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Happy Halloween from Hubble!

October 31, 2008 on 7:27 am | In Astronomy, Hubble | 41 Comments

The Hubble Space Telescope, shut down for months now, came back online earlier this week and looks to be working just fine again. Check out its latest picture and see for yourself!

But I’m going to be running around in my Halloween Costume today; pictures tomorrow, I promise. In the meantime enjoy some scary Halloween Astronomy pictures, courtesy of the Hubble Space Telescope.

First up, we have eyeballs, starting with the Cat’s Eye Nebula:

Then there’s NGC 6751, which for some reason isn’t called the Eyeball Nebula:

And now we turn to astro-ghosts, with the Ghost Head Nebula (NGC 2080):

And finally, a little challenge! Can you spot the monster in this picture?

Happy Halloween!

Update: And if you get a chance this weekend, I’ve just been informed that two interesting shows are premiering on the National Geographic channel this weekend: Five Years On Mars this Sunday at 8 PM (about the Mars rovers) and Calling All Aliens after that at 10 PM (about SETI). Check it out if you’ve got time; they sound awesome!

Make(make) me a Planet!

October 29, 2008 on 2:27 pm | In Astronomy, Solar System | 48 Comments

Longtime readers of this site will know that I am a big fan of Pluto, and was disappointed when it was demoted from being a planet to being a dwarf planet.

So I decided to take a close look at all the bodies in our Solar System, and ask the question what are the things about these objects that either make them planets or not planets. We’ve got eight sure things to start from, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Now, let’s think about what these all have in common. First off, they’re all round. Obvious, yes, but this is important. Small objects, like asteroid Gaspra shown below (about 20 km in diameter), don’t have enough gravity to pull themselves into spheres, and therefore it’s not fair to call them planets.

Of all the asteroids in the asteroid belt, only the largest one, Ceres, is massive enough to be called even roundish. The other large ones are noticeably longer in one direction than the others, including Pallas, Vesta, and Hygiea, which are all huge, at over 400 km in diameter! (About the size of Missouri.)

So that’s one point; you’ve gotta be round, or you’re not a planet.

What else? Do you need an atmosphere? Nope; Mercury doesn’t have one, and nobody doubts Mercury’s planethood!

So what else do these eight planets all do? They all orbit the Sun, and nothing else. So this rules out plenty of round things, like all the large Moons in the Solar System (including our own)! Apologies to our Moon, as well as Jupiter’s Io, Callisto, Ganymede and Europa, Saturn’s Titan, and Neptune’s Triton, which are all huge and round. Special apologies to Titan, which even has an atmosphere!

But is that it? Be round and orbit the Sun and you’re a planet? Some people say that should be all, but if so, then what would we do about the Kuiper Belt? You see, out past Neptune, there are a bunch of big, icy rocks in a big belt-like shape; check out a map of our Solar System:

A bunch of them are round, too. Should we make all of them planets? Have a look at what we’ve found so far:

Pluto isn’t even the biggest one; Eris is! So, what do you think? Should Pluto be a planet? Should the biggest asteroid (Ceres) be a planet? Should the other six big, round Kuiper Belt objects be planets? Should we make Makemake a planet? Even Haumea, which is almost as big as Pluto might want to be a planet, even though it isn’t round; should we make an exception because it’s spinning so quickly?

I say no. I say no to all of it. I’d like to have the Nine Classic Planets, including Pluto, and be done with it. But I’m not a voting member of the IAU, and they say that in addition to being round and orbiting the Sun, a planet needs to dominate its orbit. That means no asteroids or dusty debris cluttering its orbit; the planet needs to clear it out. There are lots of good looking candidates that didn’t make the cut; I show you them below:

I don’t like the IAU’s definition of orbit domination, because it seems totally arbitrary. For example, a highly elliptical orbit would not clear out all the junk in its path; does that mean if Jupiter followed Eris’ orbit we wouldn’t call it a planet? Sounds crazy to me. What do all of you think; who should be a planet and who shouldn’t?

Whose Stars Are These?

October 27, 2008 on 1:19 pm | In Astronomy, Q & A | 32 Comments

When you look up at the night sky, one of the first things you learn is that every point of light you see is either a star or a planet:

But what happens if you look through a pair of binoculars? Well, suddenly, you can see a lot more stars than you used to. Because it focuses light coming from a larger region of the sky into your eyes, it lets you see fainter objects. Instead of just about 3,000 stars, binoculars let you see over 100,000 stars! A part of the night sky would look like this instead:

But our technology doesn’t stop at binoculars; we’ve build telescopes, both large and small, that have incredible amounts of light-gathering power! The unaided human eye is about 100 times less powerful than a pair of binoculars, and a small telescope (about 6-8″) is another 100 times more powerful than binoculars are. When you start to use small telescopes, you can see details that are impossible with simple binoculars. Take a look (and click here for the full image):

This is just a picture taken by an amateur astronomer of a comet (the green thing, Tuttle 8P) that happens to be passing by a nearby galaxy (M33, the diffuse thing). And we can see that not everything is a star after all.

