The Idiot’s Guide to Everything: Uranus

Posted on December 7, 2011

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URANUS

As we continue our journey through the outer reaches of our solar system, we reach the seventh planet from the sun, Uranus. The 3rd biggest planet by radius and the 4th biggest by mass, Uranus is named after the Greek deity of the sky, the father of Kronos and the grandfather of Zeus. It is visible to the naked eye occasionally, but because of its dimness and slow orbit it was never considered to be a planet. Uranus is placed in one of two categories by astronomers. It is either the 3rd of the gas giants, along with Jupiter or Saturn, or more frequently now it is referred to as the 1st of the ice giants, along with its twin, Neptune. This is because despite having an atmosphere that is full of hydrogen and helium, it also has traces of ices such as water, ammonia and methane. These are called ices because they solidify at cold temperatures. The amount of methane in the atmosphere also gives Uranus its bluey-green colour. And to dispel any hilarity and years and years of terrible jokes, it is actually pronounced ‘yurah-nus’, with emphasis on the ‘yu’.

Uranus has the coldest planetary atmosphere in all of the solar system, with minimum temperatures of -224 degrees Celsius. It has a complex layered cloud structure, with the lowest clouds full of water and the upper clouds full of methane. It has an interior made of ice and rock. Because of the high levels of methane, Uranus is a practically featureless planet. This is not to say it is dead however, and the winds on the planet can reach up to 560 miles per hour. Uranus seems featureless as because it is so cold, its clouds reside deep in the atmosphere. Because of its rapid winds, a day on Uranus lasts longer in the interior (17 hours) than it does on the visible surface (14 hours). As with Saturn, these incredible wind speeds cause Uranus to bulge out at its equator. This does not lead it to look like a ball however, as there is something that sets Uranus apart from all the other planets. It has a completely unique axis of rotation, and is tilted sideways. This means that its poles actually lie where our equator is. It is believed that this is because of a giant impact the past, which would have knocked it onto its side. Like all of the giant planets in the outer reaches of our solar system, Uranus has its own complex ring system, made up of 13 thin and widely separated rings. 2 of these rings are much further away than the others. The brightest ring is known as the Epsilon ring. The Epsilon ring is around 60 miles wide and has two of its own shepherd moons, Cordelia and Ophelia.

Uranus is also unique in the solar system because of the system used to name it and its 27 satellites. It is the only planet with a name that is derived from Greek mythology as opposed to Roman, Not only this, but all of its named moons received their names from the works of Shakespeare. Of these 27 satellites there are 5 classic ones, of which Titania is the biggest. Similar to many other moons, it has an icy crust, craters, large cliffs and valleys. Another moon, Oberon, has a brown surface of ice and rock, and it also has dark patches that could be layers of organic slush. The other 3 classical Uranian satellites are Umbriel, Ariel and Miranda, a potato shaped ice world with extremely unusual terrain. Uranus has a mass of 14 times that of Earth, which makes it the least massive of all of the giants. It is also the 2nd least dense planet, after the floating Saturn. A year on Uranus lasts all of 83.7 Earth years, which leads us to the real area of interest surrounding this icy giant. 83.7 Earth years is also the length of time that its discoverer, sir William Herschel, lived.

The discovery of Uranus, and subsequent discovery of Neptune, cannot be underestimated with regards to modern astronomy. When it was discovered by William Herschel in March 1781, it became the first planet to be discovered in the modern age, the first that was discovered by telescope and the first expanding of the solar borders since pre-history. The funny thing is however, that Herschel was not even looking for a planet in the first place. He was tracking comets, and indeed he first considered that the body we now know as Uranus could be a comet. The earliest recorded sighting of Uranus is in fact by John Flamsteed in 1690, but he, like many others, mistook it for a star. After intense studying, it became apparent to Herschel that what he was observing was not a comet, but in actual fact a planet, all be it one with an extremely bizarre orbit.

Once the discovery was confirmed, the hard task of naming the planet began. The immediate idea was to name the planet after its finder, Herschel, but this idea was immediately put down by William Herschel. Given the option of naming the planet himself, Herschel decided on calling it ‘Georgium Sidius’ (George’s Star), after the British king at the time. Understandably, this caused all levels of outrage and disapproval internationally, and for a long time after its discovery there were in fact 3 names for the planet, these being Uranus in most of Europe, Herschel in France and the Georgian in England. Neptune was also considered as the name for this icy beast. As the need for an internationally recognised name grew, it was settled that the planet would be called Uranus, to keep in line with the previously used system. (Saturn was named after the father of Jupiter, so Uranus was named after the father of Saturn). At this time, Herschel also discovered 2 of Uranus’ moons, and decided to name them after Shakespearean characters, a trend that sticks to this day.

As mentioned, the discovery of Uranus as a planet was extremely difficult due to its strange orbit. There began to be theories that the reason for this orbit was that there was another planet out there that was influencing Uranus, that was pulling it out of position. Indeed, Urbain le Verrier, a French mathematician, was able to calculate the position of this phantom planet, and the search for it began. But more on that next time. Uranus is an important sign post in the history of our solar system, and one that should not be ignored. A green world of high winds and truly bizarre characteristics, it signals the birth of astronomy in the modern age.

 

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