Lissa graduated from NC State University with a Bachelor's Degree in geology in 2015. Learning and writing about science is her passion.
What's Up With Uranus?
Have you ever looked at a chart of the solar system and wondered "What's up with that one towards the end that's flipped over on its side? And why is it that pretty blue-ish green color? ...And what's with the name?". Well, like a doctor, I am here to answer all of your burning questions about Uranus. Let's start with how the world first noticed Uranus.
How Was Uranus Discovered?
Uranus is the 7th planet of our solar system, discovered by William Herschel in 1781, 171 years after Galileo first spied the rings of Saturn, the next closest planet. Even though Galileo would use a telescope later in his astronomy career, he was able to see Saturn without one because it shone so brightly. Uranus is actually the first planet to be discovered with a telescope, paving the way for the discovery of hundreds of thousands of planets in different solar systems with the Hubble Space Telescope.
Funnily enough, Herschel's discovery was made completely by accident. The amateur astronomer, an immigrant from Germany to England who played various gigs as an organist, was sitting in his garden fiddling with a handmade telescope when he noticed a dim orb floating in front of some stars that weren't moving. This told him that the strange object was closer than the stars, and this piqued his curiosity.
At first, he thought it was a comet, but as he made more observations he realized it didn't have a tail. He reported his findings to the royal astronomy society, who joined him in observing the body that Herschel wanted to name "Georgium sidus," after King George III. The other astronomers calculated that the movements of Uranus were likely planetary, making Uranus, and William Herschel, famous.
In some countries that disliked England, such as France, the planet was nicknamed Herschel, like its creator, until the final name was adopted. However, the king of England was so flattered that he appointed Herschel as his personal astronomer, allowing the former musician to pursue a lucrative career as a telescope manufacturer and 16th-century celebrity.
So... Why Did They Name It Uranus?
Uranus was ultimately named by Johann Elert Bode, a German astronomer. He wanted the planet to fit in with the others that were named after the Greek/Roman pantheon, and found Ouranus, the primordial father of the sky, to be a perfect choice. Interestingly Ouranus is the Greek name for him; if they were to choose the Roman option like the other planets, we would be talking about the planet Caelus right now. Also, Ouranus is the father of Cronus, known to the Romans as Saturn.
To make it a little easier to pronounce, astronomers dropped the "O," meaning for it to be pronounced as "your-a-nuss." However, people nowadays tend to pronounce it differently, particularly in America.
Benjamin Franklin (founding father, lover of science and double entendres) was known to be in frequent correspondence with Bode, and he supported naming the planet after an ancient god rather than a mortal man, and furthermore emphatically supported the Greek name over the Roman because the planet named after "your highness, King George III" was now named "your anus."
Since Benjamin Franklin was basically in every discipline of the political and scientific communities at the time, Franklin's pronunciation stuck, to the delight of jokesters everywhere.
What Is Uranus Made of, and Why Is It Called an Ice Giant?
Uranus is one of our solar system's ice giants, large and cold planets mainly composed of frozen gases with an icy mantle and a small rocky core inside. Uranus's atmosphere is mostly made up of ice, hydrogen and helium gases, and ammonia, but it also contains 2.3% methane, which sits in the upper atmosphere and gives the planet that pale blue-green color.
The planet gets icier and less gaseous the further into its atmosphere you go, and the average temperature of the planet goes from -353 degrees Fahrenheit (-224 Celsius or 49 Kelvin) at the top of its clouds to -371 degrees Fahrenheit in the lower atmosphere, making Uranus the coldest planet in our solar system.
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Deep inside the planet, the pressure is very high. The methane in this area gets broken up, causing the carbon atoms in the methane to crystallize into diamonds that rain down onto the mantle. Uranus's mantle itself is made of liquid metallic carbon, with large iceberg-like diamonds floating on the surface. Uranus's rocky core is composed of iron and nickel, with trace amounts of the components of the layers above.
Uranus's core is unusually cool for a planet's core, at 5000 Kelvin. For comparison, Jupiter's core is 6 times as hot as the core of Uranus. Some scientists think that Uranus's rocky core is so cold because the planet is tipped on its side. The theory is that something large, perhaps another planet, crashed into it when the solar system was forming.
