And even after making those decisions, this list is still twice as long as the usual ones! Still, I think you'll agree that every single one of these two dozen images is simply breathtaking, either through sheer beauty or because of the fantastic story they tell. This year, the images are dominated by Hubble for some reason - I mean sure, Hubble pix are amazing, but there's just a lot this time around. Also making multiple appearances is WISE, an infrared survey observatory that shut its eye in March of 2011. Again, those images are just, well, wow. You'll see.

So go ahead and click away. To browse, just click the arrows or the next image in the filmstrip. Clicking the image will take you to my original blog post about it, with more information.

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RCW 120 is one such nebula, located over 4000 light years away in the constellation of Scorpius. Several stars are in the process of being born here; look right in the center and you'll see a blue speck; that's a star that's already far larger and more powerful than the Sun. It floods the nebula with ultraviolet light and blows out a mighty solar wind that's compressing the gas around it, forming the bubble shape of the overall cloud. Other stars are forming around the rim of the bubble, and one of them is already massive enough that its fate is sealed: one day, million of years from now, it will explode. So will the star in the center, in fact, though it's unknown which will blow its top first.

Either way, get a good look now: in a million years or so RCW 120 will be torn apart by the expanding debris from a detonated star.

Image credit: NASA/JPL-Caltech

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It's a spiral galaxy, like ours. It has multiple arms, wound fairly tightly, like ours, several of which split and have disconnected spurs, like ours. It even has that rectangular feature in the middle called a bar, caused by the odd gravitational interactions of several billion stars as they orbit near the galactic center. If you could travel a few hundred thousand light years straight out of our galaxy, you'd see something very much like UGC 12158.

...except for one small thing. Actually, a big thing: the Milky Way is among the biggest galaxies in the Universe, being 100,000 light years from side-to-side. But UGC 12158 has us cleanly whipped in the size department: it's 140,000 light years across! That's huge! Only a handful of spiral galaxies are bigger than this, making it one of the bruisers of the cosmos.

Image credit: ESA/Hubble & NASA

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This cycle is played out everywhere, including the weird trunk-like nebula called IC 5146, seen here in the far-infrared by Europe's space-based Herschel Observatory. The light you're seeing here has wavelengths hundreds of times what our eye can see, meaning it has hundredths the energy. This stuff is cold; mere degrees above absolute zero. What's glowing here is actually quite dark in visible light, with the exception of the glob on the left, which is where stars are being born - they light up the surrounding gas, making it visible to us.

But that long filament that stretches to the right? That is actually dust that's been riled up by exploding stars. When a supernova goes off, a shock wave of material blows away from it. That wave slams into waves from other stars that have exploded, and the gas gets all mixed up, like contrails from two passing jets. It's turbulent, and that tends to create long filaments like the one in IC 5146. They're all over the sky, a testament to the number and sheer power of supernovae. And that gas can compress, too, and form new stars... starting that cycle all over again.

Image credit: ESA/Herschel/SPIRE/PACS/D. Arzoumanian (CEA Saclay) for the “Gould Belt survey” Key Programme Consortium

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M15 was always one of my favorites as a young man, standing with my 'scope at the end of my driveway in the late summer and early fall when Pegasus and the cluster were high in the sky. Bright, large, and easy to find, it was so pretty that I would stare at it and wonder what it would be like to be on a planet inside there, with hundreds of stars blazing away as bright as Venus...

What I didn't know then is that one particular star was different. Just below and to the left of the cluster center is a vividly blue star (see the super-duper high-res embiggened version to get a better look). It turns out that's a star like the Sun, but it's dying. It's shedding material at a furious rate, and lighting it up like a neon sign. Although it has nothing to do with planets, this is called a planetary nebula. While globular clusters are billions of years old, the planetary nebula phase of a star's life only lasts for a few thousand years, so it's exceedingly rare to find them in globulars. And even though it's marking the end of a star's existence, that flash of cerulean blue makes this cluster just that much more exquisite.

Image credit: ESA/Hubble & NASA

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Because it's such a big star, it's blowing a big wind, like a super solar wind. This gas is slamming into and compressing the material floating in between stars, lighting it up. This image shows the result: taken by NASA's Wide-field Infrared Survey Explore, what you see as green is undisturbed dust, but the yellow shows where this material is getting rammed by the star and its wind. It's very similar to the bow wave you see off the front of a ship as it moves through water... but on a somewhat larger scale.

