Person: Wolf, Johann Rudolf
Rudolf Wolf was a Swiss astronomer and mathematician best known for his research on sunspots.
Mathematical Profile (Excerpt):
 After studying at the Zürich Industrieschule, Wolf attended the University of Zürich where he was taught by Raabe and Gräffe.
 Wolf became director of the Bern Observatory in 1847.
 An observatory was opened at Zürich in 1864, largely due to Wolf's efforts, and he was appointed as director.
 Wolf wrote on prime number theory and geometry, then later on probability and statistics  a series of papers discussed Buffon's needle experiment in which he estimated π by Monte Carlo methods.
 First, however, we discuss Wolf's main contribution which was his study of the 11 year sunspot cycle.
 Wolf, who at that time was in Bern, was fascinated and in 1847 he began his own observational record of sunspots.
 In the following year he devised a system which is now known as 'Wolf's sunspot numbers'.
 Of course an 11 year cycle requires considerable data and Wolf collected not only current data, but data from historic records from 1610 onwards.
 From this data Wolf was the first to calculate an accurate length of the cycle, obtaining a value of 11.1 years.
 Wolf's findings were not well received by his fellow astronomers who argued strongly against his conclusions.
 However Wolf was totally convinced of his discoveries and the validity of his methods, and of course we know that he was right to remain so.
 Wolf conducted experiments throwing the needle 5000 times, obtaining a value of to be 3.1596.
 However, more interestingly, Wolf wanted to show that the method of least squares could be used to estimate the error.
 In this respect, Wolf's paper can be called a forerunner of the Monte Carlo method.
 It is likely that only after 1884 was Wolf aware of the history of the problem, and that Buffon was the first to propose it.
 Wolf also made significant contributions to the history of science.
Born 7 July 1816, Fällanden (near Zürich), Switzerland. Died 6 December 1893, Zürich, Switzerland.
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Tags relevant for this person:
Astronomy, Origin Switzerland
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References
Adapted from other CC BYSA 4.0 Sources:
 O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive