Uranus
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 Uranus, as seen by Voyager 2 |
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| Discovery | ||||||||||
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| Discovered by: | William Herschel | |||||||||
| Discovery date: | March 13, 1781 | |||||||||
| Orbital characteristics | ||||||||||
| Epoch J2000 | ||||||||||
| Aphelion distance: | 3,006,389,405 km 20.096 471 90 AU 1,868,088,249 miles |
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| Perihelion distance: | 2,735,555,035 km 18.286 055 96 AU 1,699,799,169 miles |
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| Semi-major axis: | 2,870,972,220 km 19.191 263 93 AU 1,783,943,710 miles |
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| Orbital circumference: | 18.029 Tm 120.515 AU |
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| Eccentricity: | 0.047 167 71 | |||||||||
| Sidereal period: | 30,707.4896 day (84.07 yr) |
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| Synodic period: | 369.65 day | |||||||||
| Avg. orbital speed: | 6.795 km/s | |||||||||
| Max. orbital speed: | 7.128 km/s | |||||||||
| Min. orbital speed: | 6.486 km/s | |||||||||
| Inclination: | 0.769 86° (6.48° to Sun's equator) |
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| Longitude of ascending node: | 74.229 88° | |||||||||
| Argument of perihelion: | 96.734 36° | |||||||||
| Satellites: | 27 | |||||||||
| Physical characteristics | ||||||||||
| Equatorial radius: | 25,559 km (4.007 Earths) |
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| Polar radius: | 24,973 km (3.929 Earths) |
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| Oblateness: | 0.0229 | |||||||||
| Surface area: | 8.084×109 km2 (15.849 Earths) |
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| Volume: | 6.834×1013 km3 (63.086 Earths) |
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| Mass: | 8.6832×1025 kg (14.536 Earths) |
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| Mean density: | 1.318 g/cm3 | |||||||||
| Equatorial surface gravity: | 8.69 m/s2 (0.886 g) |
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| Escape velocity: | 21.29 km/s | |||||||||
| Sidereal rotation period: | −0.718 33 day (17 h 14 min 24 s by convention) [1] | |||||||||
| Rotation velocity at equator: | 2.59 km/s = 9320 km/h | |||||||||
| Axial tilt: | 97.77° | |||||||||
| Right ascension of North pole: | 77.31° (5 h 9 min 15 s) | |||||||||
| Declination of North pole: | +15.175° | |||||||||
| Albedo: | 0.51 | |||||||||
| Surface temp.: Surface Cloudtop |
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| Adjectives: | Uranian | |||||||||
| Atmosphere | ||||||||||
| Surface pressure: | 120 kPa (at the cloud level) | |||||||||
| Composition: | 83% Hydrogen 15% Helium 1.99% Methane 0.01% Ammonia 0.00025% Ethane 0.00001% Acetylene trace Carbon monoxide trace Hydrogen sulfide |
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Uranus (IPA: [ jʊˈɹeɪ.nəs, ˈjʊ.ɹə.nəs ], named after the Greek god of the sky (Uranus , Οὐρανός), is the seventh planet from the Sun. It is a gas giant, the third largest by diameter and fourth largest by mass. Its symbol is either 
(astrological) or 
(astronomical). The first symbol derives from the name of its discoverer, William Herschel. The second symbol is a combination of the devices for the Sun and Mars, as Uranus was the personification of heaven in Greek mythology, dominated by the light of the Sun and the power of Mars. It is also the alchemical symbol of platinum.
Uranus is the first planet discovered in modern times. Sir William Herschel formally discovered the planet on March 13, 1781; the other planets (from Mercury out to Saturn) have been known since ancient times, since they are visible to the naked eye. Uranus' discovery expanded the boundaries of the solar system for the first time in modern human history. It was also the first planet discovered using technology (a telescope) rather than the naked eye.
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Discovery and naming
Uranus is the first planet to be discovered that was not known in ancient times; although it had been observed on many previous occasions, it was often mistakenly identified as a star. The earliest recorded sighting was in 1690 when John Flamsteed catalogued Uranus as 34 Tauri. Flamsteed observed Uranus at least six more times. The record belongs to a French astronomer, Pierre Lemonnier, who observed Uranus at least twelve times between 1750 and 1771, including on four consecutive nights. (Lemonnier is often[citation needed] called careless or even "sloppy" for this, but it is important to know that he realized 9 of these within a short time of Herschel's discovery and most of his observations occurred at the stationary point in Uranus' orbit.)
