URANUS ( HERSCHEL )

Uranus was the first planet to be discovered with a telescope. The third of the gas giants. Uranus was discovered in 1781 by Caroline Herschel and her brother William in 1781.William thought it was a comet at first and his calculations showed it getting bigger and bigger as he thought it approached the Earth. When observations and calculations from other astronomers in different countries came in, it was realized by them all that the Herschels had discovered a planet, and William hastily revised his data.

Some wanted to call the planet Herschel, but the Herschels called it Georgius Sidus (George's Star in Latin) after King George III who funded them. Bode suggested Uranus after the Greek God of the Heavens who had been castrated by his son Chronos the God of Time (see Saturn). Eventually this was to be accepted internationally as the planet's name.


GENDER: Masculine
USAGE: Greek Mythology (Latinized)
OTHER SCRIPTS: Ουρανος (Ancient Greek)
PRONOUNCED: yuw-RAY-nəs (English), YUWR-ən-əs (English) [key]

Meaning & History

From Greek Ουρανος (Ouranos), the name of the husband of Gaia and the father of the Titans in Greek mythology. His name is derived from ουρανος(ouranos) meaning "the heavens". This is also the name of the seventh planet in the solar system.

Uranus is the seventh planet furthest away from the Sun and it is named after the Greek god of the sky Uranus. Uranus is one of the ice giant categories of planet and it can sometimes be viewed in the night sky by the naked eye. Uranus looks like a calm, cold planet by virtue of its light blue coloring – it is certainly cold (the coldest in the solar system), but it is not calm.


The planet has had a very spectacular history. At some point in its history the planetary rotation of Uranus completely changed. Initially it will likely have rotated in a similar way to the rest of the planets in our solar system but an event occurred that made the rotation shift so that Uranus now spins on its side so rather than spinning in the same way that a spinning top would do, the planet rotates more like a ball rolling on its side.


For more fascinating facts about Uranus, read on.
The mass of Uranus is 14.5 times that of the Earth, its diameter is just 4.01 times larger than our Earth and Uranus is 2.9 billion kilometres from the Sun.

Uranus orbits the Sun once every 84.04 Earth years and completes a full rotation every 17.2 hours.

The basic composition of Uranus is similar to the other giant gas planets in our solar system with mostly hydrogen (about 80%) and helium (about 15%) present. The remainder is methane and a mixture of hydrocarbons.

The bluely green colour of Uranus is caused due to the methane in the atmosphere. This absorbs red light so the reflected sunlight is greenish blue in colour.


Uranus has a planetary ring system like Saturn but not as clear and much thinner. Currently it is understood that there are 13 rings in existence that are made up of small rocky particles.
Unusually Uranus gives off less heat than it actually absorbs from the Sun. This is because something in the history of Uranus made the planets core cool down and this means that it doesn’t radiate much heat leading to Uranus taking the prize of the coldest planet in our solar system with temperatures as low as -224 °C.

The wind speeds on Uranus can reach up to 824km / hour.Uranus has an axial tilt of 97.77 degrees. In other words it rotates on its side rather than on its axis as is the case with the other planets. There are two main theories explaining why Uranus may have such a strange rotation. The first and most accepted theory is that during the formation of the solar system an Earth sized planet smashed into Uranus permanently knocking it off its axis. The other theory is that billions of years ago another planet pulled a large moon away from Uranus and the gravitational pull caused Uranus to be knocked off its axis.


Moons of Uranus 

Uranus currently has 27 known moons. 27 satellites discovered so far. The Herschels started the custom of naming the moons of Uranus after fairies and other characters in Shakespeare's plays, with Titania and Oberon. The other larger satellites are Ariel, Umbriel, Miranda. Those discovered by Voyager 2 in 1986 have been named Cordelia, Orphelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, and Puck. Satellite discovered 2001 has been named Trinculo. Satellites discovered in 2003, have now been named Cupid and Mab.

The five main moons are called

a) Ariel,  
b) Miranda, 
c) Oberon, 
d) Titania and 
e) Umbriel.


