This past year has been -- like most are -- up and down for science in general and astronomy in particular. We've had stunning successes and heartbreaking setbacks, all of which seem huge when dealing with them at the time. But while the science of astronomy is many things, one of the more subtle yet deeply profound aspects of it is its ability to provide a sense of perspective.
The year's end is a traditional time to look back and try to gain perspective on the events that occurred during this last circuit of the Sun. Astronomers have been hammering away at the sky, taking images that have profoundly pushed forward our understanding of the Universe. But there's been more than that, too. They've slapped down some bad science -- and deleting a negative is indeed a positive. They have also looked at old things in a new way, or new things in a new way, and even some new things in an old way.
With all this in mind, I decided to create my list of Best Astronomy Pictures of 2006. I went through hundreds of images (maybe thousands), checking NASA, APOD, the ESA, BAUT, and a few dozen amateur and professional sites featuring pictures as well. The criteria I kept in mind were beauty, of course, but also scientific value. But both of these could be trumped by the coolness factor. All three are subjective, but what the heck. It's my blog. So here is what I came up with.
All the images below are hosted at Flickr, and they link to the original sites with higher resolution images (many of the pictures are suitable as wallpapers).
Remember, it's my list. If you disagree, or you agree but don't like my ordering, then post a comment! Let's see what you think should have been here. Maybe I'll post my runners-up list.
Number 10: The Comet and the Ring
A comet almost had to make this list, since they're so darn pretty. But there was one this past year that, to me, was extra cool.
Periodic comet 73P/Schwassmann-Wachmann (say that three times fast) was discovered in 1930, and in 1995 it was seen to have broken up into many pieces, most likely due to heating from the Sun. The fragments passed close by the Earth once again in May 2006, where many were easily visible through binoculars (I saw them myself, both through my binocs and my 'scope).
The comet was big, bright, and passed by many astronomical showpieces... including the famous Ring Nebula, a cloud of gas a light year across ejected by a dying star. When the two were close together, astronomers Paul Martinez & Philip Brents took this spectacular shot:
The Ring is the disk-shaped object in the upper left. Here's a close-up of it:
A lot of images were taken of this pairing, many showing more detail and with the comet closer to the Ring, but this image speaks to me (in fact, it's my desktop image at work). The scale is big-- a lot of sky is in this shot, and it shows better the contrast in apparent size between the two objects. The comet looks bigger only because it's so much closer: the Ring is actually about 10 trillion times bigger than the comet! But it's a tad bit farther away.
Number 9: Painting the Eclipse
Lunar eclipses are fairly common: the Moon passes into the Earth's shadow roughly once or twice per year on average. Since the Moon is bright and easy to photograph, there are zillions of lunar eclipse pictures available to view.
I thought I'd seen 'em all, but then I saw this one and it floored me:
How cool and wonderful is that? The photographer, Laurent Laveder, set this image up very carefully, making sure that the model was placed just so when the Moon was just starting to be eaten by the circular edge of the Earth's shadow. The result was this very clever tongue-in-cheek photo. I love it! He has many more images on his site worth checking out, too.
I also wrote about this image in September 2006, and have some more comments there.
Number 8: The Tarantula Writ Large
Our Milky Way Galaxy is a giant spiral collection of stars, gas, and dust. It has many smaller satellite galaxies, and one of them is the Large Magellanic Cloud, or LMC. The LMC is a fuzzy cloud-like object easily visible to the naked eye if you happen to be far enough south of the Equator (I saw it with my own eyes from Canberra, Australia in 2004). Through a telescope, though, the LMC is dominated by a cloud of gas called the Tarantula Nebula, perhaps the most active stellar nursery known.
You've probably seen images of the Orion Nebula, right? At 1500 light years away, it's one of the brightest nebulae in the Milky Way, and is easily visible to the unaided eye. It's about 30 light years across.
The Tarantula, however, is 160,000 light years away, and yet is still about as bright to the eye as the Orion Nebula. That's because it's frakking huge: it's something like 1700 light years across, fifty times Orion's size! If the Tarantula were placed at the distance of the Orion nebula, it would fill half the sky.
And so is this next image. The good folks at the European Southern Observatory stitched together several images of the Tarantula to make a mosaic of it that has 256 million pixels. Let's see your store-bought camera do that!
This is a very, very compressed image of the big one. You could download an insanely monstrous 211 Mb 9000 x 8000 pixel image, but I recommend you go to their zoomable image of it instead, and tour around it. See if you can spot Supernova 1987A, a star which blew up and eventually led to me getting my PhD.
But try not to get lost. It's a big place.
Number 7: The Face Defaced
Ah, the "Face" on Mars. Where would Richard Hoagland be without it? Shilling some other snake oil, I would guess.
But that's a dream; people promoting antiscientific garbage always find some way to offload their claptrap. Still, it's always nice to see them slapped in the face -- or the Face -- by reality.
