Uranus Facts

Uranus has a very unique rotation–it spins on its side at an almost 90-degree angle, unlike other planets.

Uranus is the seventh planet from the Sun and the third-largest (by diameter). Uranus is larger in diameter but smaller in mass than Neptune

Planet Profile

orbit: 2,870,990,000 km (19.218 AU) from Su
diameter: 51,118 km (equatorial)
mass: 8.683e25 kg

History of Uranus

Careful pronunciation may be necessary to avoid embarrassment; say “YOOR a nus” , not “your anus” or “urine us”.

Uranus is the ancient Greek deity of the Heavens, the earliest supreme god. Uranus was the son and mate of Gaia the father of Cronus (Saturn) and of the Cyclopes and Titans (predecessors of the Olympian gods).

Uranus, the first planet discovered in modern times, was discovered by William Herschel while systematically searching the sky with his telescope on March 13, 1781. It had actually been seen many times before but ignored as simply another star (the earliest recorded sighting was in 1690 when John Flamsteed cataloged it as 34 Tauri). Herschel named it “the Georgium Sidus” (the Georgian Planet) in honor of his patron, the infamous (to Americans) King George III of England; others called it “Herschel”. The name “Uranus” was first proposed by Bode in conformity with the other planetary names from classical mythology but didn’t come into common use until 1850.

Uranus has been visited by only one spacecraft, Voyager 2 on Jan 24 1986.

Most of the planets spin on an axis nearly perpendicular to the plane of the ecliptic but Uranus’ axis is almost parallel to the ecliptic. At the time of Voyager 2’s passage, Uranus’ south pole was pointed almost directly at the Sun. This results in the odd fact that Uranus’ polar regions receive more energy input from the Sun than do its equatorial regions. Uranus is nevertheless hotter at its equator than at its poles. The mechanism underlying this is unknown.

Actually, there’s an ongoing battle over which of Uranus’ poles is its north pole! Either its axial inclination is a bit over 90 degrees and its rotation is direct, or it’s a bit less than 90 degrees and the rotation is retrograde. The problem is that you need to draw a dividing line *somewhere*, because in a case like Venus there is little dispute that the rotation is indeed retrograde (not a direct rotation with an inclination of nearly 180).

Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a little helium (in contrast to Jupiter and Saturn which are mostly hydrogen). Uranus (and Neptune) are in many ways similar to the cores of Jupiter and Saturn minus the massive liquid metallic hydrogen envelope. It appears that Uranus does not have a rocky core like Jupiter and Saturn but rather that its material is more or less uniformly distributed.

Uranus’ atmosphere is about 83% hydrogen, 15% helium and 2% methane.

Like the other gas planets, Uranus has bands of clouds that blow around rapidly. But they are extremely faint, visible only with radical image enhancement of the Voyager 2 pictures (right). Recent observations with HST (left) show larger and more pronounced streaks. Further HST observations show even more activity. Uranus is no longer the bland boring planet that Voyager saw! It now seems clear that the differences are due to seasonal effects since the Sun is now at a lower Uranian latitude which may cause more pronounced day/night weather effects. By 2007 the Sun will be directly over Uranus’s equator.

Uranus’ blue color is the result of absorption of red light by methane in the upper atmosphere. There may be colored bands like Jupiter’s but they are hidden from view by the overlaying methane layer.

Like the other gas planets, Uranus has rings. Like Jupiter’s, they are very dark but like Saturn’s they are composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust. There are 13 known rings, all very faint; the brightest is known as the Epsilon ring. The Uranian rings were the first after Saturn’s to be discovered. This was of considerable importance since we now know that rings are a common feature of planets, not a peculiarity of Saturn alone.

Voyager 2 discovered 10 small moons in addition to the 5 large ones already known. It is likely that there are several more tiny satellites within the rings.

Uranus’ magnetic field is odd in that it is not centered on the center of the planet and is tilted almost 60 degrees with respect to the axis of rotation. It is probably generated by motion at relatively shallow depths within Uranus.

Uranus is sometimes just barely visible with the unaided eye on a very clear night; it is fairly easy to spot with binoculars (if you know exactly where to look). A small astronomical telescope will show a small disk. There are several Web sites that show the current position of Uranus (and the other planets) in the sky, but much more detailed charts will be required to actually find it. Such charts can be created with a planetarium program.