And while this structure was born in violence - a supernova is as nasty as it gets in the Universe, pretty much - and glows from violence, it's amazingly delicate-looking and wondrous. From a safe distance, the Universe can be really lovely... from a very safe distance.

Image credit: NASA/JPL-Caltech/UCLA

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Because they're big, sometimes galaxies get close together. Too close. Close enough that their gravity can affect each other, drawing out long arms of gas and stars, distorting each other into weird and beautiful shapes. It happens a lot.

Such is Arp 273, seen here in a Hubble image taken to celebrate the observatory's 20th anniversary in space. These two big galaxies passed each other in the recent past (like, a few million years ago). Both were probably normal enough before the encounter, but are now twisted and asymmetric. Reds and yellows are dust and old stars, and blue is where the recent collision has spurred star formation. And you might think this is a remote event that doesn't affect us at all - and at 300 million light years distant, you're right - but keep in mind that a similar fate awaits us and Andromeda... in a billion years or two.

Image credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)

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But on further examination, this event turned out to be more amazing than usual. The way the explosion got brighter and then faded didn't match with what we knew of the usual flavor of gamma-ray bursts. In fact, the only thing that made sense was that astronomers had witnessed what nightmares are made of: an entire star being literally torn apart by the ferocious gravity of a black hole!

The scale of this disaster is staggering: octillions of tons of matter were ripped away from the star, shredding it entirely. This material fell around and formed a disk circling the black hole, heating up to millions of degrees, and blasting out a beam of energy that marched across the Universe for four billion years until it fell into Swift's detectors. The image above shows the hard X-rays (seen here as red and yellow) as well as visible and ultraviolet light (white and purple) detected by Swift. The linear rays coming out of it are an artifact of the telescope and aren't real, but they do lend some drama to the image.

And what can be more dramatic than this? Most stars end their lives either slowly fading away or exploding as a supernova. To be torn apart by a black hole... well. What a way to go!

Image credit: NASA/Swift/Stefan Immler

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That last bit doesn't take long, only a few thousand years before the gas expands so much it becomes too thin to get lit up and be seen. What's even shorter is the time between the star shedding those outer layers into space, and when they get lit up in the first place. That phase is called the proto-planetary nebula, and is so short that only a few of these objects are known. One of them is IRAS 13208-6020, seen here in a Hubble image. The gas there isn't glowing on its own just yet; it's simply reflecting the light from its star. Very soon, perhaps in the next millennium or two, the star you can see in the center will shed those last bits of gas on top of it, exposing it fully to space, and the weird lobes of material will glow far more brightly, becoming a planetary nebula proper.

Nebulae like this come in all sorts of shapes, from almost perfectly round to extremely elongated like this one. We suspect that this may be due to planets orbiting the star getting swallowed up as the star expands; the orbiting planets whip it up like an eggbeater and focus the gas into these fantastic shapes. So oddly, planets do have something to do with planetary nebulae. It's funny; sometimes art imitates nature, which then turns righ around and imitates art.

Image credit: ESA/Hubble & NASA

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This false-color Hubble picture is taken in the near-infrared, just outside the range of what our eyes can see. This is where warm dust is very bright, and the swirling pattern you see is from all that dust. Normally, a picture like this would show lots of stars as well as dust lit up by those stars, but astronomers used an image taken in visible light to subtract off the stars in the IR image, leaving just the dust behind.

This picture shows just the inner region of the galaxy, an area about 18,000 light years across. The dust is following the spiral arms of the galaxy, and is clumpy... but not as clumpy as was expected. M51 is interacting with a nearby galaxy (off screen here) and that gravitational barn dance may be what's smoothing out the dust here. Or it might be something entirely different. We're not exactly sure. Images like this one will help astronomers understand how dust behaves inside galaxies, which in turn will help us understand galaxies as a whole.

And, since we live inside a galaxy ourselves, this strikes me as a good idea. It's always nice to explore your own neighborhood.

Image credit: NICMOS Image: NASA, ESA, M. Regan and B. Whitmore (STScI), and R. Chandar (University of Toledo)

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M43 is a nebula, a cloud of gas actively churning out stars. Located in Orion, it's easily seen even in binoculars, but when you use Hubble, you get some fantastic detail. In this image we're seeing stars in the act of forming, and the violence of their birth is displayed. Stars form from whirling disks of material; the centers collapse to form stars, and the outer parts can coagulate to become planets like Earth. When the star is still very young, it blows off huge amounts of material. Magnetic fields as well as the presence of the disk tend to focus this material into beams, like two flashlights taped end-to-end. The outward-rushing matter slams into the junk floating in space around it - at speeds upwards of a million kilometers per hour! - puffing it up into elongated teardrop-shaped lobes. You can see one of these objects just left of center in this image. There's probably another lobe, hidden behind thick layers of opaque dust.