This next dose of reality comes courtesy of the European Space Agency, whose Mars Express orbiter took some great high-resolution images of the Cydonia plain on Mars where the face is located. By taking images from different angles and with varying solar illumination, they were able to create a three-dimensional image of the "Face". Perhaps when this image was released Hoagland waited with bated breath to see his ravings confirmed, but that'll be a long, long wait:
Wow, it's uncanny, isn't it? It looks just like a face... if that face was hit repeatedly with high speed projectiles and then covered with lumpy mashed potatoes.
That's no face... it's a butte! Yes, I know it's actually a mesa and not a butte, but let a guy have a joke at someone else's expense once in a while, OK?
Anyway, the ESA also put together a nifty 3D rotating animation of this, and there is another image taken from a different angle as well. That last one is marginally more face-like, but you have to kinda squint really hard to see it. There is also a cool suite of "Face" images online as well.
Number 6: Robots on Mars
Speaking of Mars, we humans have been sending our machines there for a long time. We still lose the odd one or two (getting to Mars is pretty hard in reality), but in general we've been getting better at it, and better at building them as well.
In 2006, the Mars Reconnaissance Orbiter switched on its HiRISE camera, a phenomenal device capable of taking images of the Red Planet's surface with half a meter resolution. The pictures returned have been devastatingly amazing, with an incredible scientific return, but sometimes the best pictures have little scientific value, but are still, well, cool!
This is a very small piece of a HiRISE image of Victoria crater on Mars, showing just one part of the rim. And sitting right there on the edge of the crater is a little metal robot named Opportunity. Launched in July 2003, that rover was designed to work for only 90 days, yet it just celebrated its 1000th day on Mars! You might have a hard time seeing it in that image, so here's a close-up:
There it is! You can see the shadow of the camera mast, and even the tracks of the rover.
Of course, I know in my brain that Opportunity is sitting on Mars, and I have seen all sorts of pictures it's taken of itself. But somehow, seeing that image makes it really real.
We have robots on Mars! Humans are so smart.
Number 5: The Shuttle, the ISS, and the Sun
I still think it's funny that most people are unaware that they can see man-made satellites easily with the naked eye. There are even websites that can tell you when a given satellite will pass near you!
The Shuttle, when it's up, is a pretty bright object, as is the International Space Station. So if you do your homework and plan your observation extremely carefully, you just might make my Top Ten list.
Thierry Legault did just that. Not only did he get a picture of the Shuttle and the ISS, he nailed them while, from his viewing point, they were passing directly in front of the Sun.
This shot is simply stunning, and shows a tremendous effort in planning, timing, and execution. The picture was taken on September 17, 2006, less than an hour after Atlantis had undocked from the ISS. By capturing them in silhouette against the Sun, he could take such a short exposure that any atmospheric distortion was frozen out. This means he got incredible detail in his picture. Take a look at the zoomed image:
You can see different structures on the ISS, and even the vertical tail on the Shuttle! Given that the spacecraft were hundreds of kilometers away from Legault, this picture is truly an amazing feat.
This next picture takes a moment to set up, so please forgive me. Plus, I like to lecture sometimes.
As I was perusing images, I realized I didn't have many that had strong scientific value, which was ironic. But that happens: most scientific images aren't published because they're pretty, and pretty pictures sometimes only get in the news because they're pretty. But there was one image this year that has both beauty and a far deeper scientific significance.
It's been known for decades that there is a lot of dark stuff out in space, between galaxies. We see its effects on the way galaxies rotate, and the way they behave when they live in clusters (like a city of galaxies). We know that this dark matter is ten times as common as regular matter (like the stuff we are made of: atoms of hydrogen, carbon, oxygen and so forth), but it was undetectable, so it was somehow different than normal matter. But how, exactly? No one was sure.
One theory was that dark matter was made of weird particles that could interact with normal matter or other dark matter through gravity, but that was it. In other words, two colliding clouds of dark matter could pass right though each other like ghosts.
But how do you detect something like that? One way is through gravitational lensing. Matter has gravity, and gravity bends light. So if matter, even dark matter, gets between you and some distant object, it can act like a lens, distorting the light from the more distant object. By mapping out those distortions you can "see" dark matter.
So you know what those clever astronomers did? They looked at two colliding clusters of galaxies, which together are called the Bullet Cluster. Galaxy clusters have lots of gas pervading them, like fog in a city. When the clusters collided, the gas from each cluster smacked into the other head-on, grinding them to a halt. But if the dark matter is really this ethereal stuff it would keep on going, undeterred. If this were the case, you'd see the normal matter from the cluster closer to the center, with the dark matter on the outside.
And behind door number two...
