Uranus

Uranus is barely visible to the naked eye in very clear night, it appears, even with powerful tools that as a small greenish disk. Uranus is the seventh planet of the solar system, a gas giant and the third in size. The blue-green coloration results from the absorption bands of methane. Its appearance reflects the presence of a high-altitude hydrocarbon photochemical haze overlying clouds of methane, which in turn overlie clouds of hydrogen sulfide and/or ammonia. Uranus was discovered March 13, 1781 by William Herschel. Uranus is 3 times smaller than Jupiter. Named comes from the god Uranus, Roman god of the sky, equivalent to the Greek god Ouranos.
Uranus has a rotation axis tilted at 98° (The Earth is 23.27 °, and that of Jupiter of 3.22 °). Uranus is almost lying on its orbit. Uranus is a gas giant planet, like Jupiter, Saturn and Neptune. In theory, it would consist of a solid core of iron and silicates of about 7 500 km in diameter, surrounded by a mantle composed of molecular hydrogen, helium, methane and ammonia on a thickness of 10 000 km, then a surface layer of liquid hydrogen and helium, thickness of about 7 600 km merges gradually into the atmosphere. Unlike Jupiter and Saturn, Uranus is not massive enough that hydrogen exists in the metallic state around the core.

"A planet is a celestial body that is in orbit around the Sun, which has sufficient mass for its gravity to overcome the cohesive forces of the solid body and maintain hydrostatic equilibrium (spherical), and that eliminated any body moving in an orbit close ".
This definition was approved August 24, 2006, at the 26th General Assembly of the IAU (International Astronomical Union) by a show of hands of about 400 scientists and astronomers after ten days of discussions. This is Friedrich Wilhelm Herschel who discovered Uranus by accident March 13, 1781 and he thinks at first to deal with a comet. Uranus had been observed before but it was ignored, and cataloged as simply another star (the first recorded sighting of Uranus date in 1690 when John Flamsteed cataloged it as 34 Tauri star). Having correctly identified the nature of the star, Herschel called the Georgian Planet in honor of King George III of England. The name Uranus was first proposed by Johan Elert Bode in conformity with the names of other planets and admitted until 1850. Uranus showed irregularities in its orbit around the Sun that could explain the law of universal gravitation.

He had an eighth planet to explain these irregularities. A lock psychological jumped, the dimensions of the solar system at once doubled.
Most planets spin on an axis nearly perpendicular to the plane of the ecliptic but Uranus' axis is almost parallel to that plane.
Uranus' atmosphere is constituted of about 83% hydrogen, 15% helium and 2.3% methane.
Uranus is composed of a solid core and iron silicate of about 7500 km in diameter, surrounded by a coat composed of ice water mixed with helium, methane and ammonia to a thickness 10 000 km, then a surface layer of liquid hydrogen and helium, thickness of about 7600 km.
Uranus' blue color is the result of absorption of red light by methane in the upper atmosphere. Uranus has rings like other gas giant, its rings were not discovered until 1979. They are very dark as those of Jupiter and composed of relatively large particles, up to 10 meters in diameter in addition to fine dust, like the rings of Saturn. There are 11 known rings, all very low, the brightest being the epsilon ring.

Uranus is unique in the solar system because the inclination of its axis of rotation is about 98°, i.e. it is practically lying on the plane of revolution around the Sun. The geographic poles face the sun while on the other planets they are perpendicular to the plane of rotation. Solar flares also reach Uranus, this is how the astronomer Laurent Lamy, of the Paris Observatory, observed the aurora on Uranus.
Thanks to the Hubble Space Telescope has obtained the magnificent image of the distant Uranus.
The aurora of Uranus appeared on these two images as point light sources and not as large as arcs on other planets. A few days apart, the space telescope has captured the appearance of auroras at the poles of the magnetic field of the giant planet.
The magnetic poles of the planet are located at 60° of its geographic poles.