Sir William Herschel discovered the planet on March 13, 1781, but reported it on April 26, 1781, as a "comet."[2]
On the 13th of March, 1781, between ten and eleven o'clock at night, while Herschel was examining the small stars near H Geminorum with a seven-foot telescope, bearing a magnifying power of two hundred and twenty-seven times, one of these stars seemed to have an unusual diameter; and it was, therefore, thought to be a comet. It was under this denomination that it was discussed at the Royal Society of London. But the researches of Herschel and of Laplace showed later that the orbit of the new body was nearly circular, and Uranus was consequently elevated to the rank of a planet. [3] Herschel originally named it Georgium Sidus (George's Star) in honour of King George III of Great Britain (c.f. American poet Elizabeth Graeme Fergusson's "Upon the Discovery of the Planet..." about the event). When it was pointed out that sidus means star and not planet, Herschel rebaptised it the Georgian Planet. 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 (astrological) 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 another 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 Göttingen, chimed in with Austräa, a goddess mentioned by Ovid (but who is traditionally associated with Virgo). The name Minerva was also proposed.[4] Finally, Bode, as editor of the Berliner Astronomisches Jahrbuch, opted for Uranus,[5] after Latinized version of the Greek god of the sky, Ouranos; Maximilian Hell followed suit by using it in the first ephemeris, published in Vienna and computed by the Benedictine priest Placidus Fixlmillner. The earliest publication to include Uranus in its title was in 1823.[6][7] The name was in use in Germany at least as far back as 1791, however.[8] 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" was still used infrequently (by the British alone) thereafter. The final holdout was HM Nautical Almanac Office, which did not switch to Uranus until 1850.[5]
The stressed syllable in the name is properly the first, antepenultimate syllable, since in Latin the penultimate vowel a is short (ūrănŭs) and in an open syllable, and such syllables are never stressed in Latin. The historically correct pronunciation of the name by English-speakers is therefore [ ˈjʊ.rə.nəs ]. The historically incorrect pronunciation [ jʊˈɹeɪ.nəs ], with stress on the second syllable and a "long a" (ūrānŭs) have become very common, however, perhaps through the influence of the related adjective "Uranian" (always pronounced [ jʊˈɹeɪ.ni.ən ] or the similarly-pronounced name of the element uranium.
In the Chinese, Japanese, Korean, and Vietnamese languages, the planet's name is literally translated as the sky king star (天王星)[9][10], while in India it is named Aruna (Devanāgarī अरुण), the charioteer of the sun god Surya in Hindu mythology.
Physical characteristics
Composition
Uranus is composed primarily of gas and various ices. The atmosphere is about 83 percent hydrogen, 15 percent helium, 2 percent methane and traces of acetylene. The interior is richer in heavier elements, most likely compounds of oxygen, carbon, and nitrogen, as well as rocky materials. This is in contrast to Jupiter and Saturn which are mostly hydrogen and helium. Uranus (like Neptune) is very much similar to the cores of Jupiter and Saturn without the massive fluid metallic hydrogen envelope. Uranus' cyan color is due to the absorption of red light by atmospheric methane. Surface temperature on Uranus' cloud cover is approximately 55 K (−218 °C or −360 °F).[11]
Axial tilt
One of the most distinctive features of Uranus is its axial tilt of ninety-eight degrees. Consequently, for part of its orbit one pole faces the Sun continually while the other pole faces away. At the other side of Uranus's orbit the orientation of the poles towards the Sun is reversed. This gives each pole 42 years of continuous sunlight, followed by 42 years of darkness. Between these two extremes of its orbit, particularly at the equinoxes, the Sun rises and sets around the equator normally. Uranus will reach its next equinox around December 2007, and not again until 2049.[12]
| Season, Northern Hemisphere | Year | Season, Southern Hemisphere |
|---|---|---|
| Winter Solstice | 1902, 1986 | Summer Solstice |
| Vernal Equinox | 1923, 2007 | Autumnal Equinox |
| Summer Solstice | 1944, 2028 | Winter Solstice |
| Autumnal Equinox | 1965, 2049 | Vernal Equinox |
At the time of Voyager 2's passage in 1986, Uranus' south pole was pointed almost directly at the Sun. The labelling of this pole as "south" uses the coordinate definitions currently endorsed by the International Astronomical Union, namely that the north pole of a planet or satellite shall be the pole which points above the invariable plane of the solar system (regardless of the direction the planet is spinning) [1] [2]. A different system is sometimes used, defining a body's north and south poles according to the right-hand rule in relation to the direction of rotation [3]. In terms of this latter coordinate system it was Uranus' north pole which was in sunlight in 1986. On page 47 of the September 2006 issue of the Sky at Night magazine, Patrick Moore, commenting on the issue, sums up "take your pick!"
