Category: Astronomy

When it comes to the mighty Jupiter – and seeing Jupiter’s moons through a small telescope or binoculars – timing is everything. Jupiter’s satellites are constantly on the move, and almost any time you observe you’ll see at least one. The four largest of Jupiter’s moons are known as the Galileans, and go by the names of Europa, Callisto, Ganymede and Io. But which one is which and how do you know what you’re looking at?

Thanks to some very cool tools like Sky & Telescope’s Jupiter’s Moon you can tell exactly what time a Jovian event is about to happen and observe it yourself. For example:

Saturday, May 17, 2008

17:36 UT, Io’s shadow begins to cross Jupiter.
18:42 UT, Io begins transit of Jupiter.
19:54 UT, Io’s shadow leaves Jupiter’s disk.
21:00 UT, Io ends transit of Jupiter.

What transpires will look very much like this awesome photo done by Paul Haese. Jupiter Transit events are easy to observe even with a small telescope, but it does require some techniques. First of all, you cannot simply glance in the eyepiece and see it happening with ease. It does require higher magnification and patience! The trick is to get comfortable and just watch… During your extended observing session, moments of stability will come and go and it won’t take long before you notice a phenomena that recurs. The body of Jupiter’s moons are a little more difficult to spot, but the shadow becomes very easy when you take your time and really look!

So what happens if your equipment or skies aren’t up to the task? Never fear… You’re not left out of the game. Timing is everything. Begin by observing Jupiter well in advance of the event and take note of the Galilean moon’s position. By checking every few minutes or so, you will notice when one is about to go into transit because you’ll see it near Jupiter’s limb. Keep watching… Because it will simply disappear! (This is also a great clue for larger telescopes to understand where to look and where the shadow will appear.)

While viewing through the average telescope isn’t going to be as good as what can be seen photographically, just timing and participating in an event is a wonderful opportunity to expand your astronomy knowledge and experience. Watching a Galilean moon transit Jupiter, or Jupiter’s Red Spot is something which can be done from light polluted skies and doesn’t require a lot of technical skills – just patience. Mark your calendars for 3:50 Universal Time on May 22nd when Jupiter will appear to have no moons at all! Try following the event in advance of the predicted time and report what happens. So how many moons does Jupiter have? The real answer is 63. But the question should be…

How many can you see?

This incredible image of an Io transit was done by Paul Haese, a member of MRO, using a Peltier cooled C14 and Skynyx 2-0 monochrome camera with RGB Astronomik filters. Paul’s planetary imaging skills are legendary. The UK has Damien Peach, the US has Don Parker and AU has Paul Haese! Thank you so much for sharing…

[/caption]
Everything we know about Uranus comes from looking through a telescope. Only one spacecraft, Voyager 2, has ever made a close flyby of the planet. Astronomers suspect there is lots of water on Uranus. Since they’ve never actually sampled the surface of the planet, how could they know?

It all comes down to density.The density of Uranus is the second least in the Solar System, after Saturn. In fact, it has a density that’s only a little higher than water. Since water is very common in the outer Solar System, astronomers suspect that the whole planet is made of mostly water. But it’s not like any water you’ve ever seen.

The temperature at the cloud tops of Uranus is 57 K (-357 F), and that temperature increases as you go down at a very predictable rate. It’s believed that the temperature at the center of Uranus is about 5,000 K. Liquid water can’t survive those kinds of temperatures without boiling away, unless you hold it under huge pressure. The water should be a vapor, but the heat and pressure turns it into a superheated liquid.

Did you know that there might be oceans on Neptune? Here’s an article about it.

And here’s some more information about water on Uranus from the Internet. NASA has an article that talks about superheated water on Uranus.

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

[/caption]
Uranus is one of the strangest planets in the Solar System. Something huge smashed into the planet billions of years ago and knocked it over on its side. While the other planets look like spinning tops as they make their journey around the Sun, Uranus is flipped on its side, and appears to be rolling around the Sun. And this has a dramatic effect on the seasons on Uranus.

The Earth’s tilt gives us our seasons. When the northern hemisphere is tilted towards the Sun, that’s summer. And when it’s tilted away from the Sun, that’s winter for the northern hemisphere. But on Uranus, one hemisphere is pointed towards the Sun, and the other is pointed away. The position of the poles slowly reverse until, half a Uranian year later, it’s the opposite situation. In other words, summer for the northern hemisphere lasts 42 years long, followed by 42 years of winter.

If you could stand at the north pole of Uranus (you can’t, you’d sink right in), you would see the Sun appear on the horizon, circle higher and higher for 21 years and then circle back down to the horizon over the course of another 21 years. Once the Sun went below the horizon, you would experience another 42 years of darkness before the Sun appeared again.

