Uranus is the seventh planet from the Sun. It is known as an ice giant. It is a large, gaseous planet with a beautiful cyan color, made mostly of water, ammonia, and methane.

Like the other giant planets, Uranus has a ring system, which contains the known 13 inner moons. Further out are the larger five major moons of the planet: Miranda, Ariel, Umbriel, Titania, and Oberon; and orbiting at much greater distance from Uranus are the known nine irregular moons.

Description
Key Facts
History of discovery
Name
How Uranus formed
Orbit and rotation
What's inside Uranus?
Why is Uranus so cold?
Atmosphere
Magnetosphere
Moons and rings
Exploration
Interesting facts about Uranus
Images for kids
See also

Description

Uranus is a fascinating planet in our Solar System, located far out beyond Saturn. It's one of the two "ice giants" (the other being Neptune) because a large part of its inside is made of icy materials like water, ammonia, and methane, even though it's very hot and dense inside!

Uranus is special for a few reasons. One of the most unique things about it is how it spins. Unlike most planets that spin upright like a top, Uranus spins on its side! Imagine Earth spinning while lying down – that's kind of what Uranus does. This unusual tilt means that its poles face the Sun for about 42 Earth years at a time, followed by 42 years of darkness. This creates very extreme seasons!

Key Facts

Type: Ice Giant Planet
Position from Sun: 7th
Color: Cyan (bluish-green)
Main Ingredients: Water, Ammonia, Methane (in a dense, hot state often called "ice")
Diameter: About 4 times the diameter of Earth
Mass: About 14.5 times the mass of Earth
Rotation Period (Day): About 17 hours and 14 minutes (spins backward compared to most planets!)
Orbital Period (Year): About 84 Earth years
Axial Tilt: About 82.23 degrees (spins on its side!)
Minimum Temperature: About -224 °C (-371 °F), making it the coldest planet in the Solar System.
Known Moons: 28
Known Rings: 13
Discovery Date: March 13, 1781
Discovered By: William Herschel
Visited By: Voyager 2 (in 1986)

History of discovery

Even though Uranus is sometimes bright enough to be seen without a telescope, ancient astronomers didn't recognize it as a planet. They probably saw it but thought it was just another star because it's quite dim and moves very slowly across the sky.

The official discovery happened on March 13, 1781. An astronomer named William Herschel was looking at the sky from his garden in Bath, England, using a telescope he built himself. He noticed an object that looked different from the stars – it seemed fuzzy and its position changed over a few nights. At first, he thought it might be a comet.

Herschel shared his discovery with other astronomers. They observed the object more closely and calculated its path. They realized it wasn't following the stretched-out path of a comet, but a nearly circular path much farther out than Saturn. This meant it was a planet, the first one discovered using a telescope! This discovery was a big deal because it doubled the known size of our Solar System.

Name

After the discovery, there was a discussion about what to name the new planet. William Herschel wanted to name it "Georgium Sidus" (George's Star) in honor of King George III, who supported his work. However, astronomers in other countries preferred names that fit with the traditional names of the other planets, which came from Roman and Greek mythology.

Eventually, the name "Uranus" was suggested by astronomer Johann Elert Bode. He thought it made sense to follow the mythological family tree. Saturn was named after the Roman god of agriculture, who was the father of Jupiter (the king of the gods). Bode suggested naming the new planet after the Greek god Uranus (Ouranos), who was the father of Cronus (Saturn in Roman mythology). This name stuck and became the internationally accepted name for the planet by the mid-1800s.

How Uranus formed

Scientists believe that all the planets in our Solar System formed from a giant spinning cloud of gas and dust called the solar nebula. Most of the gas went to form the Sun. The dust and leftover gas clumped together to form the planets.

Jupiter and Saturn grew very large and gathered huge amounts of hydrogen and helium gas, becoming the "gas giants." Uranus and Neptune also grew, but they didn't grab as much gas. Instead, they ended up with more of the icy materials, which is why they are called "ice giants." Scientists think that Uranus and Neptune might have formed closer to the Sun and then moved outward to their current positions billions of years ago.

