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Friedrich Bessel

Friedrich Wilhelm Bessel (July 22, 1784 - March 17, 1846) was a German mathematician, astronomer, and discoverer of the Bessel functions.

Bessel was born in Minden, Westphalia and died in Königsberg (now Kaliningrad, Russia). He was a contemporary of Carl Gauss.

Bessel's greatest astronomical achievement was the first successful use of parallax to determine the distance to a star. It had been assumed for some time that this method would be the way that provided the first accurate measurement of interstellar distances, but the difficulties to be overcome were immense. In particular, one had to decide on a star that would be close enough to display a measurable parallax, and then one had to make the very exacting measurement.

Other had tried before, and failed, or produced worthless results. Bessel is generally recognized as the first to succeed. In 1838, he announced that he had measured the distance to 61 Cygni, and gave a figure of 0.314 arcsecond, which given the diameter of the Earth's orbit, gave a distance of about 10 light years. The correct value, according to the best current measurements by the Hipparcos satellite, is 0.28547 arcsecond.

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