You would expect this bizarre configuration to give Uranus wild seasons; the day side faces the Sun and the atmosphere never rotates to the night side to cool down. The night side is in darkness, and the atmosphere never gets a chance to warm up. As the Sun first shines on a region that was cold and dark for years, it heats it up, generating powerful storms in the atmosphere of Uranus. Early observers reported seeing bands of cloud on Uranus through their telescopes, but when NASA’s Voyager 2 spacecraft arrived, it was blue and featureless. It might be that the changing seasons will bring the storms back to Uranus.

Want to learn about the seasons on other planets? Here’s are the seasons on Mars, and the seasons on Saturn.

Here’s an article from the BBC about the changing seasons on Uranus.

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

We’re all familiar with the beautiful rings around Saturn. In fact, you can see them with any backyard telescope. But did you know that Uranus has rings too?

The rings of Uranus were first discovered in 1977 by the astronomical team of James L. Elliot, Edward W. Dunham, and Douglas J. Mink. When he first discovered Uranus more than 200 years ago, William Herschel also reported seeing rings, but that’s probably impossible, because the rings of Uranus are very dark and thin.

Astronomers now know that Uranus has 13 distinct rings. They start at about a distance of 38,000 km from the center of Uranus, and then extend out to about 98,000 km.

Unlike the rings of Saturn, which are very bright and composed of water ice, the rings of Uranus are relatively dark. Instead of containing dust, the rings seem to be made up of larger chunks, measuring 0.2 to 20 m across. These would really qualify as boulders, not dust. They’re also very thin. Each ring is only a few km thick.

Uranus now has a total of 10 known rings.

The rings of Uranus are thought to be very young, not more than 600 million years old. They probably came from a few shepherd moons that were shattered by Uranus’ gravity and turned into rings around the planet. The chunks collided with each other and turned into smaller and smaller particles.

We have written many stories about the rings of Uranus. Here’s one about the rings seen edge on. And here’s another about the discovery of a blue ring around Uranus.

Here’s an article that discusses the discovery of the Rings of Uranus. And here’s a fact sheet from NASA about Uranus’ rings.

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

[/caption]
The more we learn about life on Earth, the more we realize that it can live in some of the most inhospitable places on the planet: encased in ice, in boiling water, and even in places with high radiation. But could life exist elsewhere in the Solar System? Could there be life on Uranus?

Maybe, but probably not.

There are a few problems. The first is the fact that Uranus has no solid surface. It’s mostly composed of ices: methane, water and ammonia. And then it’s enshrouded by an atmosphere of hydrogen and helium. The second is that Uranus is really cold. Its cloud tops measure 49 K (?224 °C), and then it gets warmer inside down to the core, which has a temperature of 5,000 K.

You could imagine some perfect place inside Uranus, where the temperature could support life. The problem is that the pressures inside Uranus are enormous at those temperatures, and would crush life. The other problem is that life on Earth requires sunlight to provide energy. There’s no process inside Uranus, like volcanism on Earth, that would give life inside the planet a form of energy.

Life on Uranus would have to be vastly different from anything we have here on Earth to be able to survive. Of course, it’ll be almost impossible to ever send a spacecraft down into the planet to look for ourselves.

We have written many articles about the search for life in the Solar System. Here’s an article about how life on Mars might have been killed off. And here’s an article about how the soil on Mars might have supported life.

Here’s a link to Hubblesite’s News Releases about Uranus, and here’s NASA’s Solar System Exploration guide.

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

How’s the temperature on Uranus? Cold. In fact, the temperature of Uranus makes it the coldest planet in the Solar System. The average temperature of the cloud tops on Uranus is 49 K (?224 °C).

Why is Uranus so cold? The big problem is that Uranus isn’t generating any heat. The other giant planets in the Solar System actually give off more heat than they receive from the Sun. This is because they’re slowly compacting down, and this generates high temperatures inside their cores. Uranus has a core of only 5,000 K, while Jupiter’s core is 30,000 K. If you removed the Sun, Jupiter would still be visible in infrared telescopes because of this internal warmth, but Uranus would be very dark.

Astronomers aren’t sure why Uranus has such a low core temperature, but they think it has something to do with its bizarre rotation. Unlike the rest of the planets in the Solar System, Uranus is tilted right over onto its side. Scientists think that Uranus has a massive collision early on in its history, which knocked it over. This collision might have also allowed the planet to release much of its internal heat. Others believe that something about Uranus’ internal structure allows it to release this heat more easily than other planets.

We have written many articles about Uranus here on Universe Today. Here’s an article about how Uranus can actually get pretty stormy, and here’s an article about what should be found inside a gas giant.

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.