Argelander, Friedrich Wilhelm August (1799-1875) was a Finnish-German astronomer and professor of astronomy who compiled the Banner Durchmusterung, a catalog which recorded the positions and magnitudes of 324,198 stars of the northern celestial hemisphere.
Argelander was born in 1799 in Memel, Prussia (now Klaipeda, Lithuania). He was the son of a wealthy Finnish merchant and a German mother and was educated at the University of Königsberg (now Kaliningrad State University). He became interested in astronomy as a student of German astronomer Friedrich Wilhelm Bessel.
In 1820, Argelander became an assistant to Bessel, director of the Königsberg Observatory. In 1836, Argelander was appointed professor of astronomy at the University of Bonn. There Frederick William IV, who became king in 1840, built Argelander a superb observatory where he continued the work of determining the positions of stars that Bessel had begun at Königsberg.
In 1837, he published the book Concerning the Peculiar Movement of the Solar Systems Deduced from the Proper Motions of the Stars. Argelander's primary contribution to astronomy was his Bonner Durchmusterung (3 volumes, 1859-1862), the largest and most comprehensive of prephotographic catalogs. This catalog, with accompanying charts, recorded the positions and magnitudes of 324,198 stars of the northern celestial hemisphere. Magnitude is the scale used by astronomers to measure the brightness of objects in space. The brighter a star, the lower its magnitude number.
In 1863, he became cofounder of the Astronomische Gesellschaft, whose goal was the complete survey of the celestial sky.
Argelander was a major influence on variable star astronomy, the study of stars that vary in brightness, and on the study of a type of star movement called proper motion. He calculated the motion of the sun in space, he developed a system of magnitudes for describing stars too dim to be seen by the naked eye, and he developed the system still in use for naming various stars.