Uranus

Once considered one of the blander-looking planets, Uranus (pronounced YOOR un nus) has been revealed as a dynamic world with some of the brightest clouds in the outer solar system and 11 rings. The first planet found with the aid of a telescope, Uranus was discovered in 1781 by astronomer William Herschel. The seventh planet from the Sun is so distant that it takes 84 years to complete one orbit. Uranus, with no solid surface, is one of the gas giant planets (the others are Jupiter, Saturn, and Neptune).

The atmosphere of Uranus is composed primarily of hydrogen and helium, with a small amount of methane and traces of water and ammonia. Uranus gets its blue-green color from methane gas. Sunlight is reflected from Uranus' cloud tops, which lie beneath a layer of methane gas. As the reflected sunlight passes back through this layer, the methane gas absorbs the red portion of the light, allowing the blue portion to pass through, resulting in the blue-green color that we see. The planet's atmospheric details are very difficult to see in visible light. The bulk (80 percent or more) of the mass of Uranus is contained in an extended liquid core consisting primarily of 'icy' materials (water, methane, and ammonia), with higher-density material at depth.

In 1986, Voyager 2 observed faint cloud markings in the southern latitudes blowing westward between 100 and 600 kilometers (60 and 400 miles) per hour. In 2004, the Keck Observatory in Hawaii used advanced optics to capture highly detailed images of Uranus as the planet approached its southern autumnal equinox, when the equator will be vertically illuminated by the Sun.

Uranus' rotation axis is nearly horizontal as though Uranus has been knocked on its side, as compared to most other planets in our solar system. This unusual orientation may be the result of a collision with a planet-sized body early in the planet's history, which apparently radically changed Uranus' rotation. Additionally, while magnetic fields are typically in alignment with a planet's rotation, Uranus' magnetic field is tipped over: instead of aligning along the rotational axis, the magnetic axis is tilted nearly 60 degrees from the planet's axis of rotation, and is also offset from the center of the planet by one-third of the planet's radius. Unlike the magnetic fields of Earth, Jupiter, and Saturn, which can be thought of as acting like dipole bar magnets, the fields of Uranus (and Neptune also) are very irregular. Uranus' magnetic field is about 48 times more powerful than Earth's.

Even though Uranus is tipped on its side and experiences seasons that last over 20 years, the temperature differences on the summer and winter sides do not differ greatly because the planet is so far from the Sun. Near the cloud tops, the temperature of Uranus is -216 degrees Celsius (-357 degrees Fahrenheit).

Because of the planet's unusual orientation, Uranus' rings are perpendicular to its orbital path about the Sun. The 10 outer rings are dark, thin, and narrow, while the 11th ring is inside the others and is broad and diffuse. Uranus has 27 known moons, named mostly for characters from the works of William Shakespeare and Alexander Pope. Miranda is the strangest-looking Uranian moon, appearing as though it were made of spare parts. The high cliffs and winding valleys of the moon may indicate partial melting of the interior, with icy material occasionally drifting to the surface.

KEY FACTS:

Uranus is the seventh planet from the sun in our solar system. 

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.

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.

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)? 

Uranus is about 31,690 miles (51,118 km) in diameter. This is about 4 times the diameter of the Earth.

This gas giant is the third-largest planet in our Solar System (after Jupiter and Saturn). 

 Uranus' mass is about 8.68 x 10²⁵ kg. This is about 14 times the mass of the Earth. The gravity on Uranus is only 91% of the gravity on Earth. A 100-pound person on Uranus would weigh 91 pounds. 


Each day on Uranus takes 17.9 Earth hours. A year on Uranus takes 84.07 Earth years; it takes 84.07 Earth years for Uranus to orbit the sun once. 


 Uranus is over 19 times as far from the Sun as the Earth is; it averages 19.18 A.U.

At aphelion (the farthest point in its solar orbit) it is 1,850,000,000 miles (3,003,000,000 km) from the Sun. At perihelion (the closest point in its solar orbit) it is 1,700,000,000 miles (2,739,000,000 km) from the Sun.


The mean temperature on the surface of Uranus' cloud layer is -350°F (59 K). Uranus radiates very little heat in comparison with the other gas giants, Jupiter, Saturn and Neptune).


Uranus is a frozen, gaseous planet with a molten core. Uranus' atmosphere consists of 83% hydrogen, 15% helium and 2% methane.

Uranus has 5 large moons (2 were discovered by Wm. Herschel in 1781, 2 were discovered by Wm. Lassell in 1851, and one by G. Kuiper in 1948) and many small moons (which were discovered much later).

Uranus was discovered by the British astronomer William Herschel on March 13, 1781. Herschel also discovered two of the moons of Uranus (Titania and Oberon) and some of the moons of Saturn.

This planet was originally named in 1781 by the British astronomer William Herschel - he called it Georgium Sidus (meaning "the Georgian planet") to honor the King George III of England. The name was later changed to Uranus, the ancient mythological god of the sky, Ouranos. The name Uranus was suggested by the German astronomer Johann Elert Bode.

Uranus has been visited by NASA's Voyager 2, whose closest approach was on January 24, 1986.