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|Discovered by||William Herschel|
|Discovered on||March 13, 1781|
|Orbital characteristics (Epoch J2000)|
|Semi-major axis|| 2,870,972,220 km|
19.191 263 93 AU
|Orbital circumference|| 18.029 Tm|
|Eccentricity||0.047 167 71|
|Perihelion|| 2,735,555,035 km|
18.286 055 96 AU
|Aphelion|| 3,006,389,405 km|
20.096 471 90 AU
|Orbital period|| 30,708.1600 d|
|Synodic period||369.65 d|
|Orbital speed||6.795 km/s|
|Max. Orbital Speed||7.128 km/s|
|Min. Orbital Speed||6.485 km/s|
|Inclination|| 0.769 86°|
(6.48? to Sun's equator)
| Longitude of the|
| Argument of the|
|Number of satellites||27|
|Equatorial diameter|| 51,118 km|
|Polar diameter|| 49,946 km|
|Surface area|| 8.084×109 km2|
|Volume|| 6.834×1013 km3|
|Mass|| 8.6832×1025 kg|
|Mean density||1.318 g/cm3|
|Equatorial gravity|| 8.69 m/s2|
|Escape velocity||21.29 km/s|
|Rotation period||−0.718 333 333 d (17 h 14 min 24.000 00 s) 1 (http://www.hnsky.org/iau-iag.htm)|
|Rotation velocity||2.59 km/s = 9320 km/h (at the equator)|
| Right ascension|
of North pole
|77.31° (5 h 9 min 15 s)|
|Cloudtop avg. temp.||55 K|
|Atmospheric pressure||120 kPa|
| Carbon monoxide|
Uranus (pronounced "yər-AYN-us", or "YOOR-ə-nus") is the seventh planet from the Sun. It is a gas giant, the third largest by diameter and fourth largest by mass. It was named after the Greek god Ouranos, and is the only planet in the solar system named after a Greek god: all others are named after Roman deities. Its symbol is either ♅ (Unicode U+2645, mostly astrological) or Missing image
Astronomical symbol for Uranus
Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a little helium (in contrast to Jupiter and Saturn which are mostly hydrogen). Uranus (like Neptune) is in many ways similar to the cores of Jupiter and Saturn minus the massive liquid metallic hydrogen envelope. It appears that Uranus does not have a rocky core like Jupiter and Saturn but rather that its material is more or less uniformly distributed. Uranus' cyan color is due to the absorption of red light by atmospheric methane.
One of the most distinctive features of Uranus is its axial tilt of almost ninety degrees. Consequently, for part of its orbit one pole faces the Sun continually whilst the other pole faces away. At the other side of Uranus' orbit the orientation of the poles towards the Sun is reversed. Between these two extremes of its orbit the Sun rises and sets around the equator normally.
At the time of Voyager 2's passage in 1986, Uranus' south pole was pointed almost directly at the Sun. Note that the labelling of this pole as "south" is actually in some dispute. Uranus can either be described as having an axial tilt of slightly more than 90°, or it can be described as having an axial tilt of slightly less than 90° and rotating in a retrograde direction; these two descriptions are exactly equivalent as physical descriptions of the planet but result in different definitions of which pole is the North Pole and which is the South Pole.
One result of this odd orientation is that the polar regions of Uranus receive a greater energy input from the Sun than its equatorial regions. Uranus is nevertheless hotter at its equator than at its poles, although the underlying mechanism which causes this is unknown. The reason for Uranus' extreme axial tilt is also not known. It is speculated that perhaps during the formation of the planet it collided with an enormous protoplanet, resulting in the skewed orientation.
It appears that Uranus' extreme axial tilt also results in extreme seasonal variations in its weather. During the Voyager 2 flyby, Uranus' banded cloud patterns were extremely bland and faint. Recent Hubble Space Telescope observations, however, show a more strongly banded appearance now that the Sun is approaching Uranus' equator. By 2007 the Sun will be directly over Uranus' equator.
Uranus' magnetic field is odd in that it is not centered on the center of the planet and is tilted almost 60° with respect to the axis of rotation. It is probably generated by motion at relatively shallow depths within Uranus. Neptune has a similarly displaced magnetic field, suggesting that this is not necessarily a result of Uranus' axial tilt. The magnetotail is twisted by the planet's rotation into a long corkscrew shape behind the planet. The magnetic field's source is unknown; the electrically conductive, super-pressurized ocean of water and ammonia once thought to lie between the core and the atmosphere now appears to be nonexistent.
Discovery and naming of Uranus
Uranus was the first planet to be discovered that was not known in ancient times, although it had been observed on many previous occasions but was always dismissed as simply another star. The earliest recorded sighting was in 1690 when John Flamsteed catalogued it as 34 Tauri. Flamsteed observed Uranus twice again, in 1712 and 1715. Bradley observed it in 1748, 1750 and 1753; Mayer in 1756. Lemonnier observed it four times in 1750, twice in 1768, six times in 1769, and one last time in 1771. He was a victim of his own disorderliness: one of his observations was found consigned on a paper bag used to store hair powder!
