Jumat, 30 Januari 2009

uranus

Uranus Astronomical symbol of Uranus
Uranus as seen by Voyager 2
Uranus, as seen by Voyager 2
Discovery
Discovered by William Herschel
Discovery date March 13, 1781
Designations
Adjective Uranian
Epoch J2000
Aphelion 3 004 419 704 km
20.083 305 26 AU
Perihelion 2 748 938 461 km
18.375 518 63 AU
Semi-major axis 2 876 679 082 km
19.229 411 95 AU
Eccentricity 0.044 405 586
Orbital period 30 799.095 days
84.323 326 yr
Synodic period 369.66 days[2]
Average orbital speed 6.81 km/s[2]
Mean anomaly 142.955 717°
Inclination 0.772 556°
6.48° to Sun's equator
Longitude of ascending node 73.989 821°
Argument of perihelion 96.541 318°
Satellites 27
Physical characteristics
Equatorial radius 25 559 ± 4 km
4.007 Earths[3][c]
Polar radius 24 973 ± 20 km
3.929 Earths[3][c]
Flattening 0.022 9 ± 0.000 8[b]
Surface area 8.115 6×109 km²[4][c]
15.91 Earths
Volume 6.833×1013 km³[2][c]
63.086 Earths
Mass (8.6810 ± 0.0013)×1025 kg
14.536 Earths[5]
GM=5 793 939 ± 13 km³/s²
Mean density 1.27 g/cm³[2][c]
Equatorial surface gravity 8.69 m/s²[2][c]
0.886 g
Escape velocity 21.3 km/s[2][c]
Sidereal rotation
period		 −0.718 33 day
17 h 14 min 24 s[3]
Equatorial rotation velocity 2.59 km/s
9,320 km/h
Axial tilt 97.77°[3]
North pole right ascension 17 h 9 min 15 s
257.311°[3]
North pole declination −15.175°[3]
Albedo 0.300 (bond)
0.51 (geom.)[2]
Surface temp.
1 bar level[7]
0.1 bar
(tropopause)[8]
min mean max

76 K
49 K 53 K 57 K
Apparent magnitude 5.9[6] to 5.32[2]
Angular diameter 3.3"–4.1"[2]
Atmosphere[8][9][10][d]
Scale height 27.7 km[2]
Composition (Below 1.3 bar)
83 ± 3% Hydrogen (H2)
15 ± 3% Helium
2.3% Methane
0.009%
(0.007–0.015%)		 Hydrogen deuteride (HD)[11]
Ices:

Ammonia

water

ammonium hydrosulfide (NH4SH)

methane (CH4)
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caelus

Caelus, also known as Coelus, was the Roman god of the sky, personified from the Latin word for "sky", caelum.[1] Caelus was later equated with the Greek god of the heavens, Uranus, who was vastly more important to the Greeks than Caelus was to the Romans.

In the Roman adaptation of Greek mythology, Caelus was, by marriage to Tellus (Greek: Gaia), the father of Saturn (Greek: Cronus), Ops (Greek: Rhea), Oceanus, and the other Titans, as well as the Gigantes. Alone, Caelus was the father of Venus (Greek: Aphrodite).

Caelus is often associated with the sign of the zodiac, Aquarius.

The Roman Caelus (or Caelum) is simply a translation of the Greek Uranus or Ouranos (Οὐρανός), not the name of a distinct national divinity. There is no evidence of the existence of a cult of Caelus, though the name occurs in dedicatory inscriptions, due to Oriental influences; the worship of the sky being closely connected with that of Mithras. Caelus is sometimes associated with Terra, represented in sculptural art as an old, bearded man holding a robe billowing over his head in the form of an arch, a conventional sign of deity.

[edit] Notes

  1. ^ This personification is indicated by the use of the masculine form caelus rather that the neuter, caelum

[edit] References

  • Grimal, Pierre (1986). The Dictionary of Classical Mythology (pp. 83–84). Oxford: Basil Blackwell. ISBN 0-631-13209-0.
This article relating to an Ancient Roman myth or legend is a stub. You can help Wikipedia by expanding it.
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caelus

Caelus, also known as Coelus, was the Roman god of the sky, personified from the Latin word for "sky", caelum.[1] Caelus was later equated with the Greek god of the heavens, Uranus, who was vastly more important to the Greeks than Caelus was to the Romans.

In the Roman adaptation of Greek mythology, Caelus was, by marriage to Tellus (Greek: Gaia), the father of Saturn (Greek: Cronus), Ops (Greek: Rhea), Oceanus, and the other Titans, as well as the Gigantes. Alone, Caelus was the father of Venus (Greek: Aphrodite).

