Portrait of Friedrich Bessel (1784-1846), German astronomer. Bessel started his working life as an accountant in Bremen. He made preparations to travel by studying navigation and astronomy. By the age of 26, he was director of the new Konigsberg Observatory. He studied the perturbations of planetary and stellar motions, inventing the Bessel functions to aid his analysis. He was the first to establish the distance to a star by the method of stellar parallax (1838), using 61 Cygni as his first object. He predicted that a small companion star formed a binary system with Sirius, and suggested the existence of the planet Neptune.