Uranus

Uranus is the seventh planet from the sun in our solar system. This gas giant is the third-largest planet in our Solar System (after Jupiter and Saturn). Uranus is about 31,690 miles (51,118 km) in diameter. This is about 4 times the diameter of the Earth. This huge, icy planet is covered with clouds and is encircled by a belt of 11 rings and 22 known moons. Uranus' blue color is caused by the methane (CH4) in its atmosphere; this molecule absorbs red light, but (like Neptune) contains higher proportions of heavy elements than Jupiter or Saturn.

Uranus' rotational axis is strongly tilted on its side (97.9°). Instead of rotating with its axis roughly perpendicular to the plane of its orbit (like all the other planets in our Solar System), Uranus rotates on its side (along its orbital path). This tipped rotational axis gives rise to extreme seasons on Uranus.

Because of its almost-perpendicular axis orientation, there is a debate over which of Uranus' poles is its north pole. This debates leads to yet another: Is Uranus spinning in a retrograde orbit (like Venus) or not (like the other planets)?

Although Herschel discovered two of the planet's satellites, most of the rest were spotted by Voyager II. The total number of moons for Uranus is 21, the largest number for any planet in our solar system. With the help of more powerful telescopes, more moons may be revealed. In 1977, scientists from Cornell University watched as Uranus appeared to blink several times. They later realized the blinking was caused by a band of rings surrounding the planet.

The brightness of Uranus is between magnitude +5.5 and +6.0, so it can be seen with the naked eye as a faint star under dark sky conditions. It can be easily found with binoculars.

From Earth, it has a diameter of four arc-seconds. In larger amateur telescopes with an objective diameter greater than 12" (30cm) the planet appears as a pale blue disc with distinct limb shading, and two of the larger satellites, Titania and Oberon, may be visible. Even in large professional instruments no details can be seen on its disc. However, infrared studies of its atmosphere using adaptive optics have yielded interesting data in the years since the Voyager flyby.