Sir William Herschel discovered the planet on March 13, 1781, but reported it on April 26, 1781 as a "comet": Account of a Comet, By Mr. Herschel, F. R. S.; Communicated by Dr. Watson, Jun. of Bath, F. R. S., Philosophical Transactions of the Royal Society of London, Volume 71, pp. 492-501.
Herschel originally named it Georgium Sidus (George's Star) in honour of King George III of England. When it was pointed out that sidus means star and not planet, he rebaptised it the Georgian Planet. In any case, this name was not acceptable outside of Britain. Lalande proposed in 1784 to name it Herschel, at the same time that he created the planet's symbol ("a globe surmounted by your initial"); his proposal was readily adopted by French astronomers. Prosperin, of Uppsala, proposed the names Astraea, Cybele, and Neptune (now borne by two asteroids and a planet). Lexell, of St. Petersburg, compromised with George III's Neptune and Great-Britain's Neptune. Bernoulli, from Berlin, suggested Hypercronius and Transaturnis. Lichtenberg, from G?ngen, chimed in with Austr䡧', a goddess mentioned by Ovid (but who is traditionally associated with Virgo). The name Minerva was also proposed  (http://vesuvius.jsc.nasa.gov/er/seh/hersc.html). Finally, Bode, as editor of the Berliner Astronomisches Jahrbuch, opted for Uranus, after the Greek god; Hell followed suit by using it in the first ephemeris, published in Vienna. Examination of earliest issues of Monthly Notices of the Royal Astronomical Society from 1827 shows that the name Uranus was already the most common name used even by British astronomers by then, and probably earlier. The name Georgium Sidus or "the Georgian" were still used infrequently (by the British alone) thereafter. The final holdout was HM Nautical Almanac Office, which did not switch to Uranus until 1850.
Exploration of Uranus
The brightness of Uranus is between magnitude +5.5 and +6.0, so it can be seen with the naked eye as a faint star under dark sky conditions. It can be easily found with binoculars. From Earth it has a diameter of 4". Even in large telescopes no details can be seen on its disc.
|Stationary, retrorad||Opposition||Stationary, prograd||Conjunction to sun|
|June 10th, 2004||August 27th, 2004||November 12th, 2004||February 22nd, 2004|
|June 15th, 2005||September 1st, 2005||November 16th, 2005||February 25th, 2005|
|June 19th, 2006||September 5th, 2006||November 20th, 2006||March 1st, 2006|
|June 23rd, 2007||September 9th, 2007||November 24th, 2007||March 5th, 2007|
|June 27th, 2008||September 13th, 2008||November 27th, 2008||March 8th, 2008|
|Jule 1st, 2009||September 17th, 2009||December 2nd, 2009||March 13th, 2009|
|Jule 6th, 2010||September 21st, 2010||December 6th, 2010||March 17th, 2010|
The rings of Uranus
Main article: Rings of Uranus
Uranus has a faint planetary ring system, composed of dark particulate matter up to 10 metres in diameter. This ring system was discovered in March 1977 by James L. Elliot, Edward W. Dunham, and Douglas J. Mink, using the Kuiper Airborne Observatory. The discovery was serendipitous; they planned to use the occultation of a star by Uranus to study the planet's atmosphere, but when they analysed their observations they found that the star had disappeared briefly from view five times both before and after it disappeared behind the planet. They concluded that there must be a ring system around the planet; it was directly detected when the Voyager 2 space probe passed Uranus in 1986.
The moons of Uranus
Main article: Uranus' natural satellites
For a timeline of discovery dates, see Timeline of natural satellites.
Uranus has 21 named moons. List of named moons:
Uranus in fiction
- In the animated series Futurama, in 2620 the name of Uranus was changed to Urectum to get rid of "That Stupid Joke" once and for all.
Uranus in astrology
Main article: Planets in astrology#Uranus
- NASA's Uranus fact sheet (http://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html)
- Keck pictures of Uranus show best view from the ground (http://www2.keck.hawaii.edu/news/science/uranus/) -- Press release with some photographs showing rings, satellites and clouds
Clipart and Pictures
- Pictures of Earth (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Earth)
- Pictures of Jupiter (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Jupiter)
- Pictures of Mars (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Mars)
- Pictures of Mercury (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Mercury)
- Pictures of Neptune (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Neptune)
- Pictures of Pluto (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Pluto)
- Pictures of Saturn (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Saturn)
- Pictures of Uranus (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Uranus)
- Pictures of Venus (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Planets/Venus)
- Pictures of Galaxies and Stars (http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Space/Galaxies_and_Stars)
Lesson Plans and Activities
- Solor System Lesson Plans (http://lessonplancentral.com/lessons/Space/Solar_System/index.htm)
| Uranus' natural satellites |
|Cordelia | Ophelia | Bianca | Cressida | Desdemona | Juliet | Portia | Rosalind | S/2003 U 2 | Belinda|
|S/1986 U 10 | Puck | S/2003 U 1 | Miranda | Ariel | Umbriel | Titania | Oberon | S/2001 U 3|
|Caliban | Stephano | Trinculo | Sycorax | S/2003 U 3 | Prospero | Setebos | S/2001 U 2|