Friedrich Wilhelm Bessel (1784-1846). German astronomer and mathematician, known primarily for making the first accurate measurement of the distance of a star. Bessel oversaw the construction of the Königsberg Observatory and was its director from 1813 until his death. He established the uniform system to calculate the positions of the stars that are still used today.
He was born on July 22, 1784 in Minden, Westphalia (now Germany). From a young age and during his work in Bremen he began to be interested in geography and navigation, considering the problem of the location of ships in the sea. These questions led him to study astronomy, mathematics and begin to make observations to determine geographical length.
In 1804 Bessel wrote a paper on the calculation of the orbit of Halley's comet and sent it to Heinrich Olbers, who at that time was the most expert person on comets. This work impressed Olbers, who published it and recommended Bessel to become a professional astronomer. In 1806 he began working at the Lilienthal observatory, near Bremen. On this site he acquired great experience in planetary observation, especially of Saturn, its rings and satellites.
In 1809 he became director of the New Königsberg Observatory in Prussia and professor of astronomy. He had previously received a doctorate in astronomy from the University of Göttingen on the recommendation of Gauss. While the Königsberg Observatory finished its construction, he continued his work and was awarded the Lalande Prize of the Institute of France for his research on refraction. Bessel undertook the work of determining the position and movement of more than 50,000 stars, which led him to the determination of the parallax of the star 61 Cygni, the first in history, and calculated its distance in 10, 3 years- light.
Bessel designed a reference system for the position of the stars and planets, deduced the errors given by the atmospheric refraction of light, the precession of the earth and other effects. In 1830 he calculated the average and apparent position of 38 stars for a period of 100 years. In 1841 he announced that Sirius had a companion star, which was confirmed ten years later, when calculating the orbit of Sirius B. This star was observed in 1862 by Alvan Graham Clark.
Bessel also noted the irregularities in the Uranus movement, which opened the doors to the discovery of Neptune. In 1817 he introduced the functions of Bessel or cylindrical functions, which he used in gravitational mechanics, but which are applied in other fields such as the propagation of electromagnetic and heat waves. Bessel's functions appear as coefficients in the series of expansion of the indirect disturbance of a planet caused by the movement of the Sun.
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