Johann Franz Encke

Johann Franz Encke (; 23 September 179126 August 1865) was a German astronomer. Among his activities, he worked on the calculation of the periods of comets and asteroids, measured the distance from the Earth to the Sun, and made observations of the planet Saturn. Biography Encke was born in Hamburg, where his father was the Pastor at St. James' Church, Hamburg. He was the youngest of eight children, and at the time his father died, when he was four years old, the family was in straitened circumstances. Thanks to the financial assistance of a teacher, he was able to be educated at the Gelehrtenschule des Johanneums. He studied mathematics and astronomy from 1811 at the University of Göttingen under Carl Friedrich Gauss, but he enlisted in the Hanseatic Legion for the campaign of 1813–1814, serving as a sergeant in the artillery of the Prussian army, in Holstein and Mecklenburg. In 1814 he resumed his studies at the University, but after Napoleon's escape from Elba he returned to the military, serving until 1815 by which time he had become a lieutenant. Having returned to Göttingen in 1816, he was at once appointed by Bernhardt von Lindenau as his assistant in the observatory of Seeberg near Gotha (he had become acquainted with von Lindenau during his military service). There he completed his investigation of the comet of 1680, for which the Cotta prize was awarded to him in 1817 by judges Gauss and Olbers. He correctly assigned a period of 71 years to the comet of 1812, now known as 12P/Pons-Brooks. Following a suggestion by Jean-Louis Pons, who suspected one of the three comets discovered in 1818 to be the same one already discovered by him in 1805, Encke began to calculate the orbital elements of this comet. At this time, all the known comets had an orbital period of seventy years and more, with an aphelion far beyond the orbit of Uranus. The most famous comet of this family was Comet Halley with its period of seventy-six years. Therefore the orbit of the comet discovered by Pons was a sensation, because his orbit was found to have a period of 3.3 years, so that the aphelion had to be within the orbit of Jupiter. Encke predicted its return for 1822; this return was observable only from the southern hemisphere and was seen by Carl Ludwig Christian Rümker in Australia. The comet was also identified with the one seen by Pierre Méchain in 1786 and by Caroline Herschel in 1795.