Basic Data

• Mean Distance from Sun: 2876.7 million km.
• Equatorial Radius: 25,559 km. (4.01 Earth)
• Mass: 8.68 x 10²⁵ kg. (14.5 Earth)
• Surface Gravity: 8.7 m/s² (0.87 Earth)
• Length of Year: 84.32 years
• Length of Day: 17h 14m

Wikipedia - Uranus

About Uranus

One of the more humorous issues with this planet is the pronunciation of its name. For decades there has been the running debate over whether you say "your anus" or "urine us". Either one can bring snickers from an audience of the unsophisticated. Suffice it to say that I am not going to address that question here. As you read this page, pronounce it however you like. This is a visual/textual medium, not audio. You are on your own.

Uranus was the first planet discovered in modern times. All of the previous ones were known to ancients. Orbiting twice the distance from the Sun as Saturn, it receives only a fourth of the sunlight, and is smaller, so it has less reflecting area. Uranus is almost exactly four times the diameter of Earth. Being smaller than Jupiter or Saturn, it contains a correspondingly smaller percentage of hydrogen and helium, and a larger percentage of heavier gases, such as methane, and ices, such as water and ammonia. Unlike the larger gas giants with their yellow hues, Uranus has a greenish color.

The standard model of Uranus' structure postulates a small, rocky core, an outer atmosphere (which is what we actually see) with several layers of clouds, and a large mantle composed mainly of water, ammonia and other trace components. This mantle is liquid throughout most of its depths, and is sometimes referred to as a "water-ammonia ocean". This ocean, by the way, is actually quite hot and dense; only pressure keeps it from boiling into gas.

Uranus is also odd in one very particular way; it is tipped over on its side. The rotational pole is tilted at more than 90 degrees. When Voyager 2 passed by in 1986, the south pole was pointed almost directly at the sun. The planet's moons and faint rings also lie in equatorial orbits, which made the entire system resemble a target with a bullseye to the approaching space probe.

Uranus' Moons

Before Voyager 2 arrived, Uranus was known to have five moons. None of them are giant satellites, such as Jupiter's four or Saturn's Titan. In order of distance from Uranus, they are Miranda, Ariel, Umbriel, Titania and Oberon. Titania is the largest, being just a bit bigger than Saturn's Rhea. Because Voyager was forced by Uranus' odd axial tilt to make only one close pass to a moon, and because the mission planners also wanted to send the spacecraft on to Neptune, it only managed to get close up views of Miranda, the smallest of the five. Surprisingly, Miranda turned out to be the most interesting of all, with an odd surface geology that is still only partially understood.

During and since Voyager's visit, many more satellites have been discovered—all of them essentially small, irregular rocks—bringing the total up to 27.

Observation from Earth

Uranus was the first planet discovered by telescope, since it is very faint. Actually, it is visible to the naked eye under good conditions, and can be easily seen in a pair of binoculars. However, due to its slow motion across the sky and the fact that it does not stand out against the background, its true nature was not recognized until William Herschel observed it in the late 18th century. Even then, he thought at first that it was a comet, and it wasn't until several other astronomers began to suspect that it was a planet that he changed his mind.

Since its discovery, Uranus has been extensively studied using telescopes, and in recent decades, observed through the Hubble Space Telescope and visited by a flyby space probe.

Exploration of Uranus

Voyager 2 is the only probe to have visited Uranus so far. At this time, no other probes are yet planned. Maybe someday…