Uranus

first planet discovered that was not known in ancient times, named for the god of Heaven, husband of Gaia, the Earth, from Latin Uranus, from Greek Ouranos literally "heaven, the sky;" in Greek cosmology, the god who personifies the heavens, father of the titans.

The planet was discovered and identified as such in 1781 by Sir William Herschel (it had been observed before, but mistaken for a star; in 1690 John Flamsteed cataloged it as 34 Tauri); Herschel proposed calling it Georgium Sidus, literally "George's Star," in honour of his patron, King George III of England.

I cannot but wish to take this opportunity of expressing my sense of gratitude, by giving the name of Georgium Sidus ... to a star which (with respect to us) first began to shine under His auspicious reign. [Sir William Herschel, 1783]

The planet was known in English in 1780s as the Georgian Planet; French astronomers began calling Herschel, and ultimately German astronomer Johann Bode proposed Uranus as in conformity with other planet names. However, the name didn't come into common usage until c. 1850.