Lesson Seven

Uranus

Uranus was discovered by telescope in 1781 by William Herschel. It was named for the Greek Titan god of the sky, and is classified as both an Ice Giant and a Gas Giant. Uranus’s axis of rotation lies almost 90 degrees off to one side, which makes it almost "tipped over". Uranus's north pole completes one full circuit every 17.2 hours, and one full year in 84 Earth years. Over time, Uranus has gradually moved along it's orbit and further away from the sun. The nights grew longer each day until. 21 Earth years after the summer solstice, the autumnal equinox would occur, with day and night each at 8.5 hours long.

Atmosphere: This planet's atmosphere is much like Saturn and Jupiter, with the majority being hydrogen, then helium and methane. Ammonia is not present is any significant quantities. As the methane concentrates, it makes Uranus appear bluish green (which is why Neptune appears so blue). The clouds on Uranus are much like cirrus clouds on Earth, made of mostly ice crystals and formed in the planet's cold upper atmosphere. The planet also lacks any internal heat, and Uranus has a very low surface temperature. 

Moons: 27 moons are known to orbit Uranus today. Also discovered by William Herschel is Titania and Oberon, two of the planet's five largest moons in 1789. In 1851 William Lassel found Ariel and Umbriel, the next-largest moons, and Gerard Kuiper found the smallest moon, Miranda, in 1948, which has ten moons of its owns. Many of the moons’ names came from characters from William Shakespeare’s plays and some of Alexander Pope’s more famous works. 

Rings: Like other Jovian planets, Uranus has rings. There are a total of nine thin rings around Uranus. The main rings, in order of increasing size, are named Alpha, Beta, Gamma, Delta and Epsilon, and they range from 44,000 to 51,000 kilometers from the direct centre of the planet. They are quite different to Saturn's. They are dark, narrow and widely spaced unlike Saturn's bright wide, and tightly spaced ones. Both sets of rings are made of particles ranging in size, from dust grains to large boulders

To read: Chapter Eleven of textbook