Uranus

Uranus is the seventh planet from the Sun and the first discovered in recent times. It is a gas giant and is larger than Neptune but less massive. It is the third largest planet and has a ring system, which was discovered second to Saturn's. It isn't easy to find with the naked eye, even on a clear night, but small telescopes will show a disc.

Uranus was Greek god of the heavens, son of Gaia and was overthrown by his son Kronos.

Uranus isn't eccentric; its path is almost a perfect circle. Strangely though, Uranus' axis of rotation is almost parallel to the ecliptic plane. Uranus has 27 moons.

Semimajor axis (km) 2872.46x106 Perihelion (km) 2741.30x106 Aphelion (km) 3003.62x106 Mean orbital speed (km s-1) 6.81 Sidereal orbit period (days) 30685.4 Tropical orbit period (days) 30588.74 Synodic period (days) 369.66 Length of day (hours) 17.24 Sidereal rotation period (hours) 17.24 Obliquity to orbit (deg) 97.77

Semimajor axis (AU) 19.19126393 Eccentricity 0.04716771 Inclination (deg) 0.76986 Longitude of ascending node (deg) 74.22988 Longitude of perihelion (deg) 170.96424 Mean longitude (deg) 313.23218 Discoverer William Herschel Date of Discovery 13 March 1781 J2000 Data from NSSDC

Only Voyager 2 has been to Uranus, launched 1977 and coming within 81,500 km during the January 24, 1986 flyby. The craft discovered the 98 degree tilt of the axis of rotation, nine rings around Uranus and an extra ten moons. It also found cliffs reaching nearly 20 km from the surface of Miranda.

There are 11 known rings and the brightest and outermost ring is called the Epsilon ring.

Uranian atmosphere, by composition, is 83% hydrogen, 15% helium and 2% methane although traces of other hydrocarbons have been found. Uranus appears blue because methane at high altitudes absorbs the red part of sunlight. Although Uranus appears all one colour, faint bands observed by the Hubble Space Telescope show winds of up to 160 ms^-1 at middle latitudes.

Mass (kg)	8.6832x1025
Equitorial radius (1 bar) (km)	25559
Polar radius (1 bar) (km)	24973
Mean density (kg m-3)	1270
Equatorial (1 bar) gravity (m s-2)	8.87
Escape Velocity (km s-1)	21.3
Black-body temp (K)	58.2
Solar intensity (W m2)	3.71
Natural satellites	27

Uranus has an odd magnetic tail because of the tilt of its rotational axis and also its magnetic field (about 60 deg from the rotational axis). It is currently uncertain what causes the magnetic field.