2014年12月31日 星期三
Comet Lovejoy before a Globular Star Cluster
Riding With Cassini Through 2014
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A Look Back at an Amazing Year
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NASA Highlights Astrophysics Discoveries at American Astronomical Society Meeting
December 31, 2014
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Planetary exploration in 2015: The Year of the Dwarf Planet
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Hubble Sees an Ancient Globular Cluster
2014年12月30日 星期二
Observatory, Mountains, Universe
James Hsiu-Kai Chi
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Curiosity results from AGU: Methane is there, and it's variable
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Why Does NASA.gov Ignore Cool ISS Photos?
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Field Report from Mars: Sol 3875 – December 18, 2014
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Space Simulation Chamber Prepared for Testing Webb Telescope
2014年12月29日 星期一
The Sun in X rays from NuSTAR
Virgin Galactic at ISPCS
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CIA Admits That It Owns All of the Flying Saucers
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New camera improves a California near-Earth asteroid program
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NASA Updates Pre-Launch Briefings for Upcoming Resupply Mission to Space Station
December 29, 2014
from NASA http://www.nasa.gov/press/2014/december/nasa-updates-pre-launch-briefings-for-upcoming-resupply-mission-to-space-station
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Dawn Journal: History of Ceres
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View of the Alps From Space
Bigelow in 2015
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Pope Francis to Earth's Catholics: Take Action on Global Warming
In a few weeks, Pope Francis will visit the Philippine city of Tacloban, which was devastated by Supertyphoon Haiyan in 2012. Shortly thereafter, according to the Guardian, he is expected to present an encyclical on climate change, “urging all Catholics to take action on moral and scientific grounds.”
Wow. And no sarcasm there; I mean it. Wow.
This is a very big deal, for many reasons. One is that encyclicals are published on issues of high priority to the Pope, and what’s high priority to him is high priority to the Church. There are over a billion Catholics on the planet, so this could have a profound effect.
Another reason is that, also according to the Guardian article, he is doing this to directly affect the outcome of a very important meeting late in 2015: The United Nations Framework Convention on Climate Change will meet, and their express intent is to create a legally binding global agreement about actions to take on climate change.
I find this to be very good news. High profile figures speaking up about our ever-warming world will go a long way toward taking the action we so very desperately need to take.
In many countries, where Catholics have a strong political presence, this encyclical is bound to have a positive effect. In the US… well, James Inhofe (R-Oklahoma) is arguably the most powerful climate change denier in politics, and he’s a Presbyterian. Inhofe says climate change is a hoax, and that humans can’t possibly affect the environment because God “is still up there”. I suspect he is unlikely to be swayed by the Pope, and is actually far more likely to dig his heels in (and bury his head in the sand) even more.
The basic problem here, the very basic problem, is that arguing over climate change isn’t based on science, it’s based on ideology. The facts are overwhelmingly clear that the globe is warming, creating catastrophic effects from pole to pole, and people who deny that are shutting their eyes tightly and sticking their fingers in their ears.
However, I have hope. Pope Francis choosing to do this after visiting Tacloban is wise; people there are still recovering from the incredible power of Supertyphoon Haiyan… and it’s known that cyclones like that one are becoming more powerful due to global warming. It will present a strong and clear message of the urgency of this issue.
What does it say to you that one of the most socially and politically conservative organizations on the planet is saying it’s time to take action about global warming?
I have no doubt that the deniers in Congress (and in the usual venues) will bloviate, creating sound and fury over this. But what they are doing is flailing, trying to delay the inevitable.
We are not in a position to delay any longer. The effects of global warming are profound and dangerous, threatening our civilization. And they’re happening now. Not in some nebulous future. Now.
In many ways, this Pope has proven to be very forward-thinking. I welcome his words to take action.
from Bad Astronomy http://www.slate.com/blogs/bad_astronomy/2014/12/29/pope_francis_pontiff_will_issue_global_warming_encyclical.html
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2014年12月28日 星期日
Unusual Light Pillars over Latvia
The 4th MSL Landing Site Workshop: Day 2 - Eberswalde
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Fake New Year 2015
Not the view at midnight. CREDIT: NASA/NOAA
Ways to tell this pictures isn't what it claims:
- Time zones - The image covers over 4 time zones so "Europe" has midnight at different times not all at once.
- No clouds - The entire continent is rarely free of cloud, particularly in winter.
- Ireland - Ireland doesn't just have red fireworks.
- Fireworks at sea? - Highly-flammable North Sea oil rigs aren't the best setting for massive fireworks displays.
Although the image is not New Year's Eve, it does show something pretty interesting. It is a mosaic made by the US's National Oceanic and Atmospheric Administration showing lighting changes between 1993 and 2003. The red areas are lights that are new in that period, blue areas are those that have reduced, and orange and; yellow are areas of high intensity lighting that have got brighter.
Footnote: this post is a cut down version of my posts from 2014 and 2013. - taken from Astronomy Blog (http://www.strudel.org.uk/blog/astro/)
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An Accidental Eclipse from 700 Million Kilometers Away
Astronomers keeping an eye on Jupiter’s moon Io got a surprise on Dec. 16 when it looked like something had taken a bite out of it:
What they saw was another of Jupiter’s moons, Europa, passing directly in front of Io, what astronomers call a transit (or more generically a “mutual event”).
Jupiter’s moons orbit the giant planet directly above its equator, and a few times a year everything lines up just right so that, from Earth, we see the orbits edge-on. When that happens the moons can pass in front of each other, creating a transit (or an eclipse if the more distant moon is completely (or nearly completely) covered).
I had to laugh when I saw the animation. My first thought was, why didn’t the astronomers know this would happen? The log records (in the link above) show they really were surprised. So I looked up how often these transits happen, and it turns out to be a little complicated. First, they happen clustered in time when Earth passes through Jupiter’s equatorial plane. Then you might only see a half dozen or so from a given location per month (some happen during the day, or behind Jupiter, when you can’t see them). That’s not very many, and even then they only last for a few minutes at a time.
So really, from a given observatory, it’s pretