Category: Astronomy

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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.

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While Jupiter and Saturn are mostly composed of hydrogen and helium, the ice giant Uranus is much different. Instead, it is mostly composed of various ices, like water, ammonia and methane. The mass of Uranus is roughly 14.5 times the mass of the Earth. Astronomers think that between 9.3 and 13.5 Earth masses of this is made up of these ices. Hydrogen and helium only account for about 0.5 to 1.5 Earth masses. The rest of the material in Uranus is probably rocky material.

Uranus probably has three layers inside it: a rocky core at the center, an icy mantle surrounding that, and an outer gas envelope of hydrogen and helium. The core of Uranus is very small, with only half the mass of the Earth. The largest portion of Uranus is the icy mantle. This mantle isn’t exactly ice as we understand it, but it’s actually a hot dense fluid consisting of water, ammonia and other substances. Astronomers sometimes refer to the mantle as a water-ammonia ocean.

We have done many articles about Uranus. Here’s an article about a dark spot in Uranus’ clouds, and here’s a view of Uranus with its rings seen edge on.

Want more information on Uranus? Here’s NASA’s Solar System Exploration page, and here’s NASA’s Uranus fact sheet.

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

In all of those beautiful images of Uranus captured by Hubble and the Voyager, it’s got a blue-green color. How did Uranus get this color?

The color of Uranus comes from its atmosphere. Just like Jupiter and Saturn, Uranus is composed mostly of hydrogen and helium, with trace amounts of other elements and molecules. The third most common molecule in the atmosphere of Uranus is methane (CH₄). This substance causes the blue-green color of Uranus.

Here’s how it works. Although it looks white, the light from the Sun actually contains all the colors in the spectrum, from red and yellow to blue and green. Sunlight hits Uranus and is absorbed by its atmosphere. Some of the light is reflected by the clouds and bounces back into space. The methane in the clouds of Uranus is more likely to absorb colors at the red end of spectrum, and more likely to reflect back light at the blue-green end of the spectrum. And that’s why Uranus has its blue color.

We have written many stories about Uranus on Universe Today. Here’s an article about recent Hubble images of Uranus and Neptune.

This photograph from NASA has one of the best true-color images of Uranus. And here’s more information on Uranus from Hubblesite.

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

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Seen from space, Uranus looks bland, enshrouded in blue clouds. This blue-green color of the planet comes from the fact that the atmosphere of Uranus absorbs the red wavelengths of the visible spectrum, and prevents it from bouncing back out into space. All we can see are the blue-green photons reflected into space.

The atmosphere of Uranus is composted mainly of molecular hydrogen and helium. The third most abundant molecule after hydrogen and helium is methane (CH₄). It’s the methane in Uranus’ atmosphere that absorbs the red spectrum visible light and gives it the blue-green color.

Uranus (and Neptune) have different atmospheres from the larger Jupiter and Saturn. Although their atmospheres are mostly hydrogen and helium, they have a higher proportion of ices, like water, ammonia and methane. This is why astronomers call Uranus and Neptune “ice giants”.

Astronomers believe that the atmosphere of Uranus can be broken up into three layers: the troposphere (-500 km and 50 km); the stratosphere (50 and 4000 km) and the thermosphere/corona extending from 4,000 km to as high as 50,000 km from the surface.

We have written many stories about Uranus on Universe Today. Here’s an article about how Uranus can be stormy, and another about a dark spot on Uranus.

Want more information? Here’s an article from Windows on the Universe about the atmosphere of Uranus. And here’s a Hubble photograph of Uranus’ atmosphere.

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

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Like many planets, Neptune’s orbit isn’t exactly circular. Instead, Neptune orbits the Sun in an elliptical orbit. At its closest point, Neptune gets within 4.45 billion km, and then orbits out to a distance of 4.55 billion km. It takes almost 165 years to complete one orbit around the Sun.

It’s a shame Pluto isn’t a planet any more, because it’s really far. Pluto gets as close as 4.44 billion km. But its orbit is so elliptical that it gets out to a distance of 7.38 billion km. In fact, there are times in Pluto’s orbit when Neptune passes it. Then Neptune really is the farthest planet from the Sun, whether or not you think Pluto is a planet.

What’s farthest object from the Sun? Astronomers think that the long period comets come from a region of the Solar System known as the Oort cloud. It’s possible that this region extends out from the Sun to a distance of 50,000 astronomical units (1 AU is the distance from the Earth to the Sun).

Here’s an article that lists the distances to all the planets.

And here’s an article from Solar Views that talks about the Oort Cloud.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.

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The Sun is hot. Really really hot. But all of the heat and light coming from the Sun comes from the fusion process happening deep inside the core of the Sun. The core of the Sun extends from the very center of the out to about 0.2 solar radii. Inside this zone, pressures are million of times more than the surface of the Earth, and the temperature reaches more than 15 million Kelvin. This is where fusion in the Sun happens.

Every second, 600 million tons of hydrogen are being converted into helium. This reaction releases a tremendous amount of heat and energy.

The process of fusion in the Sun is known as the proton-proton chain. The Sun starts with protons, and though a series of steps, turns them into helium. Since the total energy of helium is less than the energy of the protons that went into it, this fusion releases energy.

Here are the steps.

1. Two pairs of protons fuse, forming two deuterons
2. Each deuteron fuses with an additional proton to form helium-3
3. Two helium-3 nuclei fuse to create beryllium-6, but this is unstable and disintegrates into two protons and a helium-4
4. The reaction also releases two neutrinos, two positrons and gamma rays.

As we said, a helium-4 atom has less energy than the 4 protons came together. All of the heat and light streaming from the Sun came from this fusion reaction.

Here’s an article about how the conditions inside supernovae have been recreated in the lab, and another about a white dwarf star that just shut down its fusion reactions.

Here’s an article from NASA that helps explain how the fusion process works. And here’s a project that lets your students understand the process by making their own fusion reactions.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.

Many of the brightest, most familiar stars in the sky have names. For example, have you ever heard of Sirius – the brightest star in the sky? Or Polaris, also known as the North Star. If all these stars have names, does the Sun have a name?

Actually, the Sun doesn’t have its own name, apart from “the Sun”. But “sun” is also a generic name that you can use for any star. Sometimes people say that a star has the mass of 20 suns, or planets orbit other suns. You might have heard the term “sol”, but that’s just another name for Sun, based on the Roman God of the Sun.

We now know that the Sun is just a star. And so, it can be classified into categories like the other stars in the Universe. Just in case you were wondering, the Sun is a G2V star. The G2 part refers to the spectral class, and the V part is the luminosity. Stars with the “V” designation are in the main-sequence, or hydrogen burning, phase of their lives.

So it’s kind of strange to say, but Sun has no scientific name or designation, apart from, “the Sun”. Every other star in the sky does have a scientific designation.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.