Argelander, Friedrich Wilhelm August, ahr guh LAHN dehr, FREE drihkh VIHL hehlm OW gust (1799-1875), was a Finnish-German astronomer, and professor of astronomy at Bonn, Germany. His main contribution to astronomy was his Bonner Durchmusterung (1859-1862). This catalog, with accompanying charts, gave the positions and magnitudes of 324,198 stars of the northern celestial hemisphere. Argelander had 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 was born on March 22, 1799, in Memel (now Klaipeda), Lithuania. Argelander died on Feb. 17, 1875.