29 September

1951: On 29 September 1951, US astronomer Seth Nicholson discovered Ananke, the twelfth satellite of Jupiter.

As a graduate student at the University of California he was photographing the recently-discovered eighth moon of Jupiter with the 36-inch Crossley reflector when he discovered a ninth. He computed its orbit for his PhD dissertation. At Mount Wilson Observatory, where he spent his entire career, he discovered three more Jovian satellites, including Ananke.