Today in the history of astronomy, a photo is shot. The moon Phoebe will be discovered in it months later.
This mosaic of six images from the Cassini flyby of Phoebe showcases the irregular topography and plentiful craters. Credit: NASA/JPL/Space Science Institute
- William Pickering discovered Phoebe, a moon of Saturn, in March 1899, based on photographic plates from August 1898.
- Phoebe’s discovery marked the first instance of a moon being discovered photographically.
- At the time of its discovery, Phoebe was considered Saturn’s outermost moon, though this is now known to be inaccurate.
- Phoebe’s irregular orbit, confirmed by the 2004 Cassini flyby, suggests it is a captured object.
In March of 1899, William Pickering discovered Phoebe, a moon of Saturn, on photographic plates taken on Aug. 16, 1898, by DeLisle Stewart. It was the first moon to be discovered photographically, rather than observationally, and over a hundred years later, it would be the first target of the Cassini spacecraft. Phoebe orbits at a considerable distance from Saturn (about 8 million miles [nearly 13 million kilometers]), far enough that when it was discovered it was believed to be Saturn’s outermost moon. (Today we know there are several smaller moons further out.) Phoebe also has a highly irregular orbit, suggesting it’s a captured object, and observations during the 2004 Cassini flyby bore that out.
