PLANET URANUS

Planet Uranus is the seventh planet from the Sun. It is a gas giant, the third largest by diameter and fourth largest by mass. It is named after Uranus, the Greek god of the sky and progenitor of the other gods. 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.

Discovery and naming of Planet Uranus:
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." 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. Finally, Bode, as editor of the Berliner Astronomisches Jahrbuch, opted for Uranus, 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. The name was in use in Germany at least as far back as 1791, however. 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.

Composition of Planet Uranus:
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).

Axial tilt of Planet Uranus:
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.
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




Magnetic field of Planet Uranus:
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 of Planet Uranus:
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.

Rings of Uranus of Planet Uranus:
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 detected when Voyager 2 passed Uranus in 1986. As of 2005, 13 rings had been identified. In December 2005, the Hubble Space Telescope photographed a pair of previously unknown rings. The largest is twice the diameter of the planet's previously known rings. The new rings are so far from the planet that they are being called Uranus' "second ring system." Hubble also spotted two small satellites. One shares its orbit with one of the newly discovered rings. The new data reveals that the orbits of Uranus' family of inner moons have changed significantly in the last decade.

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Uranus' 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.

Visibility of Planet 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 (because of its faintness and slow apparent motion, it was never recognised as a planet by the Ancients); it is an easy target with binoculars. From Earth, it has a diameter of four arc-seconds. In larger amateur telescopes with an objective diameter greater than 12" (30 cm) the planet appears as a pale blue disc with distinct limb darkening, and two of the larger satellites, Titania and Oberon, may be visible. Even in large professional instruments no details can be seen on its disc. However, infrared studies of its atmosphere using adaptive optics have yielded interesting data in the years since the Voyager flyby.[



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