Meet the Solar System: Uranus

How well do you know your astronomical neighborhood? Let's go on a trip through our solar system and explore the weird, the wild, and the beautiful all around us. Today, we are learning all about Uranus.

Where is it?

Uranus is the seventh planet of our solar system, sitting 1.78 billion miles from the sun and 1.75 billion miles from Earth. From this distance, it takes sunlight 2 hours and 40 minutes to travel from the Sun to Uranus.

Who “discovered” it?

Uranus was the first planet found with the aid of a telescope. It was discovered in 1781 by astronomer William Herschel, although he originally thought it was either a comet or a star. Surprised it wasn’t our good friend Galileo? We are too. But, the distance to the planet made it much harder to see without aid of more sophisticated lenses.

It was two years after Herschel’s observation that the object was universally accepted as a new planet, in part because of observations by astronomer Johann Elert Bode. Rather than using advanced telescopes to more definitively mark Uranus as a planet, Bode’s contribution was one of research.

The German astronomer consulted older records and determined the object Herschel had found had been observed in old sky charts. Between 1690 and 1769, French astronomer Pierre Charles Le Monnier and English astronomer John Flamsteed observed what they thought was a star.

1785 portrait of William Herschel by Lemuel Francis Abbott

The reason they had mistaken it was that Uranus takes a glacial pace in orbiting the Sun. We will get into the details more later in this article, but Uranis takes about 84 years to make one orbit of the Sun. No wonder individual astronomers assumed it was as stationary as other stars.

What’s up with the name?

I know, this section usually comes before “Who discovered it?” but since Uranus was found relatively recently compared to the other planets in our solar system, the people who discovered it played a part in naming it.

Herschel tried unsuccessfully to name his discovery Georgium Sidus after King George III. Instead, the scientific community accepted Bode's suggestion to name it Uranus, the Greek god of the sky, as suggested by Bode.

You also read that right. Uranus is the first non-Earth planet to be named after a Greek god, not its Roman counterpart. He is also one of the founding deities in the Greek pantheon. His family with Gaia beget the Titans, which included Cronus, or Saturn, who we recently discussed. That makes him the grandfather of Zeus, or Jupiter.

The radioactive element uranium was named after Uranus when it was discovered in 1789, just eight years after the planet was discovered.

What’s it made of?

Uranus is another gas giant, possessing the third-largest diameter of any planet in the solar system. With a radius of 15,759.2 miles (25,362 kilometers), Uranus is four times wider than Earth. If Earth was the size of a nickel, Uranus would be about as big as a softball.

Uranus is one of two ice giants in the outer solar system (the other is Neptune). Most (80% or more) of the planet's mass is made up of a hot dense fluid of "icy" materials – water, methane, and ammonia – above a small rocky core. Near the core, it heats up to 9,000 degrees Fahrenheit (4,982 degrees Celsius).

Uranus is slightly larger in diameter than its neighbor Neptune, yet smaller in mass. It is the second least dense planet; Saturn is the least dense of all.

Uranus gets its blue-green color from methane gas in the atmosphere. Sunlight passes through the atmosphere and is reflected back out by Uranus' cloud tops. Methane gas absorbs the red portion of the light, resulting in a blue-green color.

While not as striking in appearance as Saturn, Uranus does have two sets of rings. The inner system of nine rings consists mostly of narrow, dark grey rings. There are two outer rings: the innermost one is reddish like dusty rings elsewhere in the solar system, and the outer ring is blue like Saturn's E ring.

Can we live there?

In short, no.

As an ice giant, Uranus doesn’t have a true surface. The planet is mostly swirling fluids. While a spacecraft would have nowhere to land on Uranus, it wouldn’t be able to fly through its atmosphere unscathed either. The extreme pressures and temperatures would destroy a metal spacecraft.

Think about how long it takes sunlight to reach Uranus. That means any warmth from the Sun is long extinguished as its rays journey to the ice giant. Hence the ice.

Uranus' planetary atmosphere, with a minimum temperature of 49K (-224.2 degrees Celsius) makes it even colder than Neptune in some places. Wind speeds can reach up to 560 miles per hour (900 kilometers per hour) on Uranus, which also would prevent survival on the surface.

How long is a year there? What about a day?

One day on Uranus takes about 17 hours (the time it takes for Uranus to rotate or spin once). And Uranus makes a complete orbit around the Sun (a year in Uranian time) in about 84 Earth years (30,687 Earth days).

Uranus is the only planet whose equator is nearly at a right angle to its orbit, with a tilt of 97.77 degrees – possibly the result of a collision with an Earth-sized object long ago. This unique tilt causes the most extreme seasons in the solar system. For nearly a quarter of each Uranian year, the Sun shines directly over each pole, plunging the other half of the planet into a 21-year-long, dark winter.

Uranus is also one of just two planets that rotate in the opposite direction than most of the planets (Venus is the other one), from east to west.

Has NASA sent any missions there?

Voyager 2 is the only spacecraft to fly by Uranus. No spacecraft has orbited this distant planet to study it at length and up close. Voyager 2 launched on August 20, 1977, from Cape Canaveral, Florida aboard a Titan-Centaur rocket. Voyager 1 launched two weeks later, also from Florida, meaning Voyager 2 was actually first into orbit.

At its closest, the spacecraft came within 81,500 kilometers (50,600 miles) of Uranus's cloudtops on Jan. 24, 1986.

Voyager 2 radioed thousands of images and voluminous amounts of other scientific data on the planet, its moons, rings, atmosphere, interior and the magnetic environment surrounding Uranus.

This archival photo shows engineers working on NASA's Voyager 2 spacecraft on March 23, 1977.

Voyager 2's images of the five largest moons around Uranus revealed complex surfaces indicative of varying geologic pasts. The cameras also detected 11 previously unseen moons.

Several instruments studied the ring system, uncovering the fine detail of the previously known rings and two newly detected rings. Voyager data showed that the planet's rate of rotation is 17 hours, 14 minutes.

The spacecraft also found a Uranian magnetic field that is both large and unusual. In addition, the temperature of the equatorial region, which receives less sunlight over a Uranian year, is nevertheless about the same as that at the poles.

Can I see it from here?

Uranus is not visible to the naked eye, but can be seen with high-powered telescopes.

Are there any pretty pictures of it?

Of course! There are many amazing shots of Uranus, though maybe not as many as some of the other planets that have seen more exploratory missions. Here are our favorites.

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