One result of this 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[citation needed] that during the formation of the Solar System, an Earth sized protoplanet collided with Uranus, causing 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's overhead position relative to Uranus is approaching Uranus' equator. By 2007 the Sun will be directly over Uranus' equator.
Magnetic field
Uranus's magnetic field is peculiar since it is not originating from the geometric center of the planet and is tilted almost 60° from the axis of rotation. It is probably generated by motion at relatively shallow depths within Uranus. Neptune has a similarly displaced magnetic field, which suggests the magnetic field is not necessarily a consequence 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.
Explanation for bland atmosphere
The internal heat of Uranus is lower than that of Jupiter and Saturn. Both Jupiter and Saturn radiate more energy than they receive from the Sun. This causes many powerful convection currents to form in the atmosphere. On Uranus that heat source is much lower due to its lower mass, with the temperature of its core roughly 7000 K compared to 30 000 K at Jupiter's core and 18 000 K at Saturn. The convection currents formed in the Uranian atmosphere are not as strong and hence it lacks the atmosphere banding of the larger gas giants. However, as stated above, the weather patterns of Uranus do vary with season, being more pronounced at the equinoxes than at the solstices.
Cloud features
For a short period in Autumn 2004, a number of large clouds appeared in the Uranian atmosphere, giving it a Neptune-like appearance. [13] On August 23, 2006, researchers at the Space Science Institute (Boulder, CO) and the University of Wisconsin observed a dark spot on Uranus' surface, giving astronomers more insight into the planet's atmospheric activity.[14]
Planetary rings
Uranus has a faint planetary ring system, composed of dark particulate matter up to ten meters in diameter. This ring system was discovered March 10, 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 the star SAO 158687 by Uranus to study the planet's atmosphere. However, when their observations were analyzed, 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 imaged when Voyager 2 passed Uranus in 1986.
In December 2005, the Hubble Space Telescope detected a pair of previously unknown rings. The largest is located at twice the distance from the planet than the previously known rings. The new rings are so far from the planet that they are being called Uranus' "outer" ring system. Hubble also spotted two small satellites. One, Mab, shares its orbit with the outermost newly discovered ring. These two rings bring the total number of Uranus rings to 13.
In April 2006, images of the new rings with the Keck Observatory yielded the colors of the outer rings: one was blue and the other red. [15] A marked similarity to the colorful E and G rings of Saturn may be a coincidence, or it may be related to a similar causal mechanism. The source of the rings' colors are still an area of active research. The planet's inner rings appear grey.
Exploration
NASA's Voyager 2 is the only spacecraft to have visited the planet and no other visits are currently planned. Launched in 1977, Voyager 2 made its closest approach to Uranus on January 24, 1986, before continuing its journey to Neptune.
Natural satellites
Uranus has 27 known natural satellites. The names for these satellites are chosen from characters from the works of Shakespeare and Alexander Pope. The five main satellites are Miranda, Ariel, Umbriel, Titania and Oberon.
The Uranian satellite system is the least massive among the gas giants; indeed, the combined mass of the five major satellites would be less than half that of Triton alone. The moons are low-albedo, ice-rock conglomerates.[16]
| Name |
Diameter (km) |
Mass (kg) |
Orbital radius (km) |
Orbital period (d) |
|
|---|---|---|---|---|---|
| Miranda | IPA: [ mɪˈɹæn.də ] | 470 (14%) |
7.0×1019 (0.1%) |
129,000 (35%) |
1.4 (5%) |
| Ariel | IPA: [ ˈe.ɹiˌɛl ] | 1160 (33%) |
14×1020 (1.8%) |
191,000 (50%) |
2.5 (10%) |
| Umbriel | IPA: [ ˈʌm.bɹiˌɛl ] | 1170 (34%) |
12×1020 (1.6%) |
266,000 (70%) |
4.1 (15%) |
| Titania | IPA: [ tɪˈteɪ.ni.ə ]] or [ taɪˈteɪ.ni.ə ] |
1580 (45%) |
35×1020 (4.8%) |
436,000 (115%) |
8.7 (30%) |
| Oberon | IPA: [ˈoʊ.bə.ɹɑn ] | 1520 (44%) |
30×1020 (4.1%) |
584,000 (150%) |
13.5 (50%) |
Visibility
- Further information: Aspects of Uranus
The brightness of Uranus is between magnitude +5.5 and +6.0. Thus, under dark sky conditions it can be seen with the naked eye as a faint star. From Earth, it has a diameter of four arcseconds. It is an easy target with binoculars. In larger amateur telescopes with an objective diameter greater than 12" (30 cm), the planet appears as a pale blue disk with distinct limb darkening. The larger satellites, Titania and Oberon, may be visible. Because of its faintness and slow apparent motion, it was never recognised as a planet by ancient astronomers.