To the right and just below the bright star near the top of this image you can see a little flare of white light. This is actually the glow from an infant star, and in the high-res image you can see this looks like a hamburger; the patty is actually the disk of material seen edge-on. A few years back we knew such objects must exist, but it wasn't until Hubble that we got such clear views of them. We can now actually observe stars in every single stage of their lives. It's an amazing time to be an astronomer... or to be someone who appreciates the beauty of astronomy.

Image credit: ESA/Hubble & NASA

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Fast forward ten years. In 2008, planets were indeed found orbiting HR 8799. Those observations, using the ginormous Gemini 8-meter telescope, were among the first exoplanets directly imaged (as opposed to inferred using indirect techniques), and they made up the first exoplanet solar system ever directly seen.

Armed with this knowledge, in 2011 astronomers went back and looked once again at the 1998 Hubble data. Using sophisticated techniques and data unavailable 13 years ago, they were able to painstakingly subtract the light from the star, removing its glare, and revealing the planets as seen in the image above. In a sense, this image was the very first one to ever directly show exoplanets, but in reality that's not entirely fair.

Still, it's an incredibly important image: it gave us an extra 13 year baseline in observing these planets, long enough to actually detect their orbital motion around their star! The three planets seen take 100, 200, and 400 years to orbit once, so even these few years of extra data have helped astronomers understand better planets orbiting another star, over a thousand trillion kilometers away.

Image credit: NASA, ESA, and R. Soummer (STScI)

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It's because it lies in the plane of the Milky Way galaxy, and is dimmed to obscurity by all the dust in our galaxy - it's like trying to look out of room filled with smoke. But infrared light can travel through all that junk pretty well, so the view from NASA's Wide-field Infrared Survey Explorer (WISE) is unparalleled.

The galaxy is actually pretty amazing. You can just make out the spiral arms, narrow and long, making a giant S in the sky; those were not seen before WISE took a look. But the picture is dominated by the galaxy's core, which in infrared outshines the rest of the galaxy's light combined. At the nucleus of Circinus is a monster black hole, and matter is spiraling into it. As it does so, it heats up to fantastic temperatures, blasting out X-rays and other forms of energy. This radiation heats up the dust around it - most galaxies are littered with the stuff - which then reradiates that away in the infrared. If you look just outside the intense core, you'll see a ring of light: that's probably where a lot of stars are forming, which again creates more dust that can glow in the IR.

Observatories like WISE open up a new window on the Universe, giving us a view of the sky that we might have otherwise missed... even when something is almost literally right next door.

Image credit: WISE: NASA/JPL-Caltech/WISE Team

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Abell 2744 is a cluster of galaxies; thousands of galaxies swarm inside of it. But new observations reveal a startling result: it's actually the collision of four separate clusters of galaxies, all slamming into each other at the same time! The amount of material involved is staggering, beyond belief: over four hundred trillion times the mass of our Sun! That's well over a thousand times the mass of our entire Milky Way Galaxy.

Yikes.

This picture shows the object, nicknamed the Pandora Cluster. It combines visible light images from Hubble and the Very Large telescope (shown in blue, green, and red) - which show gas and stars - with X-ray images from Chandra (shown in pink) which picks out extremely hot gas in between the galaxies, heated by the collision. The region colored vivid blue is actually a model showing where dark matter lies: this invisible stuff makes up most of the budget of the Universe's mass, but is not directly viewable. However, it has gravity, and that distorts the light coming from more distant galaxies behind it. By carefully mapping out that distortion, the location and amount of dark matter in the cluster can be determined. Clusters like Pandora house a lot of dark matter, and are great places to look for it.

Dark matter doesn't interact with normal matter, but regular old gas sure does. When clusters collide, so does their gas, which can screech to a halt in a head-on collision, while the dark matter blows right on through. By mapping where normal matter is compared to where the dark matter is, the history of the cluster can be found, and that's how astronomers figured out four separate clusters were involved.

The next time you get involved in a fender bender in a car, keep that in mind! Things could've been a lot, lot worse.

