Category: Guide to Space

We understand the weather on Earth. The Sun heats the air at the equator, causing it to rise. The warm air goes to the poles, cools down and sinks, and then circulates back. Scientists call this Hadley Circulation. The weather on Uranus works very differently. This is because Uranus is tilted over onto its side, rotating at an angle of 99-degrees.

Over the course of its 84-year orbit, the north pole of Uranus is facing towards the Sun, and the south pole is in total darkness. And then the situation reverses for the rest of the planet’s journey around the Sun. Instead of heating the clouds at the equator, the Sun heats up one pole, and then the other. You would expect the pole facing the Sun to warm up, and to have air currents move towards the other pole.

But this isn’t what happens. The weather on Uranus follows an identical pattern to what we see on Jupiter and Saturn. The weather systems are broken up into bands that rotate around the planet. While Uranus has a completely different tilt from Jupiter and Saturn, it does have internal heat rising up from within. It appears that this internal heat plays a much bigger role in creating the planet’s weather system than the heat from the Sun.

Although less than Jupiter and Saturn, the wind speeds on Uranus can reach 900 km/hour, and seem to be changing as the planet approaches its equinox – when the rings are seen edge on.

We have written many articles about the weather on Uranus for Universe Today. Here’s one that talks about how stormy the planet can get. And here’s one about the discovery of a dark spot in the clouds on Uranus.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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The orbit of Uranus takes 84.3 year to complete one revolution around the Sun. In other words, 1 Uranian year is 84.3 Earth years.

Like the rest of the planets in the Solar System, Uranus doesn’t have a perfectly circular orbit. Instead, it follows an elliptical path around the Sun. Astronomers call a planet’s closest approach to the Sun perihelion. The perihelion for Uranus is 2.75 billion km, or 18.4 astronomical units (1 AU is the distance from the Earth to the Sun). The most distant point of orbit is called aphelion. The aphelion of Uranus is 3.00 billion km, or 20 astronomical units. On average, Uranus orbits at a distance of 2.88 billion km, or 19.2 AU.

Uranus is unique among the planets in the Solar System because of its axial tilt. While Earth is tilted at a mere 23.5 degrees, Uranus has rolled over completely sideways, with an axial tilt of 99-degrees. This has a significant impact on the planet’s seasons. The north pole of Uranus experiences 42 years of complete darkness, followed by 42 years of sunlight, where the Sun never dips below in the horizon. Astronomers aren’t sure why Uranus is flipped over sideways, but they think an impact from a protoplanet early in its history gave it the momentum it needed to roll over.

We’ve written many articles about Uranus for Universe Today. Here’s an article about how we got to see the planet’s rings edge on, and another about how the atmosphere of Uranus can be more violent than previously believed.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

So far, only one spacecraft has ever captured an image of Uranus: NASA’s Voyager 2 spacecraft. So let’s take a look at some pictures of Uranus, some captured by Voyager 2, and others seen from Hubble, and even here on the ground.

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This is the classic image of Uranus, taken by NASA’s Voyager 2 spacecraft during its 1986 flyby of Uranus. During this mission, Voyager 2 came within 81,500 kilometers of the cloudtops of Uranus. Until then, the best pictures of Uranus came from telescopes on Earth. Nothing compared to the pictures of Uranus sent back by Voyager 2.

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This beautiful picture of Uranus might look like it was captured by a space telescope, but it was actually taken from the powerful Keck telescope located on Hawaii’s Mauna Kea. This image shows Uranus in the infrared spectrum, which reveals the detailed cloud patterns in the atmosphere of the planet.

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This Uranus pic was captured by the Hubble Space Telescope. On the left is the image itself, and then on the right are the names of all the moons captured in this photograph of Uranus.

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This beautiful image of Uranus was captured by NASA’s Voyager 2 spacecraft curing its 1986 flyby of the planet. It was actually three images captured at different wavelengths and then combined on computer.

Like these pictures of Uranus? Here are some images of Pluto, and photographs of the Sun.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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The mass of Uranus is 8.68 x 10²⁵ kg.

Want to put that in perspective? That’s 14.536 times more than the mass of Earth. That makes Uranus a pretty massive world, but it’s actually just a tiny fraction of Jupiter. Jupiter is 21.9 times more massive than Uranus.

Even though Uranus is much more massive than Earth, it has a fairly low density. in fact, it’s the second lowest density in the Solar System; only 1.27 g/cm³. If you could stand on the surface of Uranus (you can’t… don’t try), would experience only 89% the force of gravity that you would experience on Earth.

If you could peer inside Uranus, you would discover that most of the planet consists of ices, like water, ammonia and methane.

Here’s an interesting article about the mass of Mercury. And here’s an article about the mass of Jupiter.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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The Earth’s axis is tilted about 23.5 degrees. This is why we have seasons on Earth. But the axis of Uranus is tilted so far it’s hard to imagine how it might have even happened. The axis of Uranus is tilted at an angle of 98-degrees compared to the Sun’s orbital plane.

