2016年4月30日 星期六
Moon over Makemake
Why SLS Has Always Been About Maintaining Jobs
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No, Saturn Won’t Be Huge in the Sky on May 1
Another day, another weird Facebook astronomy hoax.
The photo with the caption above have been spread around Facebook quite a bit the past few days; it shows Saturn looming huge in the sky over a city, with the annotation, “On 5/1/16 Saturn will be the closest it ever has been to Earth. It will look like this.”
I got a few notes from readers on Twitter about it. Unlike a lot of other wrong but possibly sincere memes, this one is clearly a hoax. It’s just silly and wrong on every level, so it couldn’t possibly have just been an honest mistake. It’s a joke.
What’s wrong with it? Well, two main things: Saturn isn’t the closest it’s ever been on May 1 (its closest approach to Earth this year is in June), and Saturn can’t get big enough to look like that, ever. Which is a good thing.
The closest Saturn ever gets to Earth is about 1.2 billion kilometers. That’s something of a hike. Saturn is big — 120,000 km in diameter, not including the rings which are 250,000 km across — but from that distance it’s not even big enough to appear as a disk to the eye. Through binoculars you can see the rings as a tiny ellipse, and through a smallish ‘scope you can more clearly see the planet as a disk and the rings circling it.
To be that big, Saturn would have to get as close to us as our Moon! In fact, that’s where the image comes from. It was easy enough to track down; a reverse image search on Google showed it’s from a Russian video intended to show what the sky would look like if the Moon were replaced with the other planets in our solar system:
It’s a fanciful idea, and as far as I can tell first done by my pal Ron Miller, a space artist, in 2012, and again by videographer yeti dynamics in 2013. In fact, yeti dynamics went ever farther and created a wonderful video showing what it would look like if Saturn were actually passing the Earth in the solar system:
As I wrote at the time, that would be the most amazing sight ever witnessed… and also the last thing you’d see. From that distance, Saturn’s gravity would inflict monstrous tidal forces on the Earth, causing apocalyptic floods, massive earthquakes, and generally dealing out death on a global scale.
As much as I love looking at Saturn, I’m pretty happy it’s over a billion klicks away.
So where is Saturn right now? It’s currently about 1.37 billion km away, where it always is. It rises around 10:30 p.m. local time, and shines at a magnitude of about 0.2, making it one of the brightest objects in the sky. In fact, it’s very much worth going out and taking a look around midnight; very close to it in the sky is the much brighter and much oranger Mars, and the bright red supergiant star Antares, the heart of Scorpius. Face south and look low to the horizon for the trio; your outstretched fist can cover all three.
And if you have a telescope, well then what are you waiting for? Saturn is one of the most magnificent objects in the sky. Patience pays off, too: in early June it will be at opposition, opposite the Sun in the sky, which means it rises at sunset and it up all night. As an added bonus, that’s when it truly is closest to the Earth, and appears as big as it can. But then, that means it’ll be 0.3 arcminutes across: Only 1/100th the width of the Moon in the sky.
But through a telescope, it’s glorious. So forget the dumb Facebook hoaxes, and go see the real Universe for yourself. It’s way, way better.
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2016年4月29日 星期五
NASA Is Now Censoring Its Videos
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Fermi's Gamma-ray Moon
Future High-Resolution Imaging of Mars: Super-Res to the Rescue?
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NASA’s Juno Mission on Course for July 4 Arrival at Jupiter, Media Accreditation Open
April 29, 2016
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Sen. Mikulski, NASA Administrator Bolden to View Progress at Wallops Flight Facility
April 29, 2016
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James Webb Space Telescope's Golden Mirror
The Warped Path to Understanding the Universe
The Universe is a bit bent.
You’d think that light would travel in straight lines, going directly from point A to point B. But it’s more complicated than that. Space is curved, warped, distorted by the matter lodged within it. It’s hard for our puny three-dimensionally-adapted brains to wrap themselves around (so to speak), but what we think of as space is actually a framework that can be bent.
Mass does that bending, and we perceive that bending as gravity.
But we can see the effects of this bending, too. Like a car following a curve in the road, light follows the gravitationally induced curving of space. We poetically call this effect “gravitational lensing”, because a lens bends light as well.
Sometimes the curve in space is profound, like when a black hole makes a warp so severe it’s almost a puncture in the fabric of reality. The path a beam of light takes can be whipped around quite viciously — we call this strong lensing — or even plunge down into the black hole, never to return. Clusters of galaxies can do this as well, warping light from even more distant galaxies into bizarre shapes.
Other times that curve is more gentle, when the mass is more spread out. Individual galaxies and some galaxy clusters are like that. Instead of an obvious distortion in the direction light takes, it’s subtler, only marginally changing the light’s path.
