Shagbark looks at Uranus
Created | Updated Mar 26, 2011
Uranus is the seventh planet from our sun and is a gas giant.
Its blue-green colour is caused by methane gas in an atmosphere mainly composed of hydrogen and helium. Here is a picture of the planet with its rings
Source: Hubblesite.org.
The Facts
- Mass (kg): 86.832x1024
- Equatorial Radius (km): 25,559
- Mean Density (kg/m3): 1250
- Length of Day (hours): 17.24
- Orbital Period (earth years): 84.016846
- Acceleration due to Gravity (m/s2): 8.69
- Mean Orbital Velocity (km/s): 6.81
- Inclination of Axis : 97.77 °
- Mean Distance from the Sun : 19.19 AU
The Discovery of Uranus
William Herschel discovered Uranus on March 13, 1781. He called it Georgium Sidus, meaning 'star of George', after George III, his patron. After that it was known as Herschel in his honour, before Johann Elert Bode suggested the name Uranus, after the Greek god of the heavens, husband of Gaea and father of the Titans.
The Planet
A gas giant located between Saturn and Neptune, this planet has drawn little attention to itself. Astronomers noted its tilt but could see few details on its face.
However by the middle of
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advances in adaptive optics1 began to give a better picture of what Uranus is like.
Uranus seems to have been pushed over on to its side. Its axial tilt is 97.77°, which means that it rotates on its side. This means that at the poles, days last for 42 Earth years, half of the Uranian year. It also affects the seasons. When Voyager 2 flew by it was the height of austral summer this meant that the northern hemisphere was in frigid darkness facing away from the sun. As the equinox in 2007 approaches the Northern hemisphere is becoming more active. Uranus looks very bland, but actually has fast-moving clouds in its upper atmosphere, which are very faint. It's atmosphere is subject to seasonal variations; different things happen as the Sun is in different parts of the Uranian sky
Uranus, like Neptune, is mainly made up of rocks and ice beneath its atmosphere, but unlike Jupiter and Saturn, it doesn't have large amounts of liquid hydrogen2. The core of Uranus is relatively small and is wrapped in a mantle of pressurized slush composed of ammonia, water and methane. This creates a powerful magnetic field. As the magnetic pole is tilted some sixty degrees to the axis it turns the planet's magnetosphere like a corkscrew.
The Rings and Satellites
In 1977 James L Eliot,an American astronomer,
first observed the planet's rings. He was observing the planet passing before a star - an event called an occultation - when he saw them. They are named Alpha, Beta, Gamma, Delta and Epsilon, starting at the inner ring, and Voyager 2 found a further four rings. And in 2005 two more were verified. The rings are quite dark, like those of Jupiter, with the brightest being the Epsilon ring. It has been suggested that they are only one particle thick which would make them invisible if seen edge on.
Astronomers continue to find moons around Uranus. As of 2006 twenty-seven had been sighted. They are listed here in order of discovery with the size in km and year first sighted.
| Name... | size(km) | Year | |
| Oberon | 1522 | 1787 | |
| Titania | 1578 | 1787 | |
| Umbriel | 1169 | 1851 | |
| Ariel | 1158 | 1851 | |
| Miranda | 471 | 1948 | |
| Puck | 162 | 1985 | |
| Cordelia | 40 | 1986 | |
| Ophelia | 42 | 1986 | |
| Bianca | 51 | 1986 | |
| Desdemona | 64 | 1986 | |
| Rosalind | 72 | 1986 | |
| Belinda | 80 | 1986 | |
| Cresida | 80 | 1986 | |
| Juliet | 93 | 1986 | |
| Portia | 135 | 1986 | |
| Caliban | 72 | 1997 | |
| Sycorax | 150 | 1997 | |
| Perdita | 20 | 1999 | |
| Stepheno | 32 | 1999 | |
| Setebos | 47 | 1999 | |
| Prospero | 50 | 1999 | |
| Franscisco | 22 | 2001 | |
| Trinculo | 18 | 2001 | |
| Margaret | 20 | 2003 | |
| Ferdinand | 21 | 2003 | |
| Cupid | 10 | 2003 | |
| Mab | 10 | 2003 |
At one point, astronomers 'lost' two of Uranus's satellites, Cordelia and Ophelia. They shepherd the Epsilon ring, and were discovered by Voyager 2. They are both very small, and were being tracked prior to observations by the Hubble Space telescope, when they were lost, although happily they have been found again now.
The h2g2 Tour of the Solar System
Take the h2g2 Shuttle for your whistle-stop tour of the Solar System.
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