Uranus; discovered today in 1781!

238 years ago today on the 13th. March 1781, amateur astronomer William Herschel discovered a new planet: Uranus.

He was surveying the night sky when he spotted what he thought was a comet. He soon realised that it was moving too slowly for a comet. That could mean only be one thing: a planet. It took a further two years of observation to decide on just what was the nature of this object.



Uranus was the first planet to be found with a telescope. Herschel was later knighted for his historic discovery, probably helped by his trying to name it Georgium Sidus (George’s star) after his patron King George III. It took seventy years before the name Uranus was finally decided upon.

Uranus is a strange world as unlike the others it rolls around the Sun on it’s side; this is possibly the result of a collision with a very large object that knocked it over! In 1789 Herschel thought he detected a ring around the planet but it wasn’t until 1977 that rings were definitively observed from the Kuiper airborne Observatory.

PIA02963 Image from Hubble showing tilt, rings and atmospheric activity

Uranus takes 84 years to orbit the Sun and lies about 2.87 billion kilometres from the Sun. Uranus spins about its axis once every 17 hours 14 minutes, leading to a year that is 30,190 days long! A long time between birthdays. 

At magnitude 5.9, Uranus is not visible with the naked eye, but binoculars or a small telescope can reveal it as a tiny blue-green dot. It is beginning to become a real challenge to see Uranus now as the nights begin to shorten; it sets around 20:50, shortly after Venus. The easiest way to find Uranus is to locate Venus – which is the really bright object in the west at sunset. From Venus draw a line to the left and you will come to a feinter orange object, that’s the planet Mars. With your binoculars move down to the lower right of the sky and slowly sweep the area; you will make out a small object; that’s Uranus! See the map below.



Finder chart from Heavens-Above.com