Although harder to detect, this weak lensing can tell us a lot about the mass doing the bending of space. And that’s why astronomers used Hubble to take that lovely image of the galaxy PGC 54493 seen above.
That galaxy dominates the view, our eyes drawn to magnificent spiral arms, the bar-shaped distribution of stars in its center, the blue patches where massive stars are being born by the thousands. But it’s not the most important thing in this image.
Look around it. See all the smaller, fainter galaxies? PGC 54493 is perhaps 500 million light years or so away, but these other galaxies are much farther. The light we see from them was emitted when the Universe was far younger, and has traversed billions of light years of space to reach us.
On that trip, this light passed near PGC 54493, traveling through the region of space subtly distorted by the galaxy’s mass. The shapes of these distant galaxies thus get distorted, too, the amount of change in their shapes determined by the amount of mass in the big spiral galaxy bending space. It’s difficult to determine that for any individual faint galaxy, but if you observe enough of them, you can show statistically how much they’re warped, and therefore where the mass of the intervening galaxy lies and how much there is.
That is critical. We know that normal matter — the kind of matter that makes up you, me, the computer you read this on, and essentially every visible object in the Universe — is in the minority. Dominating the amount of matter in the cosmos is a mysterious form of it that we cannot see, but which has mass, and therefore gravity. Dark matter can’t be observed directly, but its gravity warps space, and that distorts the light from those distant galaxies, and that we can indeed measure.
Astronomers have been mapping dark matter in this way for many years; perhaps most famously in the Pandora Cluster, which showed just how dark matter in clusters of galaxies can affect the light from more distant galaxies. They continue to observe other clusters to make even more maps of the distribution of dark matter in the Universe, and that’s why PGC 54493 was the target of these observations.
Although bright and beautiful, it’s the dark reach of that galaxy that concerns us, invisible matter making invisible bends in space, distorting more distant galaxies in almost, but not quite, invisible ways.
Sometimes the Universe is obvious, ostentatious, perhaps even gaudy. But other times it whispers, hints at us to follow the rules of math and science that shape it, and in so many cases it is following that path — distorted and subtle as it may be — that leads to seeing its underlying structures.
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ISS Daily Summary Report – 04/28/16
April 29, 2016 at 01:33AM
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2016年4月28日 星期四
NASA Hypes Its Imaginary Plan for the #JourneyToMars
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A Dust Angel Nebula
Changing The Way We Explore Space
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NASA Dedicates Facility to Mathematician, Presidential Medal Winner
April 28, 2016
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What NASA Can Learn from SpaceX
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ULA Struggles With Old Engines and New Business Realities
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Orion Crew Module for Exploration Mission-1 Lifted to Test Stand
The phases of the far side of the Moon
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ISS Daily Summary Report – 04/27/16
April 28, 2016 at 12:44AM
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Climate Change Is Strangling Our Oceans
As our globe heats up, the effects of those rising temperatures are complex and varied.
Overall, we call these effects “climate change”, but that’s an umbrella phrase that covers a vast number of changes. Melting polar ice, glacial melt, changing weather patterns, more extreme weather, rising sea levels, ocean acidification… these are the topics we hear about quite a bit. But there are other changes going on, and these are every bit as much a cause for concern.
For example, global warming is strangling our oceans.
By that I mean that oxygen levels in the oceans are affected by global warming, too. This occurs in two general ways. One is that warmer water has a harder time holding on to dissolved gases — that’s a basic law of chemistry. So oxygen levels drop as water warms. The other is that as surface waters warm, they expand, and mix less with deeper water. Surface water gets most of its oxygen from phytoplankton that breathe it out. That water sinks, and mixes with deeper water. As the water becomes more stratified due to global warming, less of that oxygenated water gets to lower depths.
The question then becomes, when will we start to see the effects of global warming on the oceans’ oxygen content? Like so many other aspects of climate change, we’re seeing that deoxygenation due to human-generated global warming occurring now. Not sometime in the distant future. Now.
That’s the result of a new study done by a team of scientists led by Matthew Long, an oceanographer at the National Center for Atmospheric Research in Boulder, Colorado. He and his fellow scientists used a sophisticated computer model that calculates the amount of oxygen dissolved in the oceans over the globe and with ocean depth. The model accounts for a great number of factors, including air temperatures, water temperatures, layers in the water, sea ice, and much more.
Global warming changes the air temperature, which affects the model. In the past, global warming was small, and natural variations in the environment change the oxygen levels far more than human-made warming. But, as the world warms more and more, the effect of warming increases, and at some point becomes noticeable over the natural variations.
Think of it this way: Imagine being in a loud room, with many people talking, and someone nearby whispers at you. You can’t hear them at first over the ambient noise, but if they keep speaking more and more loudly, at some point you can distinguish their voice from the crowd.
