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Uranus

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Uranus

 

Diameter: 50,724 km
Distance from Sun: 2,877,000,000 km
Surface area: 8,083,079,690 km²
Length of day: 0d 17h 14m
Gravity: 8.69 m/s²
Circumference: 159,354 km
Mass: 86.81E24 kg (14.54 Earth mass)
Length of year: 84 years
Surface temp: -153 to -218 C

Uranus is the seventh planet from the Sun  and the  third largest (by diameter). Uranus is larger in diameter  but smaller in  mass than Neptune.

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.

Uranus small image

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.

Uranus taken from HST

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.  Recent observations with HST  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 from Voyager 2

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.

Uranus's rings

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 13 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.

Uranus’ Satellites

Uranus has 27 named moons.

 

 

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