Bessel, Friedrich Wilhelm (1784-1846)

Friedrich Wilhelm Bessel was the first astronomer who measured the parallax of a star.

Friedrich Wilhelm Bessel was born in 1784, in a small town Minden in North Rhine-Westphalia. In 1804, at the age of 20 has calculated the orbit of Halley's comet based on Thomas Harriot's observation data in 1607. He presented this thesis to Heinrich Wilhelm Olbers, who invited him to be his assistant and later stated this as: I think that my success to enlist Bessel to astronomy is greater value than my entire astronomical work. Bessel's work was characterized by both practical and theoretical research. Not only in astronomy, but he also made his mark in mathematics and geodesy. In 1805, as - proposed by Olbers - Hieronymus Schröter employed him in Lilienthal Observatory near Bremen. In 1809 he was called to the University of Konigsberg to teach, and to manage of the planned observatory.

In 1829, Bessel bought a heliometer from Fraunhofer's company, an equipment to measure small angle distances, usually used to measure double stars. Bessel, however, used it to measure the angular separations of the stars in the constellation Cygnus from each other. Because the stars are in different distances from us, they have different parallaxes. In 1838 as a result of this multi-year measurement series he succeeded to determine the 1/3 degree parallax of 61 Cygni. The result was of great importance, because on the one hand it showed that the stars were enormous distances compared to the size of Earth's orbit, on the other hand it gave a new proof of the Copernican system, and thirdly because it gave a cosmic measuring scale to the hands of mankind. For distance measurement in astronomy this method is still used nowadays. Bessel twice received the most prestigious honor, the Gold Medal of the Royal Astronomical Society in 1829 and in 1841. In 1842 he also got the Kingdom of Prussia's highest award, the Pour le Mérite.  Increases the importance of this achievement that it was not granted to civilians before 1842, only to soldiers.

Three stages of Bessel's career path are reported on a beautifully designed medal. On the obverse Bessel portrait is shown in a half left view, below his signature. On the reverse is an elaborated armillary sphere. In legend around above Bessel's name, birth and death years can be seen. Below the three main station of his life, as it has been mentioned above, the names and the coats of arms of the cities Minden, Bremen and Koenigsberg and can be seen..

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The observatory - destroyed by bombing in 1944 - and Bessel is commemorated on a large, 120 mm diameter cast bronze medal made by medalist Ernst Schomer (1915-2005) in 1984. This year was the bicentennial of the birth of Bessel. On the obverse of the medal half-right facing portrait Bessel is shown. On the left birth and death years, on the right Bessel's autograph is placed. Beneath the artist's initials. On the reverse the observatory's building is located in front of the stars and waning moon background. Below that two year numbers 1874 and 1984 are visible.

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In the early 1920s, the then small town Lilienthal did not forget about famous astronomers. We can find Schröter's portrait and Bessel's and Harding's silhouette on three different denomination necessity notes issued after the first world war. On the top are Bessel's and Harding's name, and the legend below: "Johann Hieronymus Schroeter Ober Amtmann zu Lilienthal von 1782-1816" speaks about Schröter's magistrates and its duration. Below: "DIE LILIENTHALER ASTRONOMEN" i. e. The Lilienthal Astronomers.

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On the reverse of the largest denomination - 75 pfennig - note there is a church and a boat. The inscription: "Die Sparkasse zu Lilienthal gibt diesen Notgeldschein herans zur Ehrung großen Astronomen SCHROETER welcher auf der Sternwarte zu Lilienthal seine bedeutenden astronomischen Entdeckungen machte.", i. e. the Lilienthal savings bank issued this note to honor the great astronomer Schröter whose Lilienthal observatory made possible great discoveries.

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On the reverse of the second note a man is watching a shooting star.

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On the reverse of the third cash astronomical instruments can be seen. On the reverse of the two smaller denomination, we find the same inscription around the rim as on the first one.