Uranus

An ice giant, not a gas giant

Uranus is the seventh planet from the Sun and the third largest. It is about four times wider than Earth and holds roughly 14.5 times Earth's mass.

Astronomers call it an ice giant. In planetary science, "ices" means substances like water, ammonia and methane, which here exist as a hot, dense fluid rather than frozen blocks. Jupiter and Saturn are mostly hydrogen and helium, while most of Uranus is this icy fluid wrapped around a small rocky core.

The outer atmosphere is mainly hydrogen and helium with a little methane. Methane absorbs red sunlight and reflects blue and green, which gives Uranus its soft cyan color.

Uranus is also strangely cold inside. Unlike the other giant planets, it gives off very little heat of its own, and its cloud tops sit at about -320°F, among the coldest readings in the planetary system.

A planet lying on its side

Most planets spin roughly upright, like tops. Uranus is tipped by about 98 degrees, so its axis points almost straight along its path around the Sun. In effect, it rolls along its orbit.

The leading idea is that one or more huge collisions early in its history knocked it over. No one has proven this yet, and some researchers think slower gravitational tugs could have done the job instead.

The tilt creates the most extreme seasons of any planet. One Uranian year lasts about 84 Earth years, and for roughly a quarter of that, one pole faces the Sun almost directly. That means about 42 years of continuous daylight at a pole, then about 42 years of night.

Uranus also spins in the opposite direction to most planets. Seen from above Earth's north pole, the Sun would rise in the west there. A day, meaning one full spin, takes about 17 hours and 14 minutes.

Dark rings and literary moons

Uranus has 13 known rings. They are narrow and very dark, made of dust and chunks that reflect little light, so they are hard to see. Astronomers first detected them in 1977, when a background star blinked off and on several times as the rings passed in front of it.

As of 2026, Uranus has 29 known moons. The newest, a small moon only about 6 miles across, was spotted in 2025 in images from the James Webb Space Telescope.

Unlike moons named after Greek and Roman myths elsewhere, Uranus's moons are named after characters from the works of William Shakespeare and Alexander Pope. The five largest are Miranda, Ariel, Umbriel, Titania and Oberon.

Miranda is the oddest of them. Its surface looks patched together, with giant cliffs and grooved terrain, as if it had been broken and reassembled. Titania, the biggest moon, is about 980 miles wide, a little less than half the size of our Moon.

How Uranus was found

Uranus was the first planet discovered with a telescope. On March 13, 1781, the musician and astronomer William Herschel noticed an object in his telescope near the stars of Gemini that looked like a small disk rather than a point. He first thought it might be a comet.

Over the following months, other astronomers worked out its path and showed it was a planet orbiting beyond Saturn. This doubled the known size of the Solar System overnight.

Herschel wanted to name it after King George III. The name that stuck, Uranus, comes from the Greek god of the sky, suggested by the German astronomer Johann Bode.

One visit so far, and plans for more

NASA's Voyager 2 is the only spacecraft to have visited Uranus. It flew past in January 1986, coming within about 50,600 miles of the cloud tops on January 24, 1986. In just a few days it found 11 new moons, two new rings and a strangely tilted magnetic field.

Since then, scientists have studied Uranus from Earth and from space, using the Hubble and James Webb telescopes. These views show bright storms, changing polar caps and seasonal shifts as different parts of the planet come into sunlight.

A 2022 report by the US National Academies ranked a Uranus orbiter and atmospheric probe as the top priority for NASA's next large planetary mission. As of 2026 it is still a proposal, with no confirmed launch date. Because of the long journey, any such probe would take more than a decade to arrive.

The best launch window for such a mission is thought to be the early 2030s, when a flyby of Jupiter could give the spacecraft a gravity boost. If that chance is missed, the journey could take much longer.

How to see Uranus yourself

Uranus sits right at the edge of what the unaided eye can see. Under a truly dark sky, away from city lights, people with good eyesight can sometimes glimpse it as a faint, steady dot, but only if they know exactly where to look.

Binoculars make it much easier. It looks like a slightly greenish star, and it shifts very slowly against the background stars from week to week. A free planetarium app or a monthly star chart will show you its current position.

In a small telescope at around 100x magnification, Uranus shows a tiny, pale blue-green disk with no visible detail. That plain little disk is still worth the effort: you are looking at a world about 1.8 billion miles away, lit by sunlight that left the Sun more than 2.5 hours earlier.

The best time to look is near opposition, when Earth passes between Uranus and the Sun. Then the planet is up all night and at its brightest. This happens about once a year, a few days later each year.