The scientists running the model wanted to know when they could hear the voice of warming over the babble of the natural variations. They ran the model many times, varying the air temperature a small amount with each run. This gave them a range of outcomes that they could compare to physical measurements; that gave them a check to make sure they had real-world testable outcomes.
What they found is sobering. Deoxygenation due to human-made global warming is already detectable in the southern Indian Ocean, and in some regions in the eastern tropical Pacific and Atlantic. By 2030 to 2040 — two decades from now — they expect to see more and more widespread deoxygenation over the globe. By the year 2100 (which is how far into the future they ran the models) a significant fraction of the global oceans will see some deoxygenation due to human activity.
This is, obviously, bad. The amount of deoxygenation may not be very much, just a drop of a few percent. But as we learned with increasing carbon dioxide levels in the atmosphere, and rising temperatures, it doesn’t take much change to destabilize a system.
The worst effects will come from areas already low in oxygen, called hypoxic zones, where the levels can be as much as 70-90 percent lower than average, and in suboxic zones, where it’s even lower. In those regions, a few percent drop can mean the difference between life barely holding on, and death.
Even when the change isn’t so dramatic, it can be devastating. You might think of the ocean as one big fish tank, but it’s actually incredibly diverse, depending on water temperatures, currents, pressure, and more. Changes in oxygen levels in the water reduce marine life habitats, stressing the inhabitants there. Changes in regional oxygen levels have caused migrations of fish, and even massive die-offs. Besides the effect on the life there, this has an impact on human activity including fishing, on which many countries depend.
Mind you, about half the oxygen we breathe comes from ocean phytoplankton. Messing with their habitat is like setting fire to your own house. Which is pretty much what we’re doing.
So you can add this to the list of deleterious effects of global warming to our planet. And don’t forget that the past six months have all had record-breaking high temperatures, with many scientists already expecting 2016 to be the hottest year on record globally, and carbon dioxide levels still rising.
Global warming is our future, but it’s also our present. It’s now. Once again, Americans, I implore you to consider this, what is perhaps the greatest long-term threat facing humanity, when you go to the voting booth in November. And for the rest of the world, know that most of us here in the US are aware of the problem and doing our best to urge our leaders to take action as well. We can minimize the damage of global warming, but first we have to make sure our government is facing reality.
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Shuttle tank, meet canal: Engineering wonders cross paths in Panama
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2016年4月27日 星期三
Omega Centauri: The Brightest Globular Star Cluster
Putin Wants To Jail Spaceport Employees
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NASA Awards Academic Mission Services Contract
April 27, 2016
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NASA Selects American Small Business, Research Institution Projects for Further Development
April 27, 2016
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Full-Circle Vista from 'Naukluft Plateau' on Mars
SpaceX Will Go To Mars Starting in 2018
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A Moon for Makemake
Well now, this is very cool: Astronomers have just announced that Makemake has a moon!
Makemake (pronounced MAH-kay-mah-kay; it’s named after a Rapa Nui god who created humanity) is a Kuiper Belt Object (or KBO), a large icy world orbiting the Sun way out past Neptune. It’s what’s called a “classical” KBO, because its orbit is far enough from Neptune’s that it can orbit the Sun stably for billions of years (Pluto actually gets closer to the Sun than Neptune does, but their orbits are timed such that they never get very close together). At 1430 km across, it’s the biggest known classical KBO, and the third biggest such body known past Neptune. Only Pluto and Eris are bigger.
We know quite a bit about Makemake from previous observations. It takes about 7.77 hours to rotate once, and must have a very reflective surface. Spectra show it has a lot of frozen methane on it, too, more than any other object out past Neptune. Its orbit is elliptical, taking it as close to the Sun as 5.8 billion km and as far as 7.9 billion km out. Right now it’s almost at aphelion, the point in its orbit when it’s farthest from the Sun.
It’s been observed many times, but until now no moon had been found. The discovery was made using Hubble Space Telescope, which observed Makemake exactly one year ago, on Apr. 27, 2015. The moon — which for now has the cumbersome designation S/2015 (136472) 1 — was seen very close to the KBO, almost lost in its glare.
That may be why it hasn’t been seen before. For one thing, it’s much fainter than Makemake, making it hard to detect. The astronomers who discovered it also propose that we may be seeing its orbit edge-on, which means it spends much of its time too close to Makemake to easily detect from Earth.
The observations were split into two “visits”; one on Apr. 27 and the next on the 29th. The moon was seen in the first visit but not the second, meaning it was too close to Makemake to see in the second set. Each visit consisted of six long exposures, and the moon was seen in all six images on the first visit.
