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Diving Deep Inside Uranus

Let's get the jokes out of the way: In this blog post will be diving deep inside Uranus, Uranus has a dark spot, Uranus has a ring around it, and of course Uranus is a gas giant surrounded by a cloud of methane. Now to ruin this fun most people say yoo-rain-us or more crassly ur-anus when talking about the 7th planet from the sun. I usually say oo-ron-us which is closer to the Greek pronunciation and side steps the giggles. Say it how ever you feel, I just want this article to entertain you and jokes are entertaining.

Uranus’s name comes from Greek mythology just like all of the planets (the Romans renamed them to their gods who were just borrowed from Greek mythology). The Greek names for the planets are: Mercury = Hermes, Venus = Aphrodite, Earth = Gaia, Mars = Ares, Jupiter = Zeus, Saturn = Cronus, Uranus = Uranus, Neptune = Poseidon, Pluto = Hades. There’s a subtle family tree here Hermes, Aphrodite, and Ares are all children of Zeus, Zeus is Cronus’s son, so it would follow that the next planet out would be named after Cronus’s father. Uranus is the god of the sky. The myth is Uranus (the god of the sky) and Gaia (the god of the earth, “mother earth”) are the first primordial gods which everything came from.

Uranus the god of eternity, is standing inside a celestial sphere decorated with zodiac signs, in between a green tree and a bare tree (summer and winter, respectively). Sitting in front of him is the mother-earth goddess, Tellus (the Roman counterpart of Gaia)

Uranus was the first planet to be discovered in a telescope, and with that the first planet to be discovered at all. All of the planets closer to the sun than Uranus are so obvious in the night sky that any one that spends a bit of time outdoors (as our ancestors did) would notice them wandering in the night sky. However Uranus is so far and small you can just barely see it without a telescope.

Uranus was discovered by William Herschel in 1789. William Herschel was a brilliant self-educated astronomer who built his own telescopes because he couldn’t afford one. He ended up so good at this that he built the best telescope around in his time. He made many discoveries including two moons of Saturn, and Mars axis was tilted just like Earth’s.

Friedrich Wilhelm Herschel 1738 - 1822

While studying the stars in Gemini Herschel noticed one that appeared as a disk in his telescope. You see stars are so far away that even the best telescopes can’t see them as more than a point of light. Planets are close enough we see some surface detail. In perspective Uranus would be like looking at a sesame seed from 200 yards away (2 football fields), which can be done with a powerful telescope. Where looking at the closest star (Alpha Cen) would be like looking at a grapefruit 2,000 miles away (about the distance from boulder to Belize) which even the best telescopes can’t do. We see stars as points of light because they are so far but really bright and we see planets as disks because they are close enough to resolve their surface. Herschel was very hesitant to say he discovered a planet. He tried to call it a commit but, it was a well defined circle, not a haze that you would expect from a commit. Even after he had enough observations to see it had a circular orbit (not the round orbit expected of a comet) he hesitated in saying it was a planet. It was actually another astronomer (Anders Jean Lexell) that claimed Herschel had discovered a planet beyond Saturn. Herschel was given the right to name the new planet as the discoverer but he wanted to name it after the British king George III, and called it “Georgium Sidus” of “George's Star”. He obviously knew who would write him the biggest check. I also want to point out he never wanted to call Uranus just “George” I see this in Trivia from time to time, and not in any primary sources. While a planet named George is a funny prospect it would've been disrespectful to call a monarch by their first name. Astronomers outside of the UK disliked naming it after a British monarch and other names were proposed. The most notable of the other names is calling it Herschel after the discoverer. However the tradition of naming planets after Greek gods was given favor and the name Uranus outlasted all of these names. Uranus wasn’t discovered for so long for a few reasons, all mainly having to do with it’s distance from the sun. Uranus is twice as far from the sun as Saturn (it’s discovery doubled the size of our solar system) and half the size of Saturn. This makes Uranus .36% the brightness of Saturn. Saturn is the ninth brightest thing in our sky there’s a few stars (our sun, Sirius, and Canopus), and of course the moon and other planets that are brighter than Saturn. However there’s about 5,000 stars that are brighter than Uranus, it’s easily looked over.

