Introduction

Uranus is the seventh planet from the sun and it is the third largest in the history of the solar system. Uranus was discovered by About Uranus

Uranus is denser than Jupiter and Saturn and is composed of 83% hydrogen, 15% helium, 2% methane, a little acetylene and other hydrocarbons, substantial amounts of water, and probably some methane, ammonis, rock, and metal. Uranus has anequatoial diameter of 51,800 kilometers and orbits the sun once every 84.01 Earth years. Its has a distance from the sun of 2.87 billion kilometers. A day's lenght on Uranus is 17 hours and 14 minutes.

Methane in the upper atmosphere absorbs red lights, giving Uranus its blue-green color. The temperature in the upper atmosphere is only about 60 K, but the temperature increases with atmospheric depth. The atmosphere is arranged into clouds running at constant latitudes, similar to the orientation of the more vivid latitudinal bands seen on Jupiter and Saturn. Underneath the thick clouds there may be an immense ocean of water that, though it is heated to several thousand degrees Kelvin, does not boil away because of the intense pressure from the atmosphere above it. The core of the planet is most likely rocks and metals.

Uranus unusual position is thought to be the result of a collusion with a planet-sized body early in the solar system's history. Voyager2, found that one of the most striking influences of thissideways position is its effect on the tail of the magnetic field. Uranus' rotational axis is tilted an unusally great 98 degrees from a hypothetical line perpendicular to the ecliptic plane. (The ecliptic plane is the theoretical plane created by extending earth's orbits around the sun to form a vast, flat surface.) Thus, the planet lies on it's side with its north pole pointing slightly below the plane. During the course of it's 84-year orbit around the sun, Uranus points first one pole toward the sun, then its equator, and then the other pole. Uranus rotates in retrograde, or clockwise, motion about once every 17 hours.

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Uranus's Satellites

Uranus has fifteen known satlliets, which are composed mostly of ice and heavily cratered. The five major satellites are Miranda, Ariel, Umbriel, Oberon. Oberon's surface is very old and heavily cratered, indicating that the body has been geologically inactive during most of its existence. Titania is covered by only small craters and darkest satellites, respectively. Ariel has a young surface that contains some small craters, many faults, and some apparent ice flows. umbriel is uniformly very dark and heavily cratered. The darkness of the surface suggests that it is relatively young, but the large number of craters indicates that the surface is old. Miranda, the smallest and innermost of the major satellite, is partly young terrain covered with ridges and scarps and odly shaped, sharp-cornered regions. another part resembles the grooved terrain of Jupiter's Ganymede. A third area has a very old surface with many craters.

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Uranus' Rings

Uranus has a system of narrow, sharp-edged rings made of some unusally dark material very unlink Saturn's bright, icy rings. They are not uniformly thick, and in some places certain rings are so thin that they disappears. It is possible that Uranus' rings are relatively young compared to saturn's and are still being formed. In the 1977, the outermost epsilon ring is composed mostly of ice boulders several feet across. There may be a large number of norrow rings, or possibly incomplete rings or ring arcs, as small as fifty meters in width. At least one ring, the epsilon, was found to be gray in color.

Two spacecraft of NASA's Marine series, Voyager 1 and 2 were the first in that series to be sent to explore the outer solar system.

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Voyager 1/2 Closest Approach Distances/Times

Voyager 1/2 Closest Approach Distances/Times

                   Voyager 1                            Voyager 2
          Distance         Date/Time          Distance         Date/Time
Jupiter    4.89 Rj   March 5, 1979 12:05:26   10.11 Rj   July  9, 1979 22:29:51
Saturn     3.09 Rs   Nov. 12, 1980 23:46:30    2.67 Rs   Aug. 26, 1981 03:24:57
Uranus       ---              ---              4.19 Ru   Jan. 24, 1986 17:59:47
Neptune      ---              ---              1.18 Rn   Aug. 25, 1989 03:56:36

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This page was written by Lulama Cooper in the Astronomy Class of BCC/Broward County July 1998