Orbit and rotation

Uranus takes a very long time to travel around the Sun – about 84 Earth years for one full orbit. Since its discovery in 1781, it has only completed its journey around the Sun a little over three times!

As mentioned before, Uranus has a very unusual spin. Its axis is tilted by more than 82 degrees! This means it's practically rolling around its orbit on its side.

Because of this extreme tilt, the seasons on Uranus are very different from Earth's. When one of its poles is pointed towards the Sun, that pole experiences continuous daylight for about 42 years, while the other pole is in complete darkness. Around the time Uranus reaches the halfway point in its orbit (the equinox), the Sun shines more directly on its equator, and parts of the planet experience something more like a day-night cycle, but still very different from Earth.

What's inside Uranus?

Scientists think Uranus has three main layers:

A small rocky core in the center, made of rock and metal.
A thick icy mantle surrounding the core. This isn't ice like you'd find in a freezer! It's a hot, dense fluid made of water, ammonia, and methane. This layer is sometimes called a "water-ammonia ocean" and is thought to be electrically conductive.
An outer gaseous envelope made mostly of hydrogen and helium, which is what we see as the planet's atmosphere.

The pressure and temperature deep inside Uranus are incredibly high. Scientists even think that under these extreme conditions, the methane molecules might break apart, and the carbon atoms could form diamonds that rain down through the mantle!

Uranus doesn't have a solid surface like Earth. Its atmosphere just gradually gets thicker and thicker until it becomes the liquid-like icy mantle. When scientists talk about the "surface" of Uranus, they usually mean the level in the atmosphere where the pressure is similar to Earth's atmospheric pressure at sea level.

Why is Uranus so cold?

Even though it's an ice giant, one of the biggest mysteries about Uranus is why it's so cold. It actually has the lowest minimum temperature of all the planets in our Solar System. What's strange is that it doesn't seem to give off much heat from its inside, unlike Jupiter, Saturn, and even Neptune (which is similar in size and makeup). Neptune gives off more than twice the heat it gets from the Sun, but Uranus gives off hardly any extra heat.

Scientists have a few ideas about why this is. One idea is that the giant impact that tilted Uranus also caused it to lose most of its original heat. Another idea is that there might be something in Uranus's layers that stops heat from the core from reaching the surface.

Atmosphere

The atmosphere of Uranus is the part we can see and study from far away. It's made up mostly of hydrogen and helium, just like Jupiter and Saturn. But it also has a significant amount of methane. Methane is very good at absorbing red light, so when sunlight hits Uranus's atmosphere, the red light is absorbed, and the blue and green light is reflected back into space. This is what gives Uranus its beautiful cyan color!

The atmosphere has different layers:

Troposphere: The lowest layer, where the temperature gets colder as you go higher. This is where clouds are thought to form, made of water, ammonium hydrosulfide, ammonia, or methane depending on the altitude and temperature.
Stratosphere: Above the troposphere, where the temperature starts to increase again because of sunlight being absorbed by methane and other gases.
Thermosphere/Corona: The outermost layer, which is very hot, even though Uranus is so far from the Sun. Scientists aren't sure exactly why this layer is so hot. This layer also extends very far out into space.

Compared to the stormy atmospheres of Jupiter and Saturn, Uranus's atmosphere often looks quite calm and featureless. When the Voyager 2 spacecraft visited in 1986, it saw very few clouds. However, as Uranus has moved through its long orbit and the viewing angle from Earth has changed, telescopes like the Hubble Space Telescope have seen more clouds and storms appearing, especially as the planet approaches its equinox (when the Sun shines more directly on its equator).

Magnetosphere

Uranus has a magnetic field, but it's very strange! On Earth, our magnetic field is pretty much lined up with our planet's spin axis and comes from the center. Uranus's magnetic field is tilted by a huge 59 degrees from its spin axis, and it doesn't come from the very center of the planet – it's offset!

This creates a very lopsided magnetosphere (the area around a planet controlled by its magnetic field). The magnetic field is much stronger on one side of the planet than the other. Scientists think this unusual magnetic field might be generated in the icy mantle layer, rather than the core like on Earth or the gas giants.