The problem is, the time between the first and last images in the first visit was only a couple of hours, which was not enough to show any motion of the moon. That means the orbit isn’t well known. The best the astronomers could do was say that the orbital distance is at least 21,000 km, but may be as much as 300,000! For comparison, the Moon orbits the Earth at a distance of about 380,000 km. The moon orbits Makemake with a period somewhere between 12 and 660 days.
Those are pretty wide ranges. And that’s too bad, because the orbit of a moon is really critical: It tells you the mass of the object it orbits. Gravity depends on mass of the primary object and the distance to the moon, so if the orbital period of S/2015 (136472) 1 had been measured, the mass of Makemake could have been found.
What makes this even more frustrating is that we know how big Makemake is, because in 2011 it passed directly in front of a star as seen from Earth; the length of time it blocked the star combined with its known orbital speed yielded the diameter of 1430 km. With that number, plus the mass, its density could be determined, and that gives a huge clue about what it’s made of. Rock is denser than ice, for example, so just knowing Makemake’s density would constrain its composition.
However, the good news is that now that we know the moon exists, more observations can be made. It may take Hubble to see it once again — Hubble’s really good at spotting faint things near bright things — but it can be done. And if carefully planned (which it will be) the moon’s orbital period and shape can be found.
There are some interesting implications of this, too. Earlier infrared observations of Makemake indicated the surface had at least two different materials on it, which had different thermal properties (darker material, for example, gets warmer than more reflective stuff). If that were the case, though, the brightness of Makemake should change enough to measure as it spins, but no such change was seen.
The moon may solve this problem! If it’s darker than Makemake then that would throw off the infrared observations. Those telescopes couldn’t separate the moon and the KBO, so they merged together, confusing the interpretation.
I find that very interesting indeed. As you may remember from last year, Charon, Pluto’s moon, is much darker than Pluto as well. If this new moon is indeed dark, that might indicate a similar origin story. Future observations with the James Webb Space Telescope, due to launch in 2018, may help figure this all out; it has the keen vision in the infrared to separate the two objects and determine how reflective the moon is.
Just the fact that the moon exists is interesting, too. Pluto has a moon, as does Eris and Haumea (another large trans-Neptunian object a bit smaller than Makemake). Are they ubiquitous? Two other such objects, Sedna and 2010 OR10, have no known moons. Perhaps we just haven’t seen them because they’re too close to their primaries. Clearly, more and deeper observations are needed.
And let’s not lose sight of the more general nature of this: We’re still learning basic information about our solar system! Finding a moon like this gives precious insight into what the outskirts of our celestial neighborhood are like, a region that is terribly far away and dark, and very difficult to explore. Each discovery about it is a clue to how it came to be, how it changed over time, and why it looks the way it does now.
All of this tells us more about our existence, and informs us about our own world. A cold and distant moon orbiting a smallish iceball may not seem like much, but it’s another piece of the puzzle, one worth investigating and understanding.
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2016年4月26日 星期二
NGC 6872: A Stretched Spiral Galaxy
Some - But Not All - Politics Is Good For NASA
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ISS Daily Summary Report – 04/26/16
April 27, 2016 at 01:07AM
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The Senate Just Proposed to Slash Planetary Science Funding
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Charlie Bolden Is Very Confused These Days
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Light Echoes Used to Study Protoplanetary Disks
Field Report From Mars: Sol 4333 - April 1, 2016
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An Emerald Green Comet and a Billion Stars
I’ve said many times that there are no green stars, but that doesn’t mean there are no green objects in space.
My pal Babak Tafreshi makes this point beautifully in his phenomenal photograph of the night sky over the Paranal Observatory in Chile:
Oh my. Isn’t that gorgeous? In the foreground is one of the four smaller auxiliary telescopes that make up the Very Large Telescope Interferometer, a sophisticated piece of equipment that can take observations with far higher resolution even than Hubble. And by smaller, it’s a 1.8-meter wide mirror; that’s only small when compared to the 8.2 meter behemoths that make up the Very Large Telescope!
But that sky. To the right of the telescope blazes the billions of stars of Milky Way, our home galaxy, partially obscured by dark dust lanes and punctuated by the pink glow of hydrogen in the Lagoon Nebula.
But that green fuzzy glow above the telescope somehow manages to steal the show, perhaps because its color makes it stand out in stark contrast to the other objects in the sky. That emerald blob is the comet 252P/LINEAR, which passed the Earth in mid-March at a close distance of more than 5 million kilometers.
Many comets glow green; it’s due to the presence of a molecule made of two carbon atoms (C2), so that’s not a big surprise. But that’s about the only nonweird thing about 252P.
