The God of the Sky – Uranus!

Uranus (no jokes please!) is the seventh planet from the Sun at a distance of 2.9 billion km (the Earth is at 93 million km) and is the third largest in size behind Jupiter and Saturn, although by mass it is smaller than Neptune.

The first recorded sighting of Uranus was in 1690 when it was mistakenly catalogued as a star. It wasn’t until 1781 that British astronomer William Herschel ‘discovered’ that it was something more than that and a combined effort with other scientists confirmed it was a planet. Herschel named it ‘the Georgium Sidus’ in honour of the then British king, George III.

What’s in a name?

The_Mutiliation_of_Uranus_by_Saturn‘The Georgium Sidus’ was an unpopular name and ‘Uranus’ was suggested as an alternative, in keeping with the theme of figures from classical mythology. ‘Uranus’ became the accepted name by 1850, but it is the only Greek in the sky – the rest of the planets are named after characters from Roman mythology. Uranus (taken from ‘Ouranos’) was the god of the heavens, the father of Cronus (Saturn) and the grandfather of Zeus (Jupiter). He was also god of the gods until he was overthrown by Cronus (who in turn gave way to Zeus).

Spinning sideways

Uranus has another peculiarity about it – it spins on its side. The other planets in our solar system, the Earth included, spin on an axis that is vaguely perpendicular to the ecliptic, the path of their orbit. That means that the north and south poles never point directly at the Sun. The axis of Uranus is roughly parallel to its ecliptic.


Uranus spins once every 17 hours and 14 minutes and takes about 84 Earth years to orbit the Sun. Its unusual tilt means that for a quarter of a Uranian year (roughly 21 Earth years) one pole is pointing directly at the Sun whilst the other is plunged into darkness and a very cold winter. When spring finally comes the warmth causes gigantic storms as big as North America. For years Uranus was called ‘the most boring planet’ because as Voyager 2 passed overhead it saw the height of summer with only 10 clouds to be seen. Not a very fair representation!

The Ice Giant

‘The Ice Giant’ is another of Uranus’s names as more than 80% of its mass is made up of frozen water, methane and ammonia, surrounding a rocky core. At about -183 °C on the surface, and with a minimum atmospheric temperature of -224 °C, it’s the coldest planet in the solar system. Strangely though, scientists think that there might be a huge ocean on the surface that is up to 2760 °C! Due to pressure the surface may also be littered with trillions of huge diamonds.

The thick atmosphere of Uranus is mostly hydrogen and 2% methane, which adsorbs red light, giving the planet its bluey-green appearance. Surrounding the planet are two sets of rings – the inner ones of which are black whilst the outer ones are red and blue. Uranus also has 27 moons that we know about which have been named after characters in the writings of Shakespeare and Pope (another naming oddity as all other moons are named after mythological characters).

The Magician

Gustav Holst didn’t forget Uranus: have a listen to one of the more manic movements of his Planet’s Suite: Uranus, The Magician.

The main image above is from Matt Brown, ‘The Mutilation of Uranus by Saturn’ is a painting by Giorgio Vasari, whilst the view of planetary axes is from Tfr000, all borrowed and edited with thanks under Creative Commons Licenses. The image of Uranus and its rings is in the public domain, thanks to NASA.

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