In this month: December
IN THIS MONTH
15th December 1966
Janus, a moon of Saturn, is discovered by French astronomer Audouin Dollfus. Astronomers were first mistaken that another moon, Epimetheus, was the same as Janus. In 1980 Voyager 1 confirmed that these two moons share the same orbit. Janus is potato-shaped with a diameter of 180 kilometres and orbits 151,000 kilometres from Saturn in the gap between the F and G rings, taking 17 hours to complete one orbit. It is extensively cratered with several craters larger than 30 kilometres but has few linear features.
Janus is named after the two-faced Roman god Janus, god of gates, doors, beginnings, and endings. He is usually represented as having one face to look forward and another to look back. Although the name was informally proposed soon after the initial 1966 discovery it was not officially adopted until 1983.
Photograph of Janus by the Cassini mission during its flyby of this Saturnian moon on March 27, 2012. Image Credit: NASA/JPL-Caltech/Space Science Institute
21st December 1968
Launch of Apollo 8 the first mission to take humans to the Moon and back. It was the first crewed spacecraft to leave low Earth orbit, and also the first human spaceflight to reach another astronomical object - the Moon - which the crew orbited without landing. The three astronauts, Frank Borman, James Lovell, and William Anders, were the first humans to witness and photograph an Earthrise. They orbited the Moon ten times over the course of twenty hours, during which they made a