Moons and rings

Uranus has a system of moons and rings orbiting it. As of May 08, 2025, 28 moons are known. The five largest moons are Miranda, Ariel, Umbriel, Titania, and Oberon. These moons are made of a mix of ice and rock. They are much smaller than Earth's Moon. Miranda is particularly interesting because it has a very jumbled-up surface with deep canyons and strange features, suggesting it had a violent past.

Uranus also has a system of rings, although they are much fainter and darker than Saturn's famous rings. There are 13 known rings. They are made of very dark particles, ranging in size from tiny dust grains to small rocks. The rings are quite narrow. Scientists think the rings are relatively young and might have formed from the breakup of a moon or moons that were shattered by impacts.

The rings were first definitely discovered in 1977 when astronomers watched Uranus pass in front of a star. They saw the star blink out several times before and after Uranus itself blocked the star, which meant there were rings around the planet. Voyager 2 later took pictures of the rings. More recently, the Hubble Space Telescope discovered two faint outer rings, one of which shares its orbit with a small moon called Mab.

Exploration

So far, only one spacecraft from Earth has visited Uranus: Voyager 2. It flew by Uranus on January 24, 1986. Voyager 2 took amazing pictures and gathered lots of data about Uranus, its moons, rings, and magnetic field. It discovered new moons and rings and gave us our first close-up look at this distant, sideways planet.

Since Voyager 2, no other missions have been sent to Uranus. However, scientists are very interested in going back to learn more about ice giants.

Interesting facts about Uranus

Uranus is the only planet named after a Greek god, while the others are named after Roman gods.
The planet is visible to the naked eye.
It doesn't have a solid surface like Earth.
Winds in its atmosphere can be very strong, blowing at hundreds of kilometers per hour.
As of 2023, it was visited up close only once when in 1986 the Voyager 2 probe flew by the planet.
Its average distance from the Sun is about 20 times the distance between the Earth and the Sun. This means sunlight is much, much weaker at Uranus than it is here.
Scientists aren't completely sure why Uranus is tilted so much, but the most popular idea is that a very large object, perhaps about the size of Earth, crashed into it billions of years ago and knocked it onto its side.
Uranus's magnetosphere traps charged particles, forming radiation belts. These particles can interact with the planet's atmosphere to create aurorae, similar to the Northern and Southern Lights on Earth.
The chemical element uranium, discovered in 1789 by the German chemist Martin Heinrich Klaproth, was named after the then-newly discovered Uranus.
Operation Uranus was the successful military operation in World War II by the Red Army to take back Stalingrad and marked the turning point in the land war against the Wehrmacht.
In astrology, the planet Uranus (symbol ) is the ruling planet of Aquarius.
Because Uranus is cyan and Uranus is associated with electricity, the colour electric blue, which is close to cyan, is associated with the sign Aquarius.

Images for kids

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Position of Uranus (marked with a cross) on 13 March 1781, the date of its discovery
William Herschel, discoverer of Uranus
Johann Elert Bode, the astronomer who suggested the name Uranus
Simulated Earth view of Uranus from 1986 to 2030, from southern summer solstice in 1986 to equinox in 2007 and northern summer solstice in 2028.
Uranus seen through an amateur telescope, shortly after lunar occultation, during the November 2022 lunar eclipse
Size comparison of Earth and Uranus
Diagram of the interior of Uranus, listing each layer's composition
Diagram of the Uranus atmosphere's composition and layers, along with the graph of its pressure
Uranus's upper atmosphere imaged by HST during the Outer Planet Atmosphere Legacy (OPAL) observing program.
Planet Uranus – North Pole – Cyclone (VLA; October 2021)
Voyager 2's timelapse of Uranus's dynamic atmosphere
The first dark spot observed on Uranus. Image obtained by the HST ACS in 2006.
Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible (HST ACS image).
The magnetic field of Uranus(animated; 25 March 2020)
A diagram showing Uranus's asymmetric magnetosphere
Major moons of Uranus in order of increasing distance (left to right), at their proper relative sizes and albedos. From left to right, they are Miranda, Ariel, Umbriel, Titania, and Oberon. (collage of Voyager 2 photographs)
Uranus as seen from the Cassini spacecraft at Saturn