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Sunspot numbers have been measured since 1700 and estimated back to 1500. The trend is upward from 1900 to 1960s then somewhat downward [1].
The number of sunspots correlates with the intensity of solar radiation. Since sunspots are dark it is natural to assume that more sunspots means less solar radiation. However the surrounding areas are brighter and the overall effect is that more sunspots means a brighter sun. The variation is small (of the order of 0.1%) and was only established once satellite measurements of solar variation became available in the 1980s. During the Maunder Minimum there were hardly any sunspots at all and the earth may have cooled by up to 1° C (see Little Ice Age).
Apparent references to sunspots were made by first millennium AD Chinese astronomers, who probably could see the largest spot groups when the sun's glare was filtered by wind-borne dust from the various central Asian deserts.
They were first observed telescopically in late 1610 by Frisian astronomers Johannes and David Fabricius, who published a description in June 1611. At the latter time GalileoGalileo Galilei ( Pisa, February 15, 1564 Arcetri, January 8, 1642), was a Tuscan astronomer, philosopher, and physicist who is closely associated with the scientific revolution. His great achievements include perfecting the telescope, a variety of astron had been showing sunspots to astronomers in Rome, and Christoph ScheinerChristoph Scheiner ( July 25 1573 or 1575 June 18 1650) was a German astronomer and Jesuit. He was one of the first to observe sunspots (in 1611), although he took these to be satellites of the Sun. His book Rosa Ursina was published in 1630; by this time had probably been observing the spots for two or three months. The ensuing priority dispute between Galileo and Scheiner, neither of whom knew of the Fabricius' work, was thus as pointless as it was bitter.
Sunspots had some importance in the debate over the nature of the solar systemA generic solar system (or planetary system consists of at least one star and various orbiting objects (such as asteroids, comets, moons, and planets). The term originated to describe the planetary system around Sol, the Latin name for our sun. The planet. They showed that the Sun rotated, and their comings and goings showed that the Sun changed, contrary to the teaching of AristotleAristotle ( Greek Αριστοτλης Aristotelēs) ( 384 BCE March 7, 322 BCE) was a Greek scientist and philosopher. Along with Plato, he is often considered to be one of the two most influential philo. The details of their apparent motion could not be readily explained except in the heliocentric system of CopernicusNicolaus (or Nicholas Copernicus (original name Kopernik or Koppernigk Polish Mikolaj Kopernik German Nikolaus Kopernikus February 19, 1473 May 24, 1543) was an astronomer, mathematician and an economist who developed a heliocentric ( Sun-centred) theory.
Sunspot research was dormant for much of the 17th and early 18th centuries because of the Maunder Minimum, during which no sunspots were visible for some years; but after the resumption of sunspot activity, Heinrich SchwabeSamuel Heinrich Schwabe ( October 25, 1789 April 11, 1875) was a German astronomer. Schwabe was born at Dessau. At first an apothecary, he turned his attention to astronomy, and in 1826 commenced his observations on sunspots. In 1843 he made the suggestio in 1843Events February 6 The first minstrel show in the United States The Virginia Minstrels opens (Bowery Amphitheatre in New York City). February 11 Giuseppe Verdi's opera I Lombardi premieres in Milan May 18 The Disruption of the Church of Scotland took place reported a periodic change in the number of sunspots.
An extremely powerful flare was emitted toward Earth on 1 September 1859. It interrupted telegraph service and caused visible Aurora Borealis as far south as Havana, Hawaii, and Rome with similar activity in the southern hemisphere.
Possibly the powerful flare observed by satellite instrumentation began on 4 November 2003 at 19:29 UTC, and saturated instruments for 11 minutes. Region 486 has been estimated to have produced an X-ray flux of X28. Holographic and visual observations indicate significant activity continued on the far side of the Sun.