Earth and Space

Spotting sunspots

Stories from Physics for 11-14 14-16 IOP RESOURCES

  • There is evidence of observation of sunspots in ancient Greek and Chinese astronomical records. One of the earliest telescopic observations of the phenomenon was made by amateur father-and-son observers David and Johannes Fabricius in 1610. On David’s birthday, the pair noted dark spots on an image of the Sun projected through a telescope. Johannes published an essay on his discovery, preceding Galileo’s description of sunspots by a year. The pair did not survive to see the impact of their discovery - Johannes died four years later and his father was murdered shortly after by a farmer whom Fabricius had accused of stealing a goose.
  • Whilst to the Earth-based observer, sunspots look like small black spots on the surface of the Sun, their appearance is deceptive as they are perceived in relation to the Sun. Sunspots can have a diameter of up to 100,000 km and have temperatures of around 4,300 K. Seen in isolation, a sunspot would be around a hundred times as bright as the full Moon and only seem dim in comparison to the surrounding surface of the Sun.
  • The Sun’s magnetic field can reverse at times of maximum sunspot activity. In 2001, the solar magnetic field suffered such a change and the reversals are hypothesised to follow the 11-year cycle of sunspot activity.


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