NASA Voyager 2 Image of the planet Uranus
|Faraway Mystery Planet Uranus|
Seventh Planet from the Sun
The planet Uranus, with its moons and rings, orbiting as they do at the far reaches of our Solar System, is the third most distant planet from the Sun.
Voyager 2 image of Uranus
Uranus is about 1.8 billion miles from the Sun. That is about 2.9 billion kilometers or just over 19 astronomical units (AU) from the Sun. It takes slightly more than 84 years for Uranus to complete one circuit around the Sun.
It is the seventh planet out from the Sun. Earth is third out from the Sun.
Among the known planets of the Solar System, Uranus is the third largest in diameter. It's 31,763 miles (51,118 km) in diameter at the equator. Uranus is larger in diameter, yet smaller in mass than the planet Neptune. Its mass is 14.6 times that of Earth.
The length of a Uranus day is 17.24 hours. Uranus is four times the size of Earth.
The planet does have a magnetic field, but it's tilted 60 degrees away from the axis upon which Uranus rotates making it unreadable from Earth. That tilt may mean the magnetic field is undergoing a planet-wide polarity shift.
The name. The planet was seen first in 1690 by John Flamsteed, but he thought it was a star. He cataloged it as 34 Tauri.
Later it became the first planet discovered in modern times when it was spotted by William Herschel as he searched the sky with his homemade telescope on March 13, 1781. He understood it was not a star and named it the Georgian Planet in honor of his patron, King George III of England. Others at that time called the planet Herschel.
Because the name Uranus conformed with the other planet names from classical mythology, it came into common use around 1850.
Uranus was the god of the heavens in ancient Greek mythology. He was the earliest supreme god.
When pronouncing the name of the planet, the emphasis is on the first syllable. Say "YOUR uh nus."
Moons of Uranus. We know Uranus has at least 27 moons. Before the planet was visited by the spacecraft Voyager 2 on January 24, 1986, astronomers knew of only five. Voyager 2 discovered ten small moons. More have been found subsequently. Today, astronomers suggest there may be more tiny satellites among the planet's rings.
The moons of Uranus are eye-openers. They have statuesque mountains towering more than ten miles high. Incredibly deep valleys. Vast plains, some with a mysterious dark surface. Moon diameters range from a bit fatter than 25 miles up to about 1,100 miles.They circle Uranus in orbits ranging from every eight hours to every 14 days. Some of the moons are very tiny.
List of Uranus moons »
Voyager moons. The interplanetary probe Voyager 2 flew within 50,600 miles of Uranus' cloud tops on January 24, 1986, discovering a magnetic field and much ultraviolet light, known as dayglow.
Uranus moons Umbriel (left) and
Ariel (right) in 1986 Voyager 2 photos
click to enlarge
Voyager 2 found 10 previously-unknown moons, the largest only 90 miles in diameter, bringing the total to 15. Astronomers previously had seen five large ice-and-rock moons. The innermost, Miranda, was found by Voyager to be one of the strangest bodies in the Solar System, with fault canyons up to 12 miles deep, terraced layers and mixed young and old surfaces.
Titania was marked by huge faults and deep canyons. Ariel had the brightest and youngest surface of Uranian moons, with many deep valleys and broad ice flows. Dark-surfaced Umbriel and Oberon looked older.
The moons Umbriel and Ariel each are about 75O miles in diameter. In NASA's 1986 pictures at right, Voyager 2 was about 346,000 miles from Umbriel. The Ariel picture is a mosaic of four images collected when Voyager 2 was about 8O,OOO miles from the moon
List of Uranus moons »
Lots and lots of moons. There are at least 156 moon in the Solar System. With a total of 63, Jupiter currently has the most known natural satellites of any planet in the Solar System. Saturn is second with 47. Uranus has 27. Neptune has 13. Pluto has 3. Mars has 2. Earth has 1.
New moonlet, in white circle, orbiting Uranus, bottom left
International Astronomical Union illustration
The moon totals for Jupiter, Saturn, Uranus, Neptune and Pluto can be expected to increase as more powerful telescopes become available in the future.
Rings of Uranus. Uranus has more than a dozen known rings. The first ring discoveries were made in the 1970s. Later, while looking at the rings around Uranus in 1986, the Voyager spacecraft uncovered strange incomplete-circle partial formations now called ring arcs. Uranus' many rings and arcs varied in depth and density.
Voyager found nine rings around Uranus, but they were quite different from Jupiter and Saturn rings. Some of Uranus' rings may be young remnants of a shattered moon.
After passing Uranus, Voyager 2 sailed on toward a rendezvous within 3,000 miles of the planet Neptune in August 1989.
The distant planet continues to surprise astronomers. Using the Hubble Space Telescope in 2005, astronomers uncovered another pair of giant rings girdling the planet.
Hubble Space Telescope image of a Uranus ring
The largest of the newly-discovered rings is twice the diameter of the planet's previously known ring system.
The Hubble discoveries suggest Uranus has a young, dynamic system of rings and moons. Unlike the famous rings around Saturn, the rings around Uranus are dim and dark because they are mostly dust rather than ice.
Due to the extreme tilt of Uranus's axis, the rings appear to be nearly perpendicular relative to rings around other gas giant planets like Saturn.
Lightning On Uranus. French scientists listening to radio signals recorded in 1986 at Uranus by the U.S. Voyager 2 spacecraft heard lightning bolts.
The same kind of static crashes heard in an AM radio during an electrical storm on Earth were found among data transmitted back to Earth from Uranus.
Apparently the lightning strikes on Uranus are more powerful than those on Earth, but nowhere near as strong as the magnificent electrical discharges on Saturn. The bolts are giant sparks of static electricity generated by turbulence in the Uranian atmosphere.
When electricity flows, it generates electromagnetic radiation. We call such energy a radio wave. A radio wave can be controlled by man using a transmitter to generate a signal. The signal can be modulated with sounds or made to carry other forms of information. On the other hand, when electromagnetic energy is not controlled, we call it noise or static. Lightning is merely a very large, uncontrolled burst of static.
The Voyager spacecraft's receiver heard strong static as it sailed past Uranus. The chaotic signals received had the same characteristics as lightning noise.
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