Uranus is a gas giant planet that is often referred to as an ice giant and in terms of composition and size it has a lot more in common with its neighbour Neptune than it does with the gas giant planets Jupiter and Saturn.

Uranus is the seventh planet from the Sun and it is not generally visible to the naked eye. You would need to use a well powered telescope to be able to view Uranus in the night sky with certainty. In fact it was the first planet that was discovered by the use of a telescope.

The planet Uranus is unusual because it tilts at around 98 degrees, so the equator is nearly at right angles to its orbit – this is the only planet in our solar system to tilt this dramatically.

Photo of Uranus taken by the Hubble Space Telescope Uranus taken by the Keck Telescope Near-infrared picture of Uranus with 2 of its moons - Miranda and Ariel, Subaru Telescope, Japan
Click an image above to view full size image. Hover over for description.

What's in a name?

Uranus as it is now known may well have been observed in ancient times but due to the lack of magnifying equipment at the time it was likely recorded incorrectly.

It is thought that the Greek astronomer was the first to observe Uranus in around 128BC, but noted the object as a star. John Flamsteed later made several definite sightings in 1690 which he recorded as 34 Tauri. It was only until 1781 when Sir William Herschel viewed Uranus that it was officially recorded as a planet and named accordingly. Even then, Herschel was convinced initially that it was a comet he was observing.

Uranus is the only planet in our solar system that does not have a name associated to a Roman god. As Herschel officially discovered the planet he was given the right to name the planet. He originally wanted to call the planet Georgium Sidus (or George’s Star) after the then monarch King George III, but this name was not popular outside of Britain. Johann Elert Bode suggested the name Uranus, which is the Latinised version of the Greek god of the sky, Ouranos.

The argument followed that because in mythology Saturn was the father of Jupiter, it should follow that the new planet should be named after the father of Saturn. Therefore, the name Uranus was adopted and it is the only planet that is derived from Greek mythology rather than Roman mythology.

Uranus Facts

Uranus is the seventh planet from the Sun and has an average distance from the Sun of 2.88 billion kilometres.

Uranus has a diameter of just over 4 times the size of the Earth and it has a mass that is nearly 15 times greater than that of the Earth.

Uranus completes a full rotation once every 17 hours which means a day on Uranus only lasts for 17 Earth hours. For Uranus to complete a full orbit around the Sun (a year on Uranus) it would take 84 Earth years.

Uranus is known to have 27 moons at this time. Interestingly, they are all named after literary characters in classic English literature (works from Shakespeare and Pope). The main moons are called Ariel, Miranda, Oberon, Titania and Umbriel.

It is believed that Uranus has the coldest planetary atmosphere at an average of -224 degrees Celsius.

The planet has a complex cloud structure that is composed of water based clouds at a lower level, and at the higher level a methane based cloud structure. It is the methane that gives Uranus the pleasant bluish colouration.

The surface of Uranus is made up largely of rock and ice.
Uranus does have a ring structure but it is faint in comparison to Saturn. It is believed to have 13 major rings that are made up of small rocky fragments.

The wind speeds on Uranus can reach nearly 900km/h.

Uranus has a permanent tilt of approximately 98 degrees. It is believed that this was not the original planetary rotation. There are two theories as to why Uranus spins on its side instead of on its axis. The first theory is that a large collision with an Earth sized planet in the early formation of the solar system knocked Uranus permanently off its axis. The second theory is that early in the life of the solar system another planet pulled a moon away from Uranus and it was this gravitational pull that knocked Uranus off its axis.

Uranus has had little close hand investigation. Only one craft has conducted a flyby of Uranus. NASA’s Voyager 2 flew past Uranus in 1986 and this is the only spacecraft to have done so. There are no other spacecraft missions to Uranus taking place at this time.

Figures and Statistics

  Uranus Earth Ratio (Planet to Earth)
Rotation period - (hours) 17.24 23.9345 0.720
Length of day - (hours) 17.24 24.00 0.718
Length of year (earth days) 369.66 365 1.013
One complete orbit takes (earth days) 30799.095 365.256 84.322
Radius (km) 25559 6378.1 4.007
Mass (1024 kg) 86.816 5.9726 14.536
Volume (1013 km3) 6.833 108.321 63.086
Density (kg/m3) 1271 5514 0.231
Distance from Earth - Min (106km) 2581.9 - -
Distance from Earth - Max - (106km) 3157.3 - -
Average distance from Sun (106km) 2,872.46 149.6 19.201
Orbital radius (109km) 2.741-3.004 0.147-0.152 18.64-19.76
Orbital velocity (average - km/s) 6.81 29.78 0.229
Rotational velocity (km/h) 9320 1674.4 5.566
Surface gravity (m/s2) 8.87 9.81 0.904
Surface temp - Min (K) 53 184 0.288
Surface temp - Max (K) 76 330 0.230
Axial tilt (degrees) 97.77 23.44 4.171
Number of natural satellites (moons) 27 1 27