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Sunspot number is correlated with the intensity of solar radiation over the period since 1979, when satellite measurements became available. The variation caused by the sunspot cycle to solar output is on the order of 0.1% of the solar constant (a peak-to-trough range of 1.3 W·m −2 compared with 1366 W·m −2 for the average solar constant).
Sunspot activity has been measured using the Wolf number for about 300 years. This index (also known as the Zürich number) uses both the number of sunspots and the number of sunspot groups to compensate for measurement variations. A 2003 study found that sunspots had been more frequent since the 1940s than in the previous 1150 years. [30]
A large sunspot group observed in white light. Sunspots are visible as dark patches on the Sun's photosphere and correspond to concentrations of magnetic field where convective transport of heat is inhibited from the solar interior to the surface. As a result, sunspots are slightly cooler than the surrounding photosphere, so they appear dark.
A sunspot this large is easy enough to see from Earth; all that is needed is a solar filter or pair of eclipse glasses to protect your eyes from the sun's dangerous rays. Sunspot AR3664 compared ...
The sunspot activity of December 1610 was the first to be observed using the newly invented telescope, by Thomas Harriot, who sketched what he saw but did not publish it. [12] In 1611 Johannes Fabricius saw them, and published a pamphlet entitled De Maculis in Sole Observatis, which Galileo was not aware of before he wrote the Letters on ...
These have also been used on century times scales but, in addition, instrumental data are increasingly available (mainly telescopic observations of sunspots and thermometer measurements of air temperature) and show that, for example, the temperature fluctuations do not match the solar activity variations and that the commonly-invoked ...
Mercury is visible as a black dot below and to the left of the center. The dark area above the center of the solar disk is a sunspot. The antumbra (from the Latin ante "before" and umbra "shadow") is the region from which the occluding body appears entirely within the disc of the light source.
The solar magnetic field was first detected in 1908 by George Ellery Hale, when he showed observationally that sunspots had strong, bipolar magnetic fields. [1] With these observations, Hale also noted that the majority of sunspot groups within the same northern or southern solar hemisphere shared the same leading polarity and that this pattern reversed across the equator.