This collision damaged Uranus's core and flipped the whole planet over, so its axis is tilted 98 degrees and it rotates vertically as it orbits the sun, spinning in a way that gives off more heat and energy than it would if the axis were vertical. This frantic vertical rotation also means that Uranus is extremely windy, with its clouds reaching speeds of 360 miles per hour (579 km per hour).
Since the planet is so cold, it glows very dimly compared to other planets, so it went undiscovered for a long time. Because of the extreme cold and wind, as well as having nothing to land on, Uranus would not be able to support life as we know it.
Size-wise, Uranus is a very large planet. 63 Earths can fit inside the volume of Uranus, and its circumference is 99018 miles around (159,354.1 km), about 5 times the circumference of Earth. It has the third-largest diameter in the solar system, at 31693 miles (51005 km), and is the fourth heaviest planet by mass, at 1.914 x 1026 lbs (8.681 x 1025 kg). It weighs 14 times as much as Earth, and it's 4 times as wide as Earth!
Interestingly, Uranus is not a perfect sphere. Since it rotates so rapidly around its axis in a direction opposite to its orbit around the sun, the planet bulges slightly around the center and is slightly squashed at the poles.
Uranus Time Is Nothing Like Earth Time
A day on Uranus lasts 17 hours, 14 minutes, and 24 seconds because it rotates faster than Earth. However, a year for Uranus is 84 years for Earth because of Uranus's longer path around the sun (the planet is 1.8 billion miles or 2.8 billion kilometers from the sun). One year for Uranus consists of 42,718 days.
The extreme 98-degree tilt of its axis means that Uranus's year can be split into a day and night cycle during its solstice (the position where the sun is furthest north or south from the equator), with 21 years of daytime at the north pole in summer and 21 years of nighttime at the north pole in winter.
During its equinox periods (aka springtime and autumn), the time when the sun is closest to the equator, Uranus gets closer to the normal day and night cycle of other planets. The sun doesn't move very much in the sky during these periods. In autumn at the north pole, the sun rises and sets in the west, and in spring at the north pole, the sun rises and sets in the east.
Uranus's extreme seasons lead to extreme changes in weather. The Great Dark Spot that showed up in 2006 appeared as the planet was in springtime, and has grown as the planet approaches summer for the northern hemisphere. The planet will experience its next solstice in 2028, so scientists are curious to see if that's when it grows to its largest point.
The changes in cloud thickness and brightness give Uranus a mottled marble surface during solstice periods and make it look uniform in color during the spring and autumn equinox, which is about when Voyager II flew by to take pictures in 1986.
What's So Odd About Uranus's Magnetic Field?
Even though the axis of Uranus is at 98 degrees, the magnetic poles are tilted at 59 degrees from its rotational axis, so your compass wouldn't point exactly north; instead it would point to some random point on the north end of the planet and wobble around.
The magnetic field is also much stronger on the north side of the planet (4 times the strength of Earth's magnetic field) than it is on the south side (1/3 of Earth's magnetic field), and it doesn't go through the center of the planet, instead shifting to one side.
Instead of enclosing the entire planet, Uranus's magnetic field opens and shuts daily, and its orientation cartwheels around with the planet's rotation, so the planet's protection from solar winds gets switched on and off. The anomalies in Uranus's magnetic field are thought by some scientists to be caused by salt inside the slushy liquid parts of Uranus moving around.
Most planets have their magnetic field created at the core but Uranus's goes through the liquid layer of its atmosphere and skips the core entirely. Uranus has an aurora phenomenon just like Earth, but the auroras are very intense, carrying powerful amounts of radiation, and flicker like a strobe light due to the opening and closing of the magnetic field.
How Many Rings and Moons Does Uranus Have?
Uranus has quite a few things orbiting it, including 13 rings and 27 moons.
The rings of Uranus consist of 9 narrow main rings on the inside, a big red dusty ring, two more narrow faint rings, and a strange blue outer ring. The main rings of Uranus have larger particles than the rings of Saturn, and do not shine quite as brightly. The red ring is composed of iron dust and larger pieces of debris, and orbits between Rosalind and Portia.
The blue ring is composed of tiny submicron-sized particles, following the orbit of the moon Mab, which may have absorbed the larger particles. Instead of being captured by Mab's orbit, there is some kind of force pushing the smaller particles away from the moon. It is unknown where this force is coming from since Mab is too small to be tectonically or magnetically active, only 15 miles in diameter.