It turns out it was full of surprises. For one thing, it was followed closely by another comet, P/2016 BA 14, which had a very similar orbit, sparking hypotheses that they were once the same object that split. Both passed very close to Earth (the fourth and seventh closest passes of comets in recorded history).
This gave astronomers a chance to observe BA 14 with radar and lead to another surprise: BA 14 was way bigger than first thought. From its brightness it was at first estimated to be less than 200 meters across, and probably much less. But the radar observations showed it was more like a kilometer across! It turns out the solid nucleus of BA 14 is incredibly dark, reflecting less than 3 percent of the light that hits it. That makes it fainter than expected, which is why astronomers thought it was small.
Around the same time, 252P had a huge outburst, suddenly becoming 100 times brighter in a short period of time. It went from obscurity to becoming naked-eye visible, though unfortunately for us in the Northern Hemisphere it was too far south to see. But that was good news for Babak, who was able to capture it in the photo above while he was visiting the European Southern Observatory facilities.
It’s rare, but sometimes comets flare in brightness. This can happen if they clave (split off a piece), which can release a lot of ice that turns into gas; that reflects sunlight and makes the comet brighten. In 2007 Comet Holmes underwent a tremendous outburst that made it easily visible to the naked eye even though it was out past Mars; it’s brightness increased by a factor of a million! I was fortunate to be in a place where I could see it, and it showed a disk easily to the naked eye; the cloud was more than 1 million kilometers across. I’ve never seen anything like that before, nor since.
Which goes to show you, it always pays to keep your eyes on comets. Sometimes they fizzle, but when they perform, they can really perform, and all the time spent watching them can suddenly pay off.
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Vector Launch Systems Enters Microsat Launch Business
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2016年4月25日 星期一
America's Hypocritical Fear of Indian Rockets
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NASA Created OpenStack, Dumped It, And Now Re-Embraces It
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Simeis 147: Supernova Remnant
The RD-180 Food Fight Just Got Crazier
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Quick Curiosity update, sol 1320: "Lubango," the 10th drill site on Mars
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Five Days in Paradise: Come to Science Luau 2016
Aloha! I’m pleased to announce registration is open for Science Luau 2016, a five-day vacation on the Big Island of Hawaii, with a special bonus: SCIENCE.
My wife and I run a company called Science Getaways, where we take people on vacations that are already really nice and add science to them. For this trip, we’re spending Sep. 19–23 on the Big Island, in the lovely and luxurious Mauna Lani hotel on the Kohala coast.
We have several special extras planned. We’ll take a trip to the Kilauea volcano with an expert tour guide, ending in a stop at dusk at the summit crater, Halema'uma'u (ha-LAY-mah-oo-mah-oo), to see the lava pool glowing and illuminating the sulfur plume huffing and puffing out of it. We’ve chartered a boat to go to some coral reefs for snorkeling, and then we’ll go night diving with manta rays. We’ll also be taking a hike through a dry forest with another expert guide to look at the amazing native Hawaiian trees and wildlife.
I know a thing or two about astronomy, so I’ll be bringing my solar telescope to show you what our active Sun is doing that week. On top of all that, there will be talks by experts about what we’ll be experiencing; I’ll be giving an astronomy talk as well.
We’ve been doing these Getaways for a few years now, and they have always been a lot of fun, with honestly wonderful people (many have made lifelong friends on these trips). We went to the Big Island last year and it was so popular we decided to do it again.
I hope you’ll join us. All the information you need is on the Science Getaways page. Mahalo, and see you in paradise in September!
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NASA Puts Dallas Students on Phone with Orbiting Astronauts
April 25, 2016
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Ice Scours the North Caspian Sea
A Martian Crater Torn in Half
Sometimes geologists have it easy.
In astronomy, you can have two stars right next to each other, maybe even born in the same cluster, but you can’t be sure they’re the same age, or which one is older than the other. Differences can be really subtle, and have to be teased out of the data.
Geologists, on the other hand, get stuff like this:
WOW. That is a scene on Mars, taken by the wonderful HiRISE camera on the Mars Reconnaissance Orbiter. Its shows a small portion of Ganges Chasma, a huge, sprawling channel cut into the surface of Mars, probably due to catastrophic flooding a billion or more years ago. The violent rush of water cut through the landscape like God’s trowel, carving out the chasm.
Over time, erosion, weakness in the walls, or subsequent floods would have caused the walls to collapse inward further. Eventually, though, all that stopped, leaving behind the tableau we see now.
In the shot above, a crater about 3.5 kilometers (2.2 miles) across had the misfortune to be too near the flood. The surface just south of it collapsed, slicing the crater nearly in half.
But this is good fortune to Terran geologists! The crater was obviously there first, sitting in the surface from some ancient impact, minding its own business when the world collapsed next to it. The edge of the crater over the canyon is clean and sharp, and the crater itself quite nicely formed. If the crater had occurred after the flood, the shape would be distorted by the edge of the canyon.