Image credit: NASA, ESA, ESO, CXC, and D. Coe (STScI)/J. Merten (Heidelberg/Bologna)

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Brown dwarfs don't generate any heat through fusion, so once formed, they just basically sit there, cooling off. Once they're a few billion years old they're pretty hard to spot, since they don't give off much light. They're brightest in the infrared, and that's how most are discovered. The hotter they are the easier they are to find, and most have temperatures around 1000°C, much hotter than your oven (but far cooler than, say, the Sun).

WISE, NASA's Wide-field Infrared Survey Explorer, was a brown dwarf-finding machine, since it was built to look at just the wavelengths brown dwarfs emit. It's found quite a few, and most were easy to spot - due to the way the images were put together, brown dwarfs appear green in the pictures (though really the colors of brown dwarfs in visible light vary wildly). You can see one circled in the image above - it's called WISE 1828+2650 and what's amazing about it is that its temperature is a mere 25° C! That's right: it's basically room temperature. Now, it's actually a giant ball of gas the size of Jupiter but with probably dozens of times the mass, so you'd be crushed to death if you could stand on its surface, which you couldn't, because it doesn't really have a surface. But you'd be at a comfy temperature while it happened.

I studied brown dwarfs for a while when I was working on Hubble; at the time we didn't know much about them but I found them fascinating. And now I can say, without fear of being contradicted, that they are literally cool.

Image credit: NASA/JPL-Caltech/UCLA

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It's about 30 - 40 million light years away, neither really close nor really far. It's maybe 70,000 light years across - smaller than our Milky Way, perhaps average for a spiral. It's not blasting energy out of its core as some galaxies do, nor is it totally quiet, like the Milky Way is. It doesn't have gigantic regions of star formation in its arms, it doesn't have a rectangular bar in its center, it doesn't appear to have large satellite galaxies. It's a run-of-the-mill, everyday, neither-here-nor-there galaxy.

But that's what makes it special: it's a control, a gauge, a ruler against which to measure other galaxies. How do you know if some galaxy is acting bizarrely if we don't know what normal is? NGC 2841 is normal.

But it's still gorgeous. I love the way the central region looks smooth and uniform, but the dust clouds in the arms are patchy, crinkly like the top of a snickerdoodle. Sometimes in these lists I like to pick the extreme objects, because in many cases in the extreme there lies beauty. But there can also be beauty in the mundane as well.

Image credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration Acknowledgment: M. Crockett and S. Kaviraj (Oxford University, UK), R. O’Connell (University of Virginia), B. Whitmore (STScI) and the WFC3 Scientific Oversight Committee

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Among the most famous of them is NGC 6543, the Cat's Eye Nebula, named for the shape of the central region; it does resemble the eye of a cat. But in this very deep exposure taken using 2.5 meter Isaac Newton Telescope on the island of La Palma in the Canaries, we're seeing much more than that. It reveals the far fainter outer material, shed millennia ago by the star. This outer halo is pretty big: 6 light years across! Most planetary nebulae are only a light year or so across, so this is a fantastically vast and gossamer structure.

The knots and clumps are where the expanding gas encountered material between the stars, compressing it and forming those tendrils. Giant halos around planetaries are hard to observe because they're so faint, but several have been seen. They're like the preserved remnants of an ancient star, and examining them is like doing astronomical archaeology... on a scale 60 trillion kilometers (40 trillion miles) across.

Image credit: This image was obtained and processed by members of the IAC astrophotography group (A. Oscoz, D. López, P. Rodríguez-Gil and L. Chinarro).

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So what is it? It may very well be an image - the very first image ever - of a planet caught in the act of formation. How cool is that?

It's name is LkCa 15b, and the image was taken by the massive 10-meter Keck telescope in Hawaii. This is an infrared image, where the blue and red colors indicate different colors of IR light. Astronomers were observing a very young star (the position of which is marked in the image by the star shape) known to have a disk of material surrounding it, the kind that forms planets. The disk is actually an annulus, like a DVD with a hole in the middle. The hole is not completely devoid of matter, though. This picture is a closeup of a part of the material in the hole, and it may very well be that the blue spot is a planet, and the red swirl is material falling onto the planet - in other words, the planet is still forming from junk orbiting the star!

The researchers make a pretty good case of eliminating other possibilities (a background star or galaxy, for example) and all in all it really does look like they caught this planet while it was still accreting material. Like I said, it's not 100% certain, but the data look pretty convincing to me. It may turn out to be something else - there's always that possibility when doing cutting edge science - but either way, it's a very odd object and worth further study. And if it does turn out to be an infant planet, then it's an amazing discovery, and will be a boon to the science of planetary formation.

Image credit: Kraus and Ireland

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