created at Kitt Peak National Observatory with the McMath-Pierce Solar Telescope.
About Sunspots
The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in space weather and to some degree weather and climate on Earth. 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, 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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