The crater itself is interesting. It’s terraced, with circular ledges inside the main rim. Quite a few of these are seen on Mars. This can happen when there’s a layer of material under the surface with a different strength, like ice under rock. The shock wave from the impact carves out the main crater, then slams into the layer underneath and creates a smaller crater inside the first one. There are also smaller craters dotting the interior, and you can even see rippling sand dunes in the upper left of the floor.
Speaking of layers under the surface, using Google Mars to get some context, you can really see more of what happened after the channel formed:
The crater is arrowed. Note the weird raised features in the canyon floor; those are likely muddy or possibly dry material flows that happened when sections of the canyon wall collapsed. These landslides can create scalloplike indentations in the wall; many of them look like impact craters. But the featured crater here is clearly from an older impact.
One more thing: HiRISE takes multiple images as it sails over features, which means 3-D anaglyphs can be made. Got red-green or red-blue glasses? Check this out!
Yegads. That really drives home the size and scale of this catastrophe.
Not that this in any way makes me less jealous of geologists, who sometimes have the timeline of events spelled out right in front of them. It’s a little ironic. Studying Mars used to be astronomy, and in some ways it still is. But now we go there, now we explore it, now we send robots to the surface to drill into it and zap it with lasers and sift through the dust to determine what it’s made of and what its history is.
Mars used to be astronomy, but now it’s a world, a place. Handing over the keys to the planet to geologists is hard, but oh, it’s so rewarding.
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2016年4月24日 星期日
M16: Pillars of Star Creation
A Twice-Lit Moon Kisses the Horizon
Sometime you see a photograph that’s just so wonderful you can’t wait to show it to other people.
That shot above is one of those photos.
It was taken by Petr Horálek, a European Southern Observatory Ambassador — the Ambassadors are a group of excellent photographers who shoot pictures of the ESO observatories for public outreach.
The photo was taken on April 6, 2016, just minutes before sunrise. Smack dab in the center is Venus, cruel twin of the Earth, covered in clouds so reflective they make the planet the third brightest natural object in our skies.
Below it is the crescent Moon, less than a day before its new phase. The crescent is so thin it’s almost an afterthought. Amazingly, the rest of the Moon’s surface was unlit by the Sun. So why can we see it? Earthshine! Light from the Sun hits the Earth, reflects off of it, illuminating the Moon, which then reflects it back into space, and to Earth. Our planet is very bright in the lunar skies, 50 times brighter than a full Moon. That’s enough to softly bathe the surface of our satellite in light.
Note too the Moon looks a little squished. That’s an effect of our atmosphere, which curves along with the Earth’s surface. Near the horizon, the light from the bottom of the Moon goes through a thicker layer of air than the top part of the Moon. The air acts like a lens, bending that light, making the Moon look flat.
Horálek timed this photo perfectly, getting the shot just as the Moon cleared the distant mountains. Had he waited much longer the Sun would have lit things up too much anyway. This was a time exposure, too: You can see the faint stars of Pisces surrounding the Moon and Venus.
And let’s not ignore the foreground! The silhouetted dome houses the 1.2 meter VLT Auxiliary Telescope, part of the Very Large Telescope array. See the two people crouched nearby? That’s my friend Babak Tafreshi on the left and Yuri Beletsky on the right, wrapping things up after a long night of photography in the incredibly rich and dark skies of this remote location in the high desert of Chile. I’ve featured both their works on this blog many times; click their names to fill your eyes and brain with delight.
I dream of capturing a photograph like this some day. But I just dabble in this; Horálek, Babak, and Beletsky are professionals. I might feel a pang of jealousy seeing shots like this, but it evaporates rapidly as I take in the sheer beauty. I’m glad there are so many people out their willing to collect the few photons the Universe graces us with, and share them with the world.
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2016年4月23日 星期六
Milky Way in Moonlight
First astronaut to run a marathon in space
The Telegraph (UK), ITV News (UK) and the Courier Mail (Australia) all seem to think that Tim Peake will be the "first person" to do this during tomorrow's London Marathon.
ITV News incorrectly claims "Tim Peake will become the first ever person to take on a marathon while in space"
Given their publication dates of these stories, I imagine that they read the Principia Mission blog, saw "Tim Peake will become the first man to run a marathon in space", and didn't appreciate that "man" was a very necessary qualifier to the statement. Converting "first man" to "first person" may be due to an unconscious assumption that men set records first. It also suggests that these stories were written by people who didn't have any relevant background knowledge or time for basic fact checking.
US news outlets (including the Washington Post and Fox News) have remembered that Sunita Williams already did a marathon. Hopefully that isn't just because she is American.
