Category: Guide to Space

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…

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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.

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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.

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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.

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Uranus has a mass of roughly 14.5 times that of Earth, which makes it the least massive of the giant planets. Astronomers know that it’s mostly made of various ices, like water, ammonia and methane. And they theorize that Uranus probably has a solid core.

The core of Uranus probably only accounts for 20% of the radius of Uranus, and only about 0.55 Earth masses. With gravity of all the outer mantle and atmosphere, regions in the core experience a pressure of about 8 million bars, and have a temperature of 5,000 Kelvin. That sounds hot, like as hot as the surface of the Sun, but keep in mind that the core of Jupiter is more like 24,000 K – much hotter. The core of Uranus has a density of about 9 g/cm³, which makes it about twice as dense as the average density of the Earth.

For astronomers, Uranus has an unusually low temperature; and that’s a mystery. One ideas is that the same impact that knocked Uranus off its rotational axis might have also caused it to expel much of its primordial heat. With the heat gone, Uranus was able to cool down significantly further than the other planets. Another idea is that there’s some kind of barrier in Uranus’ upper atmosphere that prevents heat from the core to reach the surface.

We have written many stories about Uranus on Universe Today. Here’s an article about a dark spot in the clouds on Uranus, and here’s an article about the composition of 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.

Choose Your Observing Site To Use A Telescope

One of the most important things to begin with is to carefully choose the site you will use set up and use your telescope at. While it would be tempting to take your new telescope out of the box and use it that night, it’s best to wait just a day or two! Begin the first clear night by going outside a taking a good look around. You want to choose an observing site where the view is as unobstructed and as dark as possible. While you are doing this, keep in mind that it must be comfortable to you as well. While the vista might be far improved a kilometer away – do you really want to have to take your equipment that distance each time you want to use it? Look at many different alternatives. If you live in a city, perhaps a rooftop will serve well. Urban settings often have very suitable yards that will work for most observing projects and rural settings are ideal.

Light pollution is another factor when choosing your site. Again, keep in mind that you must have a site that is accessible to enjoy. It isn’t always possible if you live in a well-lit area to take your equipment remote each time you want to use your telescope – but a sheltered area, such as in the shadow of a house, often blocks stray light well enough to enjoy using your telescope right at home. Of course, finding a dark sky site is also important, too. But not half as much as just finding a spot that you will enjoy and use.

While out during the day, look for level, solid ground. No one wants to see their telescope take a tumble. While it is tempting to set up on a deck, remember that any footsteps will cause vibration in the image. Setting up on places like a blacktop driveway or concrete can also cause thermal issues, too. Avoid them when you can, but do not discard these types of sites if they are comfortable and accessible.

How To Set Up Your Telescope

While every telescope set-up is slightly different, they are all basically the same in some respects. There must be an optical tube of some type, a mount and eyepieces. Take the time to become familiar with all the components of your telescope! If you must assemble and dis-assemble your telescope each time you use it, it’s a very wise idea to practice a few times before you go out in the dark. There is simply nothing more frustrating that trying to learn to set up your equipment when you cannot see what you are doing – or to loose a small part in the dark. If it is at all possible, leave your telescope and tripod fully assembled and in a place where it is easy to set outside at a moment’s notice. You’ll find that you’ll use it far more often if it takes less work.

Your telescope’s view is also dependent on ambient temperature. If you wear eyeglasses, you understand why! If you go from a very cool environment, such as a air-conditioned house, into a humid outdoors setting, your glasses fog up, don’t they? And so will your telescope’s optics. The same is true when observing outdoors in the winter. When taking your telescope from a heated climate to a cold one, you must give the telescope time to “cool down”. Even just a few degrees can mean waiver in the image.

Align your finderscope in advance! While this sounds rather strange, another frustrating thing to do in the dark is to align a finderscope – especially on a moving target. Once you have learned to assembly your telescope, learn to align your finder. Set up your scope and aim at a distant object. Now align your finder to that object as well. This will make things much easier, later!

Once your telescope is set up, the last thing to remember is to stow your things neatly so you won’t have any problems finding them when it comes time to put things away. Dust covers and eyepieces cases are so easy to lose. Keep things neat and you won’t have any problems. Choose the eyepiece you think you will need in advance and have them in a place where you won’t need to fumble in the dark. Have your red flashlight and maps handy. These are just little things that make using your telescope much more enjoyable!

Choose Your Observing Times

Experience will become your best teacher. It won’t take long before you realize that very humid nights or exceptionally cold ones are not particularly good times to observe. Unless you plan on looking at the Moon itself, nights that are well moon-lit are also not good times to search for a faint galaxy, either. Little things, like waiting for a planet to clear the atmospheric “murk” at the lower horizon mean a much better viewing experience.

How To Use A Telescope

Now that you have your observing site, learned to set up, and established a time to practice astronomy… Let’s learn how to use your telescope!

If you have an equatorial mount, align the axis to the pole star. Altazimuth mounts do not need this step. Take off your dustcaps and stow them away. Double check to make sure your tripod legs are secure. Choose your low power eyepiece and put it in the focuser. Are you ready? Now, loosen the axis and take aim at a star using your finderscope. When the star is aligned in the center of the finder, tighten the axis and it’s time to go to the eyepiece. Gently adjust the focus in or out until you have a crisp, clean image. Now watch the star move. This direction is always west – regardless of the orientation in the eyepiece. For equatorial mounts, use your slow motion cables to learn to “track” the star. For altazimuth mounts, use the pan control or shift the tube manually (dobsonian models). Once you have learned to “follow” and object, it’s time to star hop!

Each time you go to a new object with an equatorial mount, you must unlock the axis. The same is true with some styles of altazimuth mounts. Once you have the general location in the finder, lock the axis back up and use the slow motion cable controls or panhandle control to make small moves. Using a low power eyepiece first will help you locate things much easier, and you can then switch to more magnification once the object is located.

When you are finished for the evening, make sure to replace all your dustcaps. If your optics should become dewed, don’t wipe them off. Allow them to air dry to avoid micro-scratches on delicate coatings. Always make sure to give your observing area one last check before leaving just in case you’ve forgotten something!

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Uranus is a ball of ice and gas, so you can’t really say that it has a surface. If you tried to land a spacecraft on Uranus, it would just sink down through the upper atmosphere of hydrogen and helium, and into the liquid icy center.

When we look at Uranus, we see the blue-green color that seems to come from the surface of Uranus. This color is light from the Sun reflected off Uranus’ surface. The atmosphere of Uranus contains hydrogen and helium, and most importantly, it has relatively large amounts of methane. This methane absorbs color in the red end of the spectrum of light, while photons at the blue end of the spectrum are able to reflect off the clouds and go back into space. So the full spectrum of the Sun’s light goes in, the red and orange end of the spectrum is absorbed, and the blue green end of the spectrum bounces back out. And this is why the surface of Uranus has its color.

But let’s imagine that the surface of Uranus was actually solid, and you could walk around. You might be surprised to know that you would only experience 89% the gravity that you feel back on Earth. Even though Uranus has 14.5 times more mass than Earth, it has 63 times the volume of Earth. Uranus is the second least dense planet in the Solar System, so it has a relatively weak gravity on its surface.

We have written several articles about Uranus for Universe Today. Here’s a story about what’s inside a gas giant, and here’s one about two new moons discovered for 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.