Uranus

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).

Click on an Object

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 or The Georgian Planet in honor of his patron 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.

Distance from Sun:
Mean:	19.19 AU
Perihelion:	2,741.30 x 10⁶ km
Ahelion:	3,003.62 x 10⁶ km
Size:
Volume:	6,833 x 10¹⁰ km³
Diameter:	51,118 km
Mass:	8.686 x 10²⁵ kg
Motion:
Year:	84.07 E Years
Day:	17.25 E Hours
Other:
Density:	1,270 kg per m³
Surface Temperature:	-220°C or 53°K

Uranus and Ariel 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 reason for this is unknown.

Actually, there's an ongoing battle over which of the poles is the actual 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. It's core 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' atmosphere is about 83% hydrogen, 15% helium and 2% methane.

Missions to Uranus

Uranus is the second farthest planet from us so it's not an easy trip to make. We only sent one probe and flew by giving us most of what we know about the planet.