Uranus’ Satellites

Uranus has 27 named moons:

  • Unlike the other bodies in the solar system which have names from classical mythology, Uranus’ moons take their names from the writings of Shakespeare and Pope.
  • They form three distinct classes: the 11 small very dark inner ones discovered by Voyager 2, the 5 large ones (right), and the newly discovered much more distant ones.
  • Most have nearly circular orbits in the plane of Uranus’ equator (and hence at a large angle to the plane of the ecliptic); the outer 4 are much more elliptical.
Satellite(000 km)(km)(kg)DiscovererDate
Cordelia5013?Voyager 21986
Ophelia5416?Voyager 21986
Bianca5922?Voyager 21986
Cressida6233?Voyager 21986
Desdemona6329?Voyager 21986
Juliet6442?Voyager 21986
Portia6655?Voyager 21986
Rosalind7027?Voyager 21986
Belinda7534?Voyager 21986
Perdita7640?Voyager 21986
Puck8677?Voyager 21985

Uranus’ Rings

RingDistance (km)Width (km)
Zeta39,6003,500 (formally 1986U2R)
Lambda50,0241-2 (formally 1986 U1R)
Nu67,3003,800 (formally R/2003 U2)
Mu97,70017,000 (formally R/2003 U1)

(distance is from Uranus’ center to the ring’s inner edge)

Interesting Facts about Uranus

  • Uranus is named after the father of the Roman god Saturn. This is most likely due to its similarities with the planet Saturn.
  • Uranus has a diameter of 29297 miles (47,150 kilometres). It is the smallest of the gas giants but still four times bigger than Earth.
  • Uranus is the Seventh planet from the sun. It is 1782 million miles (2869 million kilometres) from the Sun and is between Saturn and Neptune.
  • A day on Uranus is 17 hours and 14 minutes. This is how long it takes to turn on its axis, so it is rotating at a reasonable speed.
  • A year on Uranus is 84 Earth days. This is how long Uranus takes to orbit the sun.
  • A telescope is needed to see Uranus. This means ancient astronomers were unaware of Uranus as they did not have the necessary equipment to see it. The planet was discovered in 1781 by William Herschel using a telescope.
  • Uranus has 27 moons. Five of these are quite big and the rest a lot smaller. The large ones are named Miranda, Ariel, Umbriel, Titania and Oberon. All of the moons are named after the works of William Shakespeare and Alexander Pope.
  • Uranus is one of the planets in a group called the Gas Giants. There are four of these in the solar system, Uranus, Saturn, Jupiter and Neptune. Uranus is the smallest of the four but is still a lot bigger than Earth.
  • Uranus lies on its side as it goes around the sun. Its axis sits at 98 degrees. This means it spins horizontally. Nobody’s sure why this is but the theory is that long ago an Earth-sized planet may have crashed into Uranus and caused the shift.
  • Uranus is surrounded by 13 rings. These were all discovered quite recently so there may be more. Unlike Saturn, scientists are unsure what the rings around Uranus are made from.
  • Uranus has a mass 14 x that of Earth. That makes it the lightest of all the Gas Giants.
  • The atmosphere of Uranus is made up mostly of hydrogen and helium. This is very similar to Saturn and Jupiter.
  • What makes Uranus different is that it also has a good amount of ices made from water, ammonia and methane. Because of this, the planet is sometimes referred to as one of the Ice Giants. (Uranus and Neptune)
  • The methane in the atmosphere absorbs the red colour on the light spectrum. That is why Uranus appears to be a blue/green colour. They are the colours reflected into space.
  • Astronomers watching Uranus noticed that at a certain point when it goes around the sun, it was being pulled further out of its orbit. Scientists thought this must be due to the gravitational pull of another planet. This is what helped them discover Neptune.
  • The only space mission that has made it near Uranus is The Voyager 2. It flew by the planet in 1986 and gave us the first “close up” pictures of Uranus. Scientists also found evidence of what appears to be an ocean of boiling water roughly 497 miles (800 kilometres) underneath the clouds.
  • Uranus is the coldest planet in our Solar System. The minimum surface temperature is -224 degrees Celcius (- 371 degrees Fahrenheit)

More about Uranus and its satellites

Open Issues

  • Why doesn’t Uranus radiate more heat than it receives from the Sun as the other gas planets do? Is its interior cold?
  • Why is its axis so unusually tilted? Was it due to a massive collision?
  • Why do Uranus and Neptune have so much less hydrogen and helium than Jupiter and Saturn? Is it simply because they are smaller? or because they’re farther from the Sun?
  • What will happen to Uranus’s weather as it progresses through its seasons?