Voila! The pinkish light is coming from the normal gas in the cluster. The dark matter reveals itself through its gravitational distortion of more distant objects, which is colored blue here. And look! The dark matter is on the outside, and the normal matter on the inside, just as predicted!
To an astronomer, this is completely convincing evidence that dark matter is real, and that the majority of the Universe is made up of stuff we simply don't understand. What is it? Beats me, and it beats a lot of other scientists, too.
I love mysteries! That means there's more to learn.
Number 3: Solar Shock Wave
The next image on my list makes me a little sore. When it was released I was busy and figured it wouldn't be that interesting. I was completely wrong.
The Sun has a powerful magnetic field. The surface of the Sun is so hot that the atoms of gas have their electrons stripped off (the atoms are ionized), and this in turn makes them susceptible to those magnetic fields. In fact, the field is coupled with the matter: the gas follows the shape of the magnetic field lines, and as the gas moves the field lines also follows the gas. As the gas churns and boils on the surface, the field lines get all tangled up. A lot of energy gets squeezed in a tight space, and when that happens the magnetic field lines can suddenly and catastrophically reconnect, releasing vast amounts of energy in a solar flare.
On December 6, 2006, a big flare detonated on the Sun. The release of energy screamed outward over the surface, expanding in a circle. Astronomers at the National Solar Observatory caught this expanding shock wave in the act:
The fuzzy white ring is the expanding wave. The scale here is numbing: the Sun is 1.7 million kilometers across, so this ring was hundreds of thousands of kilometers in diameter. Heck, just the width of the ring is far larger than the Earth!
So why is this one of my top picks for 2006? After all, the still image doesn't look like much! Ah, but the astronomers at NSO strung together a series of images into a dynamite animation. It's totally cool. I couldn't find the total energy released in this flare, but a typical big flare might blow off 1025 Joules... which is 10% of the total energy emitted by the Sun every second.
Still not sure how much that is? Think of it this way: a big hydrogen bomb might have a yield of about 1016 Joules, so this flare was the equivalent of one billion hydrogen bombs.
See why I picked this as number 3?
Number 2: Evidence of Water on Mars
Mars figured prominently in the headlines this year, and so it does here as well. This third image of the fourth rock from the Sun is my number two pick because it shows direct evidence for what might be the biggest discovery on Mars yet: the presence of recent water activity on the surface!
We know that there's water on Mars, but it's frozen. The polar caps have water ice, for example. And we see lots of evidence that water flowed billions of years ago on the surface too: there are gullies, river beds, and flow patterns of erosion. But if there's any water near the surface, it must be frozen beneath it, like a permafrost.
But we're humans, and we like our water to be liquid. Could there be any on the surface?
Recent pictures from the Mars Global Surveyor indicate that there is. It doesn't last long, and there's maybe not a huge amount of it, but it's there.
The image on the laft was taken in August 1999, and the one on the right in September 2006. The difference is obvious: the later image shows a gully filled with a lighter-toned material that was not in the earlier one (in fact, it was later seen on images from Febraury 2004). Something seeped out from below the surface and deposited that material during the intervening time. The evidence that it was water is indirect, but very compelling. Dry dust flows are generally darker, and the flow shape indicates the medium was a liquid like water.
If it was water, then there was only enough in that flow to fill a few Olympic sized swimming pools. Not enough to keep a colony drinking, but then again I wouldn't have wanted to be standing downstream when it erupted from the ground. It's a fine start.
Again, while this isn't rock-solid proof of recent water activity on the surface of Mars, it's the simplest explanation, and that is extremely exciting.
And the Number One Astronomy Picture of 2006 is...
What else could it possibly have been?
This image has it all. It's of a familiar object, seen in an unfamiliar way: back-lit by the Sun, a view impossible from Earth. It shows the whole planet, a rarity from space missions. The image shows very faint details and has very high resolution, a must.
But there is sheer artistry at work here. The colors, the lighting... I love the sun splash in the lower left limb of the planet, and the fans of ethereal mistiness shooting out from the rings. The shading on the planet itself is lovely, while the rings provide a geometric symmetry that is very appealing to the eye.
All this is necessary for the image to be the best, and together they may even be sufficient. But like all true winners, it has that extra addition, the over-the-top detail that pushes it into "all-time" status:
That dot in the center of the image is the Earth. It's us. Cassini was nearly one billion miles from us when it took this image, orbiting a giant ball of gas as exotic and alien as any place we can imagine. From such a terribly removed location, the entire Earth is reduced to a single point of light, just one among an anonymous many as seen from our robotic proxy as our generation, for the first time in all of history, seeks out our neighborhood and takes a really good look.
That's why this is the best astronomy image of 2006. And it's one of the best of all time.
Still and all, a year is a long time. In 2007 we'll see more astronomy missions launched into orbit, more telescopes built, more people than ever perusing the images from Mars, from Saturn, and from the depths of space. What portraits of the Universe will make the list next year?