Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Friedrich Wilhelm Bessel (1784-1846) was a German astronomer and mathematician who is remembered for the functions bearing his name; the Bessel functions of first and second order appear on this German stamp. Bessel was the first to measure the parallax of a star (Cygni 61) in 1838, thus making it possible to calculate its distance. Observing the motions of the stars Sirius and Procyon, he deduced that each was orbiting around another, dark star. These dark stars were later found to be white dwarfs.