Caelus is often associated with the sign of the zodiac, Aquarius.

The Roman Caelus (or Caelum) is simply a translation of the Greek Uranus or Ouranos (Οὐρανός), not the name of a distinct national divinity. There is no evidence of the existence of a cult of Caelus, though the name occurs in dedicatory inscriptions, due to Oriental influences; the worship of the sky being closely connected with that of Mithras. Caelus is sometimes associated with Terra, represented in sculptural art as an old, bearded man holding a robe billowing over his head in the form of an arch, a conventional sign of deity.

[edit] Notes

  1. ^ This personification is indicated by the use of the masculine form caelus rather that the neuter, caelum

[edit] References

  • Grimal, Pierre (1986). The Dictionary of Classical Mythology (pp. 83–84). Oxford: Basil Blackwell. ISBN 0-631-13209-0.
This article relating to an Ancient Roman myth or legend is a stub. You can help Wikipedia by expanding it.
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Selasa, 30 Desember 2008

URANUS

Uranus is the ancient Greek deity of the Heavens, the earliest supreme god. Uranus was the son and mate of Gaia the father of Cronus (Saturn) and of the Cyclopes and Titans (predecessors of the Olympian gods).

Uranus, the first planet discovered in modern times, was discovered by William Herschel while systematically searching the sky with his telescope on March 13, 1781. It had actually been seen many times before but ignored as simply another star (the earliest recorded sighting was in 1690 when John Flamsteed cataloged it as 34 Tauri). Herschel named it "the Georgium Sidus" (the Georgian Planet) in honor of his patron, the infamous (to Americans) King George III of England; others called it "Herschel". The name "Uranus" was first proposed by Bode in conformity with the other planetary names from classical mythology but didn't come into common use until 1850.

Uranus has been visited by only one spacecraft, Voyager 2 on Jan 24 1986.

Most of the planets spin on an axis nearly perpendicular to the plane of the ecliptic but Uranus' axis is almost parallel to the ecliptic. At the time of Voyager 2's passage, Uranus' south pole was pointed almost directly at the Sun. This results in the odd fact that Uranus' polar regions receive more energy input from the Sun than do its equatorial regions. Uranus is nevertheless hotter at its equator than at its poles. The mechanism underlying this is unknown.

Actually, there's an ongoing battle over which of Uranus' poles is its north pole! Either its axial inclination is a bit over 90 degrees and its rotation is direct, or it's a bit less than 90 degrees and the rotation is retrograde. The problem is that you need to draw a dividing line *somewhere*, because in a case like Venus there is little dispute that the rotation is indeed retrograde (not a direct rotation with an inclination of nearly 180).

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 (and Neptune) are 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' atmosphere is about 83% hydrogen, 15% helium and 2% methane.

Like the other gas planets, Uranus has bands of clouds that blow around rapidly. But they are extremely faint, visible only with radical image enhancement of the Voyager 2 pictures (right). Recent observations with HST (left) show larger and more pronounced streaks. Further HST observations show even more activity. Uranus is no longer the bland boring planet that Voyager saw! It now seems clear that the differences are due to seasonal effects since the Sun is now at a lower Uranian latitude which may cause more pronounced day/night weather effects. By 2007 the Sun will be directly over Uranus's equator.

Uranus' blue color is the result of absorption of red light by methane in the upper atmosphere. There may be colored bands like Jupiter's but they are hidden from view by the overlaying methane layer.

Like the other gas planets, Uranus has rings. Like Jupiter's, they are very dark but like Saturn's they are composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust. There are 11 known rings, all very faint; the brightest is known as the Epsilon ring. The Uranian rings were the first after Saturn's to be discovered. This was of considerable importance since we now know that rings are a common feature of planets, not a peculiarity of Saturn alone.

Voyager 2 discovered 10 small moons in addition to the 5 large ones already known. It is likely that there are several more tiny satellites within the rings.

Uranus' magnetic field is odd in that it is not centered on the center of the planet and is tilted almost 60 degrees with respect to the axis of rotation. It is probably generated by motion at relatively shallow depths within Uranus.

Uranus is sometimes just barely visible with the unaided eye on a very clear night; it is fairly easy to spot with binoculars (if you know exactly where to look). A small astronomical telescope will show a small disk. There are several Web sites that show the current position of Uranus (and the other planets) in the sky, but much more detailed charts will be required to actually find it. Such charts can be created with a planetarium program.
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