Good luck to Tim for the London marathon tomorrow morning. He could break Sunita Williams' current record for completing a marathon in space.
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Valley of the Cosmos
Photographer Michael Shainblum is a wonder. His photographs are just stunning, one after another. I’ve been following his work for years, and every time he posts something it’s awe-inspiring.
Oh, you want an example? Then how about this for your eyeballs?
He titled that one “Valley of the Cosmos”, which is pretty much on the button. The “valley” in this case is Yosemite Valley — see Half Dome in the center? — and the “cosmos” bit is obvious enough.
… or is it? In this view, a panorama, the Milky Way spans the frame. Our galaxy is a thick disk, and we’re inside it, so we see it as a broad splash across the sky. The central region bulges outward, and that can be seen off to the right. The colors are interesting; probably not what your eye would see, but that happens when the contrast is stretched in a photo when you’re trying to bring out faint details. Still, very pretty.
The orange glow is from humans; the horizon commonly shows light pollution from towns sometimes hundreds of kilometers away (Fresno is only about 100 km south of Half Dome).
But what the heck is that green glow? You might guess it’s the aurora — a few people on Facebook did think that, in fact, when he posted the picture — but it’s not; Shainblum was facing south when he took this shot, not north.
That emerald radiance is actually airglow. During the day, sunlight hits atoms and molecules in the upper atmosphere, 100 km above the Earth’s surface. The energy can be stored, then released slowly at night in a process called chemoluminescence. Green is a strongly favored color due to oxygen atoms (similar to why many aurorae are green).
And the ripples? Even at that height, the air is subject to wind and flows. Those ripples are called “gravity waves” (not to be confused with gravitational waves), which I’ve written about before:
The rippling is due to gravity waves. This is simply an up-and-down oscillation of something under the influence of gravity. For example, waves on the surface of the water in your bathtub are gravity waves; the water gets pushed up a little bit (maybe when you plop your rubber ducky into the water), and then gravity pulls that crest of water back down. But the water itself pushes back, and you get oscillatory motion.
This can happen in air, too (air is a fluid, after all). Currents of air in the upper atmosphere bob up and down pretty often, similar to the water in your tub. This motion can disturb the process that creates airglow, so you get those rippling waves moving across the sky.
I love how perspective makes those parallel ripples in Shainblum’s photo appear to converge on the horizon, right behind Half Dome! You couldn’t hope for a better bit of placement.
More of Shainblum’s photography can be found on his website, on 500px, on Facebook, and on Instagram. Treat yourself, and go take a look. Everyone could use a little more beauty in their world.
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2016年4月22日 星期五
NGC 7635: The Bubble Nebula
What Will The NASA Budget Look Like? Just Follow The Money
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How The #JourneyToMars Becomes The #JourneyToNowhere
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NASA Space Apps Challenge: Women hacking space image data
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Sometimes NASA Goes Too Far With The Whole Green Thing
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Morning Sunglint Over the Pacific
Noon on a Comet
A couple of weeks ago I posted a dramatic shot of the comet 67P/Churyumov-Gerasimenko backlit by the Sun, taken by the Rosetta spacecraft from a distance of a few hundred kilometers. I mentioned how the spacecraft was on a long looping path that would soon take it back to the comet, passing directly between it and the Sun at a distance of about 30 km, which should make for some very pretty pictures.
Well, here you go: As promised, the image above shows that exact event! Rosetta was 29.9 kilometers above the surface of 67P when it took that shot on April 12, 2016, using the OSIRIS wide-angle camera. As you can see, shadows are nearly non-existent, and only appear where there’s a sudden change in the topography of the comet (cliffs, shelves, and the like) near the edge of the comet.
And that glowing spot left of center is real, too! There are lots of fancy names for it, including the zero phase effect and heiligenschein, but I think my favorite is “opposition surge”. Poetic and scientific, all at the same time.
There are two reasons for it. One is that from the spacecraft’s view, the Sun is directly behind it, so the Sun’s light is shining straight down on the comet. At that spot directly below the spacecraft you don’t see shadows, so the surface looks brighter. Not only that, but some types of terrain bounce sunlight straight back in the direction it came. If you’re on that line, you see that spot on the ground being brighter than the area around it.
The Sun is in the opposite side of the sky as that spot, hence the term “opposition”, and the surge is pretty obvious. Heiligenschein means “halo” in German, and if you’ve ever seen a faint glow around the shadow of your head as walk past a patch of dewy grass, you’ll understand that term, too.
As for zero phase, the technical term for the angle between the source of light, the observer, and the spot illuminated is the “phase angle”. When they’re all on a line that’s defined as zero. The term should actually be familiar to you in another guise: The angle between the Sun, you, and the Moon defines the Moon’s phase! Surprise! You know more technical stuff than you probably thought.
