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Uranus

AstronomyPlanetsScience
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Table of Contents
  • Introduction
  • Rotational Axis
  • Size
  • Mass and Gravity
  • Length of a Day and Year
  • Orbit Distance
  • Temperature
  • Planetary Composition and Atmosphere
  • Rings
  • Moons
  • Discovery
  • Uranus-Earth Comparison
  • Name and Symbol
  • Spacecraft Visits
  • Activities and Links

Introduction

Saturn Saturn Uranus is the seventh planet from the sun in our solar system. This huge, ice giant 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.

Rotational Axis

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. For more information on Uranus’ extreme seasons, click here.

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)?

Size

Uranus size compared to Earth 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).

Mass and Gravity

Uranus Mass 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. This is because it is such a large planet (and the gravitational force a planet exerts upon an object at the planet’s surface is proportional to its mass and to the inverse of its radius squared).

A 100-pound person on Uranus would weigh 91 pounds.

Length of a Day and Year

hourglass 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.

Orbit Distance

Uranus Orbit 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.

Temperature

thermometer 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).

Planetary Composition and Atmosphere

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

For more information on Uranus’ composition, click here.

Rings

Uranus Rings

Uranus and its rings
photographed by an infrared camera.

Uranus has a belt of 11 faint, narrow rings composed of rock and dust. They circle Uranus is very elliptical orbits. These rings are only a fraction of the size of Saturn’s rings, and were only discovered in 1977.

For more information on Uranus’ rings, click here.

Moons

Oberon - Uranus' largest moon

Oberon, the largest moon of Uranus.
Photo taken by NASA’s Voyager mission in 1986.

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).

For more information on Uranus’ moons, click here.

Discovery

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.

Uranus-Earth Comparison

Uranus Earth comparison graph

Name and Symbol

Uranus Symbol

This is the symbol of the planet Uranus.

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.

Spacecraft Visits

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

Activities and Links

  • Uranus coloring page
  • Find It!, a quiz on Uranus.
  • An interactive puzzle about Uranus
  • Uranus Cloze Printout: A fill-in-the-blanks activity on the planet Uranus.
  • How to write a report on a planet - plus a rubric.
Other Links:
Estimated Grade Level
Our subscribers' grade-level estimate for this page:
3rd - 5th
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Saturn
Uranus
Introduction
Seasons and Rotational Tilt
Atmosphere and Composition
Rings
Moons
Activities & Links
The Planets
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
(Pluto - dwarf planet)
Your weight on the planets
Your age on the planets
The Solar System
— Our Solar System —
The Sun
The Planets
The Moon
Asteroids
Kuiper Belt
Comets
Meteors
Zoom Astronomy
— All About Astronomy —
Table of Contents
Index
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