Ariel, 579±2 kilometres radius, 1.66±0.30 density. Ariel was discovered in 1851 by William Lassell. It is still very active geologically, so few impact craters are visible. Its features are named after good spirits in world myths. Valley and fault scarps crisscross the surface, which has been smoothly flooded in places with ice. There has been tectonic activity with plate movement causing the faults on the surface. Ariel may still be an active world.


Miranda is 236±3 kilometres in radius, 1.35±0.39 density. It was discovered in 1948 by Gerard Kuiper. It has a very mixed and interesting terrain of ice, silicate rocks and frozen methane. The names of surface features are taken from Shakespeare. There are grooved landscapes, cratered like on our Moon, and also giant scarps or cliffs. There are three massive, prominent angled, ridged features. These are called the Inverness Corona, the Arden Corona and the Elsinore Corona. It is speculated that Miranda had once been severely fractured, and has since reassembled, the features being caused by the fragments. This is by no means certain though.


Oberon was also discovered by Caroline and William Herschel in 1787. Its radius is 762±4 kilometres. Its density is 1.58±0.10. Its features are named after Shakespearian heros. Oberon is mostly water ice, silicates and methane with other carbon related compounds. Its surface is heavily cratered with possible faults - there is no evidence of any recent geological activity.


Titania is 790±4 kilometres in radius, density is 1.68±0.09. Discovered by the Herschels in 1787. Its features are named after female characters in Shakespeare. Subsidence features and trenches and scarps show that Titania has has volcanic processes, perhaps caused by tidal heating, and has been an active world geologically.


Umbriel is 586±5 kilometres in radius, 1.51±0.28 density. Also discovered in 1851 by William Lassell. Its features are named after evil spirits. Umbriel is a very dark, still, world with many craters. Nothing has happened here for a very long time.
More on Cupid, Mab and the rings - dust from Mab forms one of the rings.

Rings of Uranus

Like the other gas giants, Uranus is surrounded by rings of small particles. They are very dark, and like Saturn's rings "shepherded" by tiny satellites. Nine of the rings were first discovered in 1977. (After which some astronomers wished it was not called Uranus and tried to pronounce it differently, while others enjoyed the joke). Two more rings were discovered in 1986 by Voyager 2 and more since - 12 so far.

It is possible the rings were first discovered 200 years earlier in 1727 by Herschel, (which might explain why he did not want the planet named after him).

New edge on view of the rings of Uranus from Hubble in 2007.

Orbit of Uranus

The orbit of Uranus round the Sun takes about 84 years, which is why, although it had been seen many times earlier (it is not only visible through a small telescope but to the naked eye) it had not been recognised before as another planet. The diameter of Uranus is about 52,000 kilometres. Its rotation is 17.3 hours, but as the inclination of its axis is 98 degrees, that is, it is on its side pointing down, do it looks like it rotates backwards. As it rolls along first one pole then the other pole faces the Sun.

Appearance of Uranus

Uranus looks blue in colour with not very distinct bands of cloud. On top of the clouds its temperature is 60K. There are storm clouds and vortices. Small white fluffy clouds on top of the blue bands of clouds were used to measure the speed of jet streams in the upper atmosphere which is 100 metres a second. (On Earth the jet streams are 40 metres a second). The winds are blowing in the same direction as the planet's rotation. On such a low axis this means the heat from the Sun is distributed all over the planet evenly. It does not have colder poles as on Earth.

In August 1994 Hubble took pictures of Uranus and found more interesting weather. The planet's angle to the Sun had changed as it had moved on its orbit. Unlike the other gas giants, Uranus does not have an internal heat source, so its changes in weather dependent far more on the effect of the Sun.

The poles of Uranus' magnetic field are offset from the axis of rotation by 60 degrees. This was used to calculate the rotation period of 17.3 hours. The 'magnetail' trailing behind Uranus corkscrews because of the tremendous difference between the magnetic and rotational poles.Due to Uranus having an unusual axis, this affects the seasons on the planet dramatically. For example, one of the poles on Uranus is usually pointed at the Sun so this means that although an Earth day on Uranus would only typically last 17.2 hours, if you were sat at the North Pole of Uranus a day would last 84 Earth years

Bonus fun facts

Uranus is the coldest planet in the solar system.
Uranus rotates on its side rather than every other planet that rotates (roughly) on its axis.