The moons of Uranus take their names from the works of Shakespeare and Alexander Pope, unlike the moons of other planets which get their names from mythology. This reflects the fact that Uranus is our first modern-era planetary discovery, and honors Shakespeare and Pope as truly universal writers. There are 5 major moons, and 22 minor moons. Here are the major moons:
- Oberon is the outermost of the major moons, and is probably the oldest. It has a lot of craters, suggesting past volcanic activity, but they are long dead. An unidentified dark material rests on the floor of these craters, and scientists are eager to find out what it is.
- Umbriel is the darkest of the major moons, but it has a mysterious bright ring on one side. This ring may be made of frost deposits circling an impact crater.
- Titania, named after Shakespeare's fairy queen, is the largest of Uranus's moons and the first to be seen by William Herschel in 1787. It has water ice in the surface.
- Ariel has the brightest and youngest surface of all of the moons of Uranus. I has had some recent low-impact collisions that removed some of its bigger craters. It has many valleys and craters reminiscent of our own moon.
- Miranda is the innermost and smallest of the five major moons, and has a strange patchwork surface with fault canyons that are 12 times deeper than the grand canyon in some areas, neatly terraced hills in other areas, and in other areas the surface is fairly flat and pitted with small new craters. Most of the moon is made of ice.
The minor moons are Cordelia and Ophelia, a pair whose gravity holds Uranus's epsilon ring together, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Cupid, Belinda, Perdita, Puck, Mab, Francisco, Caliban, Stephano, Trinculo, Sycorax, Margaret, Prospero, Setebos, and Ferdinand. From Cordelia to Mab are the inner moons, and from Francisco to Ferdinand are the outer moons.
The small inner moons are all intertwined with the rings and orbit closely near each other, jostling for space in a chaotic and unstable arrangement. Cressida may end up crashing into Desdemona or Juliet in the next 100 million years.
The outer moons orbit past Oberon, and are likely to be captured objects sucked into Uranus's gravity while the planet was young. They are all small, basically asteroids ranging from 20 km across to 200 km, and they all orbit the planet irregularly. Margaret is unusual because it orbits in the opposite direction from all the other outer moons, prograde instead of retrograde, following the direction of Uranus's spin.
The Solar System's Most Unique Planet
So now you know more about Uranus, the solar system's most unique planet. The beauty and mystery of this unusual planet has fascinated scientists and artists for centuries, and we will continue to uncover its secrets in the centuries to come. I leave you with Gustav Holst's Uranus, the Magician, a musical composition in his planets series, to appreciate Uranus's place in our culture.
Gustav Holst's "Uranus, the Magician"
- William Herschel - Wikipedia
A biographer of William Herschel, the astronomer who discovered Uranus,
- Who Discovered Uranus (and How Do You Pronounce It)? | Space
Astronomer William Herschel discovered the seventh planet in 1781, but his choice for a name was rejected. Instead, Uranus was destined to cause snickers whenever someone says its name.
- In Depth | Uranus – NASA Solar System Exploration
An overview of the physical characteristics of Uranus by NASA.
- Seasons of Uranus, a sideways world| EarthSky
The seasons of Uranus, each over two decades long, result from its tilted rotation axis, making for strange summers and winters on that planet.
- Dark Spot on Uranus - Scientific American
Witness the first confirmed sighting of a dark spot on Uranus. Long hinted at, astronomers have finally observed a giant vortex, roughly 1,100 miles by 1,900 miles in area--two-thirds the size of the United States.
- Magnetic Field Around Uranus Are a Chaotic Mess | Smart News | Smithsonian Magazine
Using data from the Voyager 2 mission, researchers have modeled Uranus's off-kilter magnetosphere and found an unusual phenomenon.
- Overview | Uranus Moons – NASA Solar System Exploration
An overview by NASA of Uranus's moons.
- Rings of Uranus
The rings of Uranus are intermediate in complexity between the more extensive set around Saturn and the simpler systems around Jupiter and Neptune. The rings of Uranus were discovered on March 10, 1977, by James L. Elliot...
- Planet Uranus Has Rare Blue Ring | Space
The outermost ring of Uranus is bright blue and composed of tiny dust particles, but researchers aren't sure how it got there.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2021 Lissa Clason