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)
Sunspots can be as big as the Earth.
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 17th century scientist sees blemishes on 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.
George Hale discovers sunspots' magnetic origins.
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.
Images of the Sun are created with a huge solar telescope.
In the late 1960s, images of the Sun are created at Kitt Peak National Observatory with the McMath-Pierce Solar Telescope.
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:
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