By the way, the Rosetta shot is looking up at the flattish “underside” of the comet, the broad region across the wider of the two lobes making up 67P’s rubber ducky shape. You can see part of the smaller lobe, the “head” on the left. The shape looks funny when shadows go away; it’s hard to tell what’s what. Shadows actually help us understand the terrain, and can be used to make 3D maps of the surface. But this zero phase angle helps too; the surge can be used to understand better the surface on much smaller scales; different sized grains of ice or other materials change the brightness of the surge.
Fantastic! Science and geometry come together to form beauty. As they often do.
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ISS Daily Summary Report 04/21/16
April 22, 2016 at 01:06AM
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Understanding What NASA's FY 2017 Budget Numbers Really Mean
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Sometimes It Is Purple in Space #Prince
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Planetary Society solar sails paved way for Alpha Centauri starshot
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2016年4月21日 星期四
The Comet the Owl and the Galaxy
NASA Astronaut Kjell Lindgren Visits Washington April 25-29
April 21, 2016
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NASA Seeks Industry Ideas for an Advanced Mars Satellite
April 21, 2016
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A Seriously MASSIVE Bubble Blown in Space Celebrates Hubbles 26th Anniversary
On April 24, 1990, the Hubble Space Telescope was lofted into orbit onboard the Space Shuttle Discovery. Sunday is the 26th anniversary of this grand event, and to celebrate, the good folks at the Space Telescope Science Institute have created a new and simply spectacular image.
Get a load of this!
That is the Bubble Nebula, aka NGC 7635. It looks almost delicate, doesn’t it? Like a thin soap bubble floating in space.
But that's a lie. Nothing about this tremendous beast is delicate.
What you’re seeing is the gas blowing outward from a massive star. Called SAO 20575, it’s the brightest star in the image, near the left edge of the bubble. And by massive, I mean somewhere between 10 and 40 times the mass of the Sun, so it’s a real bruiser. It’s already used up all the hydrogen in its core and is fusing heavier elements to generate energy. The vast amounts of energy generated in the core when this happens heats the outer layers so much that they get blown away from the star, forming the nebula.
The star is incredibly bright; it emits something like 400,000 times as much energy as the Sun does! If you replaced the Sun with SAO 20575, we’d have about one second before regretting that decision. The Earth would be cooked. Good thing SAO 20575 is 8,000 light-years away.
Because the wind is so fiercely powerful, the nebula itself is huge. When a star like the Sun dies and blows a similar (but far less energetic) wind, the nebula it makes might be one or two light-years across. Because the distance isn't well constrained, the exact size of the Bubble Nebula isn't well known, but measured from Hubble images it's something like five to eight light-years in diameter. That’s 50–80 trillion kilometers across! Put simply, that’s ridiculously big.
The Bubble really is a bubble, too: The wind blows away in a sphere, but winds up being bright around the edge because of an effect called edge brightening; when we look at the nebula, we see more material near the edge than when looking through the middle, making the edge look brighter. This can be reinforced if the nebula is expanding into gas that was previously outside the star; the material gets snowplowed up, adding its own brightness to the nebula’s.
You may have noticed the star blowing the bubble is way off-center, far to the left. That can happen if the star is moving rapidly in space, so fast it moves away from the center of the nebula it blew. The star’s motion has been measured and is in the right direction to account for this.
There’s also another possibility. The interstellar material surrounding the bubble is pretty thick; massive stars don’t live long and don’t usually get very far from the cloud of dust and gas from which they were born. The star is so bright that its ultraviolet light is evaporating that material, which is thickest to the upper left as seen in this image. That created a density gradient in the gas, a change in its density from one side to the other. If that’s the case, than the wind from the star can expand more easily in the direction away from the denser gas, making the bubble off-center from the star.
If that’s the case the Bubble may not actually be spherical; we just happen to see it looking down its elongated axis (that’s the case for the famous Ring Nebula, which looks round but is actually more barrel-shaped).
There is still some uncertainty about how this object was sculpted in this way. We’re still learning about it. The Bubble was observed before by Hubble, in 1998 and in 1999, the best images ever taken at the time, and you can see how much clearer our view is now.
And I can’t think of a more fitting tribute to Hubble itself. Launched more than a quarter century ago, it’s opened up so much of the sky to us, and brought the beauty of the heavens to humanity in a way never done before. Over time it’s been upgraded, with new and more powerful cameras installed, sharpening our view and our understanding of the cosmos.
And it’s not done yet. There’s still so much to see, so much to learn. Hubble has brought us a long way, but—happily—this is a journey that never ends.
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Moonset over Mars
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