Bessel, Friedrich Wilhelm (redirected from Friedrich Bessel)

Bessel, Friedrich Wilhelm (frēd`rĭkh vĭl`hĕlm bĕs`əl), 1784–1846, German astronomer and mathematician. He became (1810) director of the new observatory at Königsberg and professor of astronomy at the Univ. of Königsberg. Among his many achievements the most noted is his discovery of the parallax of the fixed star 61 Cygni. Announced in 1838, it was officially recognized in 1841 as the first fully authenticated measurement of the distance of a star. His observations had, by 1833, increased the number of accurately cataloged stars to 50,000. This work was continued and extended by his pupil Argelander. Through observing the variations of the proper motions of Sirius and Procyon, he concluded that they possessed dimmer companions, which was verified a century later by astronomers. Bessel's works on astronomy include Fundamenta Astronomiae (1818) and Astronomische Untersuchungen (1841–42). Bessel also introduced a class of mathematical functions, named for him, which he established as a result of work on perturbation of the planets and which are widely used in applied mathematics, physics, and engineering.

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Bessel, Friedrich Wilhelm

Bessel, engraving by E. Mandel after a painting by Franz Wolf

(credit: The Bettmann Archive)

(born July 22, 1784, Minden, Brandenburg—died March 17, 1846, Königsberg, Prussia) German astronomer. He was the first to measure (by means of parallax) the distance to a star other than the Sun. One of his major discoveries was that the bright stars Sirius and Procyon make tiny motions explainable only by the existence of invisible companions disturbing their motions. His observation of tiny irregularities in the orbit of Uranus, which he concluded were caused by an unknown planet beyond, led to the discovery of Neptune. His mathematical functions for studying planetary motions became widely used in solving a wide range of differential equations.

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Bessel, Friedrich Wilhelm 

Born July 22, 1784, in Minden; died Mar. 17, 1846, in Königsberg. German astronomer; member of the Berlin Academy of Sciences (1812).

When he was 20 years old, Bessel calculated the orbit of Halley’s comet. In 1806, he obtained the position of assistant in a private observatory in Lilienthal. There he reinterpreted the data of J. Bradley’s observations, from which he determined constants of refraction, precession, and nutation that surpassed in accuracy all previous determinations. In 1810 he became a professor at the University of Konigsberg and built an observatory there, which he directed until his death. On the meridian circle of this observatory, Bessel performed observations of 75,011 stars between +47° and-16° declination. Bessel developed a theory of errors of astronomical instruments and discovered the presence of personal bias—that is, the systematic error introduced by a given observer. In the treatment of his observations, Bessel applied the theory of probability and the method of least squares. In 1838, using a heliometer, he determined the parallax of the star 61 Cygni, having measured the distance to fixed stars in this manner. He developed a theory of solar eclipses and determined the masses of planets and the constants of Saturn’s satellites.

Bessel’s work in geodesy was also of great value. In particular, together with J. Bayer he carried out triangulation in East Prussia and, on the basis of the ten best degree measurements, determined the elements of the terrestrial spheroid. He invented an instrument for measuring the base line.

In mathematics, Bessel’s name is given to the so-called cylinder functions of the first kind and the differential equation which they satisfy, an inequality for the coefficients of the Fourier series, and also an interpolation formula.

WORKS

Abhandlungen . . . , vols. 1–3. Leipzig, 1875–76.
In Russian translation:
Populiarnye chteniia o nauchnykh predmetakh. Moscow, 1859.

REFERENCE

Clark, A. Obshchedostupnaia istoriia astronomii ν XIX stoletii. Odessa, 1913. (Translated from English.)