But our reader Greg is very savvy, and knows what really powerful telescopes can see.
He asks the following:

Approximately how many of the stars in a picture such as this are in our Milky Way galaxy, and how many are outside our galaxy just floating in space? Is it possible to see individual stars in other galaxies such as Andromeda?

In reality, the largest and most powerful telescopes can see objects that are anywhere between 10,000 and 1,000,000 times fainter than what a small, amateur telescope can see. Let’s take a look at Greg’s picture:

Now there are a bunch of stars in that image, but how do we know which ones belong to our galaxy and which ones belong to Andromeda, which is the closest large galaxy to us? This is a question with an easy answer: they’re all ours! While we can resolve individual stars sometimes in Andromeda, such as Cepheid variable stars, they don’t show up in a normal telescope image like this. How do we know? Let’s take a very similar galaxy to both ourselves and Andromeda, but the only difference is that it’s about 6 times farther away. This is the Sculptor Galaxy:

Notice how it looks very similar to the Andromeda Galaxy, except with far fewer star-like speckles? That’s because all the stars are here, in our own galaxy!

Want to take an extreme case? The Hubble Deep Field and Hubble Ultra-Deep Field images were made by pointing the telescope at a patch of sky known for being completely dark; having no known stars in them. You just sit there and point your telescope there, overexposing the image, and finding what turns up. The results look like this:

But the amazing thing is that every speck of light there is a galaxy; there are no stars in this image. So if we want, we can zoom in on a large, bright galaxy as best we can and see what it looks like:

Notice the absence of individual stars? It’s because they’re all in our galaxy. In fact, if we take that ultra-powerful Hubble Space Telescope and point it, say, at the sculptor galaxy above, we can see some individual stars. But they’re so faint and so miniscule compared to the stars in our galaxy that they get dwarfed. Take a look at the image below: note the foreground star in our galaxy (halfway down, about 1/5 of the way from the left border) and all the other stars, which belong to NGC 253 (sculptor’s scientific name):

See what I mean? They’re all our stars. Looking out at the Universe means looking out through our galaxy, and unbelievably, even in outer space, our own neighborhood gets in the way!

Good question, Greg, and I hope I answered it well for you!

Weekend Diversion: Energy Drinks!

October 25, 2008 on 2:05 am | In Random Stuff | 7 Comments

Finally, an energy drink that gives me the glorious boost I always wanted: Brawndo!

The movie Idiocracy deserves a huge thanks for this one. Now if you’ll excuse me, I have to go win at yelling.

Fire in Space

October 24, 2008 on 12:33 pm | In Physics | 29 Comments

I was thinking about this question the other night and thought I’d find out the answer.

Can you have a fire in space, and if so, how would it be different from fire on Earth?

After all, fire on Earth is a beautiful process.

Combustible materials, usually made of (some combination) of Carbon and Hydrogen, combine with Oxygen at high enough temperatures to form carbon dioxide and water vapor, releasing more energy in the process. The releasing more energy part is key; that’s what allows fires to sustain themselves and grow and spread.

This shouldn’t be a problem in space, mind you. When we go up in space shuttles or the like, we typically take our own oxygen with us, so we can, you know, breathe and live. But there’s something missing from space: gravity.

Zero gravity is, of course, awesome. But why is this important for fire? Let’s take a look at a candle flame, which is a small, controlled example of fire, to understand this. The way this fire continues to live is by consuming fresh oxygen. On the Earth, when air is heated (through fire, for instance) it expands, becomes less dense, and consequently rises. That’s why flames on Earth appear to go up. The hot air, filled with carbon dioxide and devoid of oxygen, rises away from the fire, and cool air sweeps in from below to take its place, feeding the fire.

Now, since there’s no gravity in space, this can’t happen. So what does happen when you light a candle in the zero-gravity environment of space? Let’s take a look:

With no gravity to pull the cool, dense air down and let the hot air rise, the flame is just a sphere! Not only that, but the only way it stays lit is through diffusion; the hot air slowly diffuses outward and the cold air swoops in to replace it. This makes the flame much colder and emit much less light, it makes the candle burn slower, and perhaps most importantly, it makes the fire harder to detect. When they performed this experiment on the space station Mir, the candle flame was undetectable, but the candle burned for 45 minutes instead of the 10 it burned for on Earth.

But how would you discover that you actually had a fire in space? You couldn’t smell the smoke because it doesn’t rise, you couldn’t install a smoke detector, and you wouldn’t be able to see it because the light emitted is so dim. There’s an entire laboratory at UC Berkeley dedicated to understanding combustion in microgravity, and I personally think this is one of the coolest things around! Have a great weekend, and keep on sending in your questions!

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