242 years ago, in 1784:

William Herschel discovers NGC 23, a spiral galaxy in the Pegasus constellation.

168 years ago, in 1858:

George Mary Searle, an American astronomer and Catholic priest, discovers asteroid 55 Pandora.

21 years ago, in 2005:

At the Keck Observatory, Mike Brown and his team discover Dysnomia, a moon of the dwarf planet Eris.

15 years ago, in 2011:

The Delta II 7000H makes its last flight, launching the twin GRAIL probes to create a detailed gravity map of the Moon.