Yesterday marks 240 years since William Herschel discovered Uranus.

The seventh planet was officially discovered on March 13, 1781. But Herschel wasn’t really the first to spot this blue-green ice giant.

Uranus had been seen many times before. Yet, its planetary nature was unrecognised. Britain’s first Astronomer Royal, John Flamsteed, observed Uranus six times in 1690, but catalogued it as a star.

French astronomer Pierre Charles Lemonnier observed it a dozen times between 1750 and 1769, including sightings on four consecutive nights.

For Herschel himself, as Uranus’ discoverer, the honours came thick and fast: membership to the Royal Society, receipt of the prestigious Copley Medal, a royal pension, and funding to build the biggest telescope in the world at that time.

William Herschel

Nonetheless, naming the new planet became a problem. Some astronomers felt it should be named for its discoverer. But Herschel, intent on currying favor with Britain’s King George III, suggested Georgium Sidus (“Georgian Star”).

Astronomers scoffed at the indication that the Georgian Star, in any shape or form, was a star. And to top it off, naming the world after a king was totally at odds with the classical naming tradition for planets.

The name Uranus comes from Greek mythology and was proposed in 1783 by the German astronomer Johann Elert Bode. It was a acknowledgment to the Roman god Caelus, the God of the sky and the mythological father of Saturn (Cronus), who fathered Jupiter (Zeus), who, in turn, fathered Mercury, Venus, and Mars. The name not only fit, but stuck.

Voyager 2 captured these images of Uranus at a distance of 9.1 million miles (14.5 million km) in 1986. The left image used blue, green, and orange filters, and it was processed to approximate the true color of the planet. The view on the right was taken wit different filters and the contrast was exaggerated.