230 years ago today — March 13, 1781 — British astronomer Sir William Herschel discovered the planet Uranus.
(Uranus and three of its moons. NASA image from the Voyager spacecraft.)
Herschel discovered Uranus by accident while surveying lesser-magnitude stars. Up until that time, Uranus itself was thought to be a star.
This National Air & Space Museum page has more about the discovery of the outer planets of our solar system.
On a more recent space history note, 25 years ago today the European Space Agency’s Giotto spacecraft encountered Comet Halley. It was Europe’s first deep space mission, and the first to return close-up images of a comet’s nucleus.
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