Back To CourseBasics of Astronomy
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Uranus, the second-to-last planet from the sun, is not a very inspiring sight from Earth. Using Earth-based telescopes, it appears as a faint, uninspiring, small, and hazy greenish-blue disk.
We actually don't know much about Uranus. Only one space probe has come close enough to Uranus to gather significant data about it. That was Voyager 2 in January of 1986. Thus, much of our knowledge about Uranus is incomplete and further investigation may cause astronomers to change their opinions about what we know now.
However, this lesson will go over what we do know about Uranus given our best observations so far.
Upon Voyager 2's flyby past Uranus, data confirmed the Uranian atmosphere isn't massively different from Jupiter and Saturn. The Uranian atmosphere is composed of 82.5% hydrogen and 15.2% helium. One distinguishing factor that sets Uranus apart from Saturn and Jupiter is that it contains more methane in its atmosphere.
I tell you this for a reason. The greenish-blue disk I mentioned before? Uranus looks like this because of that 'excess' methane, or CH4, in the atmosphere. Methane absorbs longer wavelengths of light (the reds and yellows). This means that the sunlight that's reflected by Uranus is devoid of red and yellow colors, the colors Saturn and Jupiter clearly have. Thus, Uranus looks more blue-green in color.
And the haze I mentioned in the intro? That's due to the sun's UV light converting some of this methane gas into a hydrocarbon haze, which makes it hard to see much below the upper atmosphere. And this brings me to my next point.
Do you know why Jupiter's atmosphere has these crazy swirling clouds, while Uranus has a very bland and uniform appearance to it? It's because Uranus is colder than Jupiter. The crazy-looking clouds on Jupiter are made up of ammonia, water, and ammonium hydrosulfide.
Uranus is too far away from the sun, it's too cold, and so the stuff that makes up those clouds freezes and precipitates out of the Uranian atmosphere, giving the planet a largely bland appearance. There are some clouds on Uranus, made of methane, but they're nothing to write home about because they form in the lower reaches of the atmosphere, the ones that are 'hazed out' due to the hydrocarbon, and so they're hard for us to see.
Now that you're a pro about the Uranian atmosphere, let's talk about its layers. At the center of the image on your screen is a core made of heavy elements. The core is then surrounded by a mantle of ammonia and liquid water that's really compressed. Basically, the core is surrounded by a huge amount of window cleaning fluid. Can you imagine the smell of that? That's disgusting. Around this layer, the mantle layer, is another layer that's made of liquid hydrogen, helium, and methane.
And while learning all of that was boring, I'll give you a pretty cool fact about Uranus: Uranus rotates on its side. Meaning, its equator has an incline of about 98 degrees to its orbit. The reason this is actually interesting is because, as a result, half of the planet will be in complete darkness and the other half will always be lit up during its 21-year-long summer and winter seasons. Talk about insomnia!
Another cool thing to learn about Uranus? The IAU, or the International Astronomical Union, the organization deciding how to name stuff out in space, has said that Uranus' moons should be named after the characters in the plays of William Shakespeare and Alexander Pope. Uranus has 27 moons, by the way, with names like Oberon, Ariel, and Miranda.
Finally, like the famous Saturn, Uranus does have rings. However, they're not as easily seen from Earth as Saturn's. These rings were discovered thanks to something known as occultation. This is the passage of a celestial object directly in front of another. So, when Uranus passed in front of a star, its rings blocked the star's light temporarily and gave the rings away!
Just imagine this. Go and place a hula hoop around your waist. Have another friend turn on a flashlight that's facing a white wall. That'll be our star. If you, Uranus, pass directly in front of the flashlight (the star), you'll block the light. But as you keep moving, you'll see the hoop (the rings) also casts a shadow as it blocks the light. That's occultation, and that's how the rings were discovered.
However, the majority of our knowledge about the rings came from, once again, Voyager 2's flight past the planet. We know that the dark rings are made of water ice mixed with methane. As with Jupiter and Saturn, the rings formed from and are periodically resupplied by material that is ejected from impacts on the planet's moons by other celestial objects, like comets.
Uranus is the second-to-last planet from the sun. Its atmosphere is composed of hydrogen, helium, and methane, or CH4. The latter is responsible for planet's color. The planet is made of a core of heavy elements, surrounded by a mantle of water and ammonia, which is in turn surrounded by a layer of liquid hydrogen, helium, and methane.
Uranus has 27 moons, named for characters in Shakespeare's and Pope's plays, as set by the IAU, International Astronomical Union. Uranus also has rings, discovered thanks to occultation, the passage of a celestial object directly in front of another.
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Back To CourseBasics of Astronomy
28 chapters | 325 lessons