While the rest of the planets in the Solar System can be thought of like spinning tops, Uranus is more like a rolling ball going around the Sun. During the point of the Uranian solstices, one pole faces the Sun continuously, while the other pole faces away. Only a thin strip of the surface of Uranus experiences any kind of night/day cycle. Uranus’ poles experience 42 years of continuous sunlight, and then 42 years of continuous darkness. During the time of the equinox on Uranus, the planet’s equator is facing the Sun, and so it experiences day/night cycles like we have here on Earth.

What could have caused Uranus to be tilted over on its side like this? Astronomers think that a large protoplanet smashed into Uranus billions of years ago. This collision set the planet tumbling. Eventually it settles into its current axial tilt.

Here’s a cool article on Universe Today about mysteries of the Solar System, including the question, why is Uranus tilted? And here’s an article about images of Uranus and Neptune captured by Hubble.

Here’s the same question posed to “ask a scientist”, and here’s an article from the Planetary Society Blog.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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Sure, Uranus is big… but how big is it? There are so many ways we can measure the size of Uranus, so let’s look at all of them.

First, let’s take a look at diameter. The diameter of Uranus is 51,118 km across. For comparison, this is about 4 times bigger than Earth.

Now, let’s look at volume. The total volume of Uranus is 6.833×10¹³ km³. Again, for comparison, you could fit 63 Earths inside Uranus, and still have room to spare.

Next, mass. The mass of Uranus is 8.68×10²⁵ kg. This is about 14.5 times more massive than Earth. This sounds like a lot, but this makes Uranus the smallest of the outer planets, smaller even than Neptune.

How about surface area? The surface area of Uranus is 8.1×10⁹ km². This would let you flatten out almost 16 Earths to cover the surface area of Uranus.

How big are the other planets? Here’s how big Jupiter and Saturn are.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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Let’s see how far away Uranus is from the Earth. First consider the fact that both Earth and Uranus are orbiting the Sun. This means that the distance between them can change, depending on their relatively positions in the Solar System.

The closest Uranus can get to Earth is 2.57 billion km.

Imagine Earth, Uranus and the Sun are all in straight line. When Uranus is at its closest point to Earth, the three objects are lined up with the Sun, Earth and Uranus. This is when Uranus is a mere 2.57 billion km. But Earth and Uranus are located on opposite sides of the Sun, they’re at their most distant point. When this happens, they’re 3.15 billion km.

What about the other planets? Here’s how far away Mars, Jupiter and Saturn are from Earth.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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The diameter of Uranus is 51,118 km. Just for comparison, this about 4 times bigger than the diameter of the Earth, at 12,742 km across.

Things get a little more complicated, however. Here’s the thing. As you probably know, Uranus is spinning on its axis, completing a day in just over 17 hours. The rapidly spin of Uranus causes it to flatten out slightly. In other words, the diameter from pole to pole is slightly less than the diameter across the equator. The diameter of Uranus from pole to pole is 49,946. If you subtract the two, you’ll find that the polar diameter is 1,172 km less than the equatorial diameter.

Want more diameters? Here’s the diameter of Earth, the diameter of the Sun, and the diameter of Jupiter, the largest planet in the Solar System.

And do you want more information on Uranus? Nine Planets has a great write up about Uranus, and here’s one from Solar Views.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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The density of Uranus is 1.27 grams/cubic centimeter.

Need a point of comparison? Well, Uranus actually is the second least dense planet in the Solar System after Saturn. The density of Saturn is 0.687 g/cm³. Earth is the densest planet in the Solar System, measuring 5.51 g/cm³.

Want to calculate the density of Uranus all by yourself? No problem. Go grab a calculator and then divide the mass of Uranus (8.68 x 10²⁵ kg) by the volume (6.83 x 10¹³ km³. If you did the math right, you should come out with the same value for the density of Uranus: 1.27 g/cm³.

If you’re looking for more information on the density of planets. Here’s an article about the density of Saturn, and here’s the density of Jupiter.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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A day on Uranus is 17 hours, 14 minutes and 24 seconds. In other words, a day on Uranus is shorter than a day on Earth.

One of the most bizarre things about Uranus; however, is the fact that its axis is tilted to almost 90-degrees. Unlike the other planets, which spin like tops on a table, Uranus looks like it’s rolling around. For part of the year on Uranus, the Sun appears to be move thought the sky, just like we have on Earth. But then, as the year goes on, one hemisphere is in light, and the other is in darkness for an entire season.

What this means is that a day on Uranus is the same as an entire season on Uranus. Even though the planet is rotating on its axis, the Sun will just spiral around in the sky until the planet has gone far enough around the Sun for it to be obscured. Day on Uranus is as long as Summer on Uranus, and night on Uranus is as long as winter on Uranus. Wrap your mind around that…

We have written many articles about Uranus on Universe Today. Here’s an article about the discovery of new moons and rings around Uranus, and an article about Hubble’s view of Uranus.

Windows on the Universe has got a great description of this and a handy graphic to help you imagine it. And you can get more information from the Hayden Planetarium.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.