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The Planet Uranus

The 7th Planet from the Sun


Discovery of Uranus

The planet Uranus (pronounced either ū·rā′·nəs or ūr′·ə·nəs) is visible to the naked eye, and has therefore been watched by mankind for thousands of years. However, because it is so distant from us it moves much more slowly across the sky than the other planets visible from Earth.

As a result, it wasn't identified as a planet until 1781 when Sir William Herschel, using a telescope, discovered that it was, indeed in orbit around our Sun. Curiously, Herschel initially insisted that this newly re-discovered object was in fact a comet. Though when pressed he made illusions to the fact that it may be more similar to objects like Jupiter or Saturn.

Naming the 7th Planet from the Sun

Herschel initially named the new planet Georgium Sidus (literally George's Star, but taken as George's Planet) in honor of Britain's newly minted King George III.

Unsurprising, however, this name was not met with the same warm reception as it had on the Isle of Britain. Therefore other names were suggested, including Herschel, in honor of its discoverer.

Another suggestion was Neptune, which of course ended up getting used later.

The name Uranus was suggested by Johann Elert Bode, which is the Latin translation of the Greek God Ouranos. The thinking went that Saturn was the father of Jupiter, so the next world out when be the father of Saturn: Uranus.

This line of thinking was well received by the international astronomy community, and eventually became the sole name recognized for the planet in 1850.

Orbit and Rotation

Uranus has a not-insignificant eccentricity, giving it a spread in radial distance from the Sun of more than 150 million miles. But on average Uranus is about 1.8 billion miles from the Sun, orbiting the center of our solar system every 84 Earth-years.

The interior of Uranus (that is, the surface area below the atmosphere) rotates every 17 Earth-hours of so, while the atmosphere, with its intense winds makes it around the planet in as little as 14 hours.

The most unique feature of the faint-blue world is the fact that it has a highly tilted orbit. At nearly 98 degrees with respect to the orbital plane, the planet appears to at times "roll" along its orbit.


Determining the structure of planets is a tricky business since we can't just drill deep inside and see what times out. We have to take measurements of what elements are present, typically using techniques such as reflection spectra, then using information such as its size and mass to estimate how much (and in what states) the various elements exist.

While not all models agree on the details, the general consensus is that Uranus has three distinct layers:

  • Rocky Core: With less than 4% of the planet's total mass the rocky core is relatively small.
  • Mantel: At more than 90% of the Uranus's total mass, the mantel makes up the majority of the planet. The primary molecules include water, ammonia and methane (among others) in a semi-ice-liquid state.
  • Atmosphere: Containing the outer 20% of Uranus' radius, the atmosphere contains less than 4% of the planetary mass making it the least dense of the layers. It consists primarily of elemental hydrogen and helium.


Everyone knows about the rings of Saturn, but actually the outer four planets all have rings. Uranus was the second world discovered to have such phenomena.

Like the brilliant rings of Saturn, those around Uranus are tiny individual particles of dark ice and dust. The material in these rings may have one been the building blocks of a nearby moon that was destroyed by impacts from asteroids, or perhaps even by gravitational interactions from the planet itself.

Uranus By the Numbers

  • Equatorial Radius: 25,559 ± 4 km (about 4 Earth Radii)
  • Polar Radius: 24,973 ± 20 km
  • Mass: Approximately 8.6810 × 1025 kg(about 14.5 Earths)
  • Volume: 6.833×1013 km3 (about 63 Earths)
  • Average Distance from the Sun: 1.79 billion miles
  • Surface Gravity (at Equator): 88.6% of Earth's gravity at the equator
  • Rotational Period (length of a day on Uranus): 17 hours, 14 minutes, 24 seconds
  • Orbital Period (length of a year on Uranus): 84.3 Earth Years

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