Uranus (planet)

Uranus is the seventh planet from the Sun in our solar system. It is a gas giant (also known as a Jovian planet, after the planet Jupiter).

Voyager 2 photo of Uranus taken in 1986

Uranus is so far away from the sun that it takes 84 years on Earth to complete one orbit. In other words, a year on Uranus is equal to 84 years on Earth.

Uranus was discovered without the use of a telescope by astronomer William Herschel in 1781.

Parameters for classification as a planet

Uranus is classified as a planet by the International Astronomical Union for meeting the following criteria:

• Orbits the sun;
• Has mass sufficient for its gravity to form a nearly round shape;
• Has mass sufficient for gravity to clear a path in its orbit.

Physical Characteristics

Uranus's distance from the sun is about nineteen and a half times that of earth , has a volume 63.1 times the volume of the Earth a diameter of 1.60592 x 10⁵ km and with a mass fourteen times that of Earth (14 Earth masses or 8.6849 X 10²⁵ kg), is the lightest of the outer planets. It has a smaller surface gravity, about 86% of Earth's.

It has a much colder core than the other gas giants and radiates very little heat into space.

Uranus has no solid surface. Eighty percent or more of Uranus is an extended liquid core of icy materials composed of water, ammonia and methane and higher density materials beneath.

The atmosphere is composed of mainly of hydrogen and helium and has a temperature of about -216 °C. Its atmosphere has small amounts of methane, water and ammonia. Uranus gets its blue-green colour from a combination of light absorbed by the methane layer and light reflected by clouds beneath the methane. The sunlight passes through the methane, is then reflected by the clouds back through the methane layer where the red light portion of the spectrum is absorbed leaving only the blue-green spectrum to pass through, making the atmosphere appear blue-green.

Rotational Characteristics

Uniquely among the planets, it orbits the Sun on its side with the poles pointing in the axial plane almost directly at the sun in the orbital plane; its axial tilt is over ninety degrees to the ecliptic. While its polar orientation switches back and forth as it orbits the sun, this means that the seasons last for extreme periods of time, winter for example lasting 42 earth years.

Natural satellites

Uranus has twenty-seven satellites, all named after Shakespearean characters, the largest being Titania, Oberon, Umbriel, Ariel and Miranda. Unlike some moons of the other giant planets and Earth's, none of them are larger than the dwarf planets Eris and Pluto.

NASA Hubble Space Telescope: Graphic depiction of the two rings and the moons of Uranus