As the planet approaches its 2007 equinox, dynamic cloud activity is developing. Most of the activity requires Hubble Space Telescope or large telescopes with adaptive optics to be detectable. However, some features may become bright enough to be seen with moderately large amateur telescopes. In 2006, a Dark Spot was detected in visible-wavelength Hubble images, suggesting that the atmosphere of Uranus near equinox is becoming more like that of Neptune. [17]
See also
References
- ^ REPORT OF THE IAU/IAG WORKING GROUP ON CARTOGRAPHIC COORDINATES AND ROTATIONAL ELEMENTS OF THE PLANETS AND SATELLITES: 2000.
- ^ 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.
- ^ M. Arago (1871), Herschel, Annual Report of the Board of Regents of the Smithsonian Institution, pp. 198-223
- ^ (1986) "Voyager at Uranus". NASA JPL 7 (85): 400-268.
- ^ a b Littmann, Mark (2004). Planets Beyond: Discovering the Outer Solar System. Courier Dover Publications, pp. 10-11. ISBN 0-486-43602-0.
- ^ NASA's ADS
- ^ Schwerd, Friedrich Magnus. "Opposition des Uranus 1821". Astronomische Nachrichten 1: 18-21.
- ^ Fixlmillner, Placido (1791). Acta Astronomica Cremifanensia. Steyr, AT: Franz Josef Medter.
- ^ Sailormoon Terms and Information. The Sailor Senshi Page. Retrieved on March 5, 2006.
- ^ (October 1997) "Asian Astronomy 101". Hamilton Amateur Astronomers 4 (11).
- ^ Lunine J. I. (1993). "The Atmospheres of Uranus and Neptune". Annual Review of Astronomy and Astrophysics 31: 217-263. DOI:10.1146/annurev.aa.31.090193.001245.
- ^ http://www.sciencedaily.com/releases/2006/10/061001211630.htm
- ^ Keck zooms in on the weird weather of Uranus. University of Wisconsin-Madison Website. Retrieved on December 24, 2006.
- ^ http://www.seti.org/site/apps/nl/content2.asp?c=ktJ2J9MMIsE&b=194993&ct=3198251
- ^ UC Berkeley News (2006-04-06). Blue ring discovered around Uranus. Press release. Retrieved on 2006-10-03.
- ^ "Voyager Uranus Science Summary", http://www.solarviews.com/eng/vgrur.htm (Accessed 1/28/07).
- ^ New Images Reveal Clouds on Planet Uranus. Space.com (2004). Retrieved on March 5, 2006.
External links
| Find more information on Uranus by searching Wikipedia's sister projects | |
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Dictionary definitions from Wiktionary |
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Textbooks from Wikibooks |
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Quotations from Wikiquote |
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Source texts from Wikisource |
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Images and media from Commons |
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News stories from Wikinews |
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Learning resources from Wikiversity |
- NASA's Uranus fact sheet
- Keck pictures of Uranus show best view from the ground - Press release with some photographs showing rings, satellites and clouds
- News reports of 22 December 2005 rings and moons discovery
- Planets - Uranus A kid's guide to Uranus.
- Uranus at Jet Propulsion Laboratory's planetary photojournal.
- Spring Has Sprung on Uranus
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| Inner | Cordelia · Ophelia · Bianca · Cressida · Desdemona · Juliet · Portia · Rosalind · Cupid · Belinda · Perdita · Puck · Mab |
| Major (spheroid) | Miranda · Ariel · Umbriel · Titania · Oberon |
| Outer (irregular) | Francisco · Caliban · Stephano · Trinculo · Sycorax · Margaret · Prospero · Setebos · Ferdinand |
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See also Rings of Uranus
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| The Solar System |
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| The Sun · Mercury · Venus · Earth · Mars · Ceres · Jupiter · Saturn · Uranus · Neptune · Pluto · Eris |
| Planets · Dwarf planets · Moons: Terrestrial · Martian · Asteroidal · Jovian · Saturnian · Uranian · Neptunian · Plutonian · Eridian |
| Small bodies: Meteoroids · Asteroids (Asteroid belt) · Centaurs · TNOs (Kuiper belt/Scattered disc) · Comets (Oort cloud) |
| See also astronomical objects, the solar system's list of objects, sorted by radius or mass, and the Astronomy Portal |
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