On September 23, 1791, German astronomer Johann Franz Encke was born in Hamburg. He studied mathematics and astronomy. The orbits of comets held great fascination for Encke. These couldn’t be seen for many decades at a time before they returned. Because these orbital periods took so long, astronomers were often unsure if “their” comet had been sighted in the past and if so by whom and when.
The great French comet finder Jean-Louis Pons had discovered a new group that seemed to have a much shorter orbital span but he had not calculated their lengths of time. By noting data from four possible previous sightings by other astronomers, Encke worked up calculations for one of these comets and, to the surprise of astronomers used to extremely long orbits, he predicted Pons’ comet would reappear in just over three years’ time! The comet’s return was visible only from the southern hemisphere but its appearance was recorded just as Encke had predicted.
Even more surprising, the comet was immediately called Encke’s Comet, although others, most recently Pons, had actually discovered it. Encke, however, always referred to it as Pons’ Comet.
Suitably, Encke was appointed director of a series of observatories. He instituted public access to his last Berlin observatory. As a professor of astronomy, Encke continued his observations and calculations of comet and asteroid paths and their orbital periods. Eventually he shared a method for determining an elliptical orbit from only three observations.
He received the Royal Astronomical Society’s Gold Medal, twice. In addition to the comet bearing his name, there are also a moon crater, an asteroid, and the 325 km (202 mi)-wide gap within Saturn’s A Ring.
“Encke’s Comet” continues to orbit. It also continues to teach us more about comet life!
B Bondar / Real World Content Advantage