The Planet Uranus

The history of physics from ancient times to the modern day, focusing on space and time. Uranus was discovered by British astronomer William Herschel in 1781. Probes first travelled past it in the 1980s. Uranus is an ice giant that moves in a different direction to the rest of the planets, so that its rings look vertical rather than horizontal.

Last updated on 5th August 2017 by Dr Helen Klus

1. Characteristics of Uranus

Uranus is the seventh closest planet to the Sun and, unlike the first six planets, it was not discovered until the invention of the telescope. Uranus was discovered by British astronomer William Herschel in 1781, who first thought it was a comet[1]. It was identified as a planet once its orbit was found to be roughly circular in 1783[2].

Uranus is the third largest planet in the Solar System, after Jupiter and Saturn. It's larger than Neptune but less massive. It takes over 30,000 days for Uranus to orbit the Sun, this is over 80 years, and one day on Uranus is just over 17 hours long[3].

Photograph of Uranus.

Uranus, image taken by the Hubble Space Telescope. Image credit: NASA, ESA, and M. Showalter/Public domain.

Unlike Mercury, Venus, Mars, Jupiter, and Saturn, Uranus was not named after a Roman god. Instead, it's named after the Ancient Greek god of the sky. Uranus is the father of the Greek god Kronos, which corresponds to the Roman god Saturn, and the grandfather of Zeus, known to the Roman's as Jupiter[4a].

Uranus is an ice giant, with an atmosphere primarily composed of hydrogen and helium, but it also contains trace amounts of hydrocarbons, and large amounts of frozen water, ammonia, and methane[4b].

Uranus has a liquid core composed mostly of water, methane, and ammonia. Uranus has a magnetosphere, but the whole planet is tilted on its side so that its magnetic poles are on the equator[4c].

Uranus has a ring system similar to Saturn's, except it didn't form when the planet did[5], and orbits at an angle of nearly 90°[6].

Planets in the Solar system, sizes are approximately to scale. Jupiter is the largest planet, followed by Saturn.

The planets, sizes approximately to scale. Image credit: Dave Jarvis/CC-SA.

2. Uranus' moons

2.1 Miranda, Ariel, Umbriel, Titania, and Oberon

Uranus has 27 moons, the five largest are Miranda, Ariel, Umbriel, Titania, and Oberon. The largest of these is Titania, which is about half the diameter of the Moon. These moons are mostly composed of frozen water and silicate rock[7].

Photographs of Uranus' moons, where the size is to scale.

Uranus' five largest moons, images from Voyager 2 (to scale). Image credit: NASA/JPL/Public domain.

3. Missions to Uranus

NASA's Voyager 2 came within 82,000 km of Uranus in 1986, travelling past its five largest moons, and discovering 10 new ones[8]. There are currently no plans for a new mission to Uranus.

Photographs of Uranus.

Uranus, image taken by Voyager 2. Image credit: NASA/Public domain.

4. References

  1. Herschel, W., 1781, 'Account of a Comet. By Mr. Herschel, FRS; Communicated by Dr. Watson, Jun. of Bath, FRS.', Philosophical Transactions of the Royal Society of London, 71, pp.492-501.

  2. Lexell, A. J., 1783, 'Recherches sur la nouvelle planète, découverte par Herschell et nommée Georgium Sidus' ('Research on the New planet discovered by Herschel and named Georgium Sidus'), Acta Academia Scientarum Imperialis Petropolitanae, 1, pp.303–329.

  3. NASA, 'Planetary Fact Sheet', last accessed 01-06-17.

  4. (a, b, c) NASA, 'Uranus: In Depth', last accessed 01-06-17.

  5. NASA, 'Rings of Uranus', last accessed 01-06-17.

  6. NASA, 'Hubble Camera Snags Rare View of Uranus Rings', last accessed 01-06-17.

  7. NASA, 'Uranus: Moons', last accessed 01-06-17.

  8. NASA, 'Uranus', last accessed 01-06-17.

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The Star Garden is a science news and science education website run by Dr Helen Klus.

How we came to know the cosmos covers the history of physics focusing on space and time, light and matter, and the mind. It explains the simple discoveries we made in prehistoric times, and how we built on them, little by little, until the conclusions of modern theories seem inevitable. This is shown in a timeline of the universe.

The Star Garden covers the basics for KS3, KS4, and KS5 science revision including SATs, GCSE science, and A-level physics.

Space & Time

Pre 20th Century theories

1. History of Constellations

2. History of Latitude

3. History of Longitude

4. Models of the Universe

5. Force and Energy

6. Newton's theory of Gravity

7. Age of the Universe

20th Century discoveries

1. Special Relativity

2. General Relativity

3. Big Bang theory

4. History of Galaxies

5. Life Cycles of Stars

6. Red Giants and White Dwarfs

7. Neutron Stars and Black Holes

Missions to planets

1. The planet Mercury

2. The planet Venus

3. The planet Earth

3.1 The Earth's Moon

4. The planet Mars

4.1 The Asteroid Belt

5. The planet Jupiter

6. The planet Saturn

7. The planet Uranus

8. The planet Neptune

Beyond the planets

1. Kuiper Belt and Oort Cloud

2. Pioneer and Voyager

3. Discoveries of Exoplanets