Another thing that sets planets apart is they move among the background stars which stay still (the word planet actually means “wanderer” or wandering star). Uranus is no exception however it is much slower around the sun than the other planets. It takes Uranus 84 years to orbit the sun (meaning for every 84 times earth goes around the sun Uranus goes once), where Saturn takes about 30 years to orbit the sun, Jupiter about 12 years, and mars about 2 years. This means it takes Uranus 44.4 days to move the width of one full moon in our night sky, where Saturn takes 15 days, Jupiter 6.25 days and mars about a day.

Table of apparent motion of Uranus compared to the other outer planets.

Uranus is much slower to move around the zodiac (the zodiac being the only constellations that are visited by planets because, they fall on the “ecliptic”, the line that denotes the plane of our solar system). There are 12 constellations in the zodiac and Uranus takes 84 years to go thru all of them meaning Uranus spends 84/12=7 years in each sign. Because of the infrequency when Uranus transits between constellations Astrologers put more weight into it when this happens. I of course know very little of astrology however for this post I’ve teamed up with my good friend Sarah at Lives Her Vision and she has a blog post here covering the astrological side of Uranus.

The other planets motion is much more noticeable when observing month to month/year to `year than Uranus. Many astronomers saw Uranus before it was discovered and even cataloged it. In the mid 1700's an astronomer (Pierre Charles Lemonnier) recorded Uranus 12 times each time thinking it was a different star.

Uranus has many things that set it apart from the other planets. It is the only planet that rolls on its equator in its orbit rather than spins like a top. To put it a more scientific way Uranus has an axial tilt of 97.77°. If you could stand on the surface of Uranus and see the sky clearly you would see the sun spiral around the sky tracing out almost a helix pattern in the sky, this would happen very slowly and take 84 years to watch unfold completely.

Being so far from the sun means the sun wouldn’t appear nearly as bright in the sky as it does on earth. The sun would be about a 20th the size it appears in our sky and the sun would be 1/368th as bright (still 1,250 times as bright as a full Moon). Because of this Uranus is very cold, it is the coldest planet in our solar system ( Uranus is even colder than the further planet Neptune, for reasons we are not 100% sure of but likely to do with it being tilted on its side).

Uranus is radius is about 4 times that of earth's. It is mostly comprised of hydrogen and helium with frozen water, ammonia and methane present as well. Storms have been observed in the atmosphere of Uranus, the “dark spot on Uranus” I mentioned in the start of this is one such storm just like Jupiter's great red spot. Uranus is very similar in composition to its neighbor Neptune which has given the two the classification of “Ice Giants” to separate them out from Jupiter, and Saturn (the gas giants). Deep beneath Uranus’s thick atmosphere is a core that is thought to be about the size of Earth.

Size comparison

Uranus has 27 known moons all of which are names after characters from the works of Shakespeare, breaking the tradition of giving Greek names to the planetary bodies. The largest moon is Titania, which is about half the size of our moon, it’s the 8th largest moon in the solar system.

Uranus and its six largest moons compared at their proper relative sizes and relative positions. From left to right: Puck, Miranda, Ariel, Umbriel, Titania, and Oberon

Uranus has a ring system as well, it was the first in 1977 when Uranus passed in front of a star. Many astronomers were observing this event and to everyone’s surprise before Uranus covered the star, the star dimmed 5 separate times and after Uranus passed in front of the star 5 more dimming events took place. This could only mean Uranus had at least 5 rings. We’ve only gotten an up close look at Uranus from the Voyager 2 flyby in 1986, in this flyby we learned most of what is known today about the Uranian system. Voyager 2 got to see the rings up close and counted 13 of them.

Rings of Uranus seen by Voyager 2

Observing Uranus is difficult for an amateur astronomer, and when found it offers very little to be seen. A telescope of about 6 inches or larger can resolve a small pale blue disk under a magnification of 85x or greater. But that’s about all there is to see, just that it’s not a point of light like a star. If you are really patient and track it down in a telescope and then proceed to wait a few months/years and do so again you will see how slowly it moves in the night sky. If you want to see Uranus the best way would be to join me on one of my tours. I’d love to show you Uranus in my large telescopes!

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