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 first planet discovered in modern times.
The blue color is because of methane gas in the atmosphere, which absorbs red and orange light strongly, leaving more blue light to be scattered to the observer.The clouds are thought to be mostly methane ice.
Uranus was found accidentally by William Herschel while he was searching the sky with a telescope on March 13, 1781. It had actually been seen many times before but dismissed as a star.
Facts:-
Sign:
Orbit:2,870,990,000 km (19.218 AU) from Sun
Diameter:51,118 km (32,000 miles) (equatorial)
Mass:8.683e25 kg (14.5 x Earth's)
Density:1,270 kg/m^3
Minimum Distance from Sun: 2.7 billion km
(1.7 billion miles)
Maximum Distance from Sun:3 billion km
(1.87 billion miles)
Minimum Distance from Earth:2.57 billion km
(1.6 billion miles)
Rotation Period about Axis:17.24 hrs (retrograde?)
Revolution Period about the Sun:84 years
Tilt of Axis:98o (or 82o?)
Surface Gravity:8.69 m/s^2 (0.89 x Earth's)
Temperature at Cloud Tops:-200o C ( -328o F)
Average Cloud Top Temperature (K):73K
Name in Roman/Greek Mythology:Uranus/Uranus
Satellites/Rings:21 known moons, faint rings
Careful pronunciation may be necessary to avoid embarrassment; say "YOOR a nus" , not "your anus" or "urine us".
Our only direct spacecraft observation of Uranus came from Voyager 2 Jan 24, 1986
General Feautures of Uranus:-
Uranus is the 3rd of the Gas Giant planets.It is barely visible from the Earth without a telescope, which explains why it was not known as a planet to the ancients, and why it had been observed various times after the telescope had been invented without the observers realizing that it was a planet and not a star.
The density is about 1.2 g/cc, implying that it is mostly hydrogen and helium. The mass is about 15 times that of the Earth, which makes it the 4th most massive planet. But its radius of about 4 times that of the Earth makes it the 3rd largest planet, since Neptune has a smaller radius but larger mass (because Neptune's density is higher). The rotation axis is unusual in that it lies only 8 degrees out of the plane of the orbit. Thus, at times the rings and the orbits of the moons appear like a "bulls-eye" when viewed from the Earth. The average rotational period is a little over 17 hours, and its orbital period is 84 years, at a mean separation of 19.2 A. U. from the Sun.
The rings are less extensive than those of Saturn, and may be rock rather than ice. There are 5 large moons and 10 small ones.
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.By 2007 the Sun will be directly over Uranus's equator.
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).
The Surface And Interior:-
Uranus has a relatively featureless appearance at visible wavelengths. Even from Voyager 2 at a distance of 80,000 km there were few distinguishable features. This is believed to be due to Uranus being further from the Sun than Jupiter and Saturn, which means its temperature is lower (only 58 degrees Kelvin in the upper atmosphere). This decreases the liklihood of chemical reactions making the colorful compounds that give the surface features on Jupiter and Saturn. In addition, the upper atmosphere is thought to have a high-level petrochemical haze that obscures features lower in the atmosphere.
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.
The Atmosphere:-
Uranus' atmosphere is about 83% hydrogen, 15% helium and 2% methane.
Uranus' Magnetosphere:-
Uranus' magnetic field is odd in that it is not centered on the center of the planet and voyager 2 confirmed the suspicion that Uranus had a magnetic field. The field is about 50 times stronger than that of the Earth and is tilted about 60 degrees with respect to the rotation axis. As a result, the magnetic field moves like a corkscrew as Uranus rotates. One hypothesis for this behavior of the magnetic field is that it originates in a thin conducting shell outside the core of the planet rather than deep in the core as for the Earth or Jupiter. The pressure would not be high enough for the relevant conducting material to be metallic hydrogen. A mixture of water, methane, and ammonia under sufficient pressure could provide the requisite electrical conductor.
The magnetosphere contains belts of charged particles similar to those of the Earth. The rings and most of the moons orbit within the magnetososphere and thus are protected from the Solar wind.
The 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 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.
The rings of Uranus are shown in the adjacent Hubble Space Telescope image. The rings were discovered from the Earth in 1977 when Uranus occulted (passed in front of) a star and it was noticed that there were dips in the brightness of the star before and after it passed behind the body of Uranus.
Most of the rings are not quite circular, and most are not exactly in the plane of the equator. The rings vary in brightness with angle around the moon, apparently because they vary in width with angle. The rings are very narrow (some only a few kilometers across) and no material can be detected in the regions between the rings. It is speculated that this stability of the narrow rings may be due to small "shepherding satellites".
Uranus' Moons:-
The following image shows the 5 largest satellites of Uranus: Miranda, Ariel, Umbriel, Titania, and Oberon. There are 10 additional small satellites.
Uranus has 20 named moons plus 1 recently discovered one which as yet has not been given an official name.
They form three distinct classes:
the 11 small very dark inner ones discovered by Voyager 2, the 5 large ones, and the newly discovered much more distant ones.
Most have nearly circular orbits in the plane of Uranus' equator (and hence at a large angle to the plane of the ecliptic); the outer 4 are much more elliptical.
The most interesting moon geologically is Miranda, shown on the left. Even though it is only 500 km in diameter, it shows surface geological features that are as varied as any site in the Solar System.
It is not clear why Miranda has been so active geologically.
Some theories invoke tidal heating effects earlier in its history, or a collision that tore it apart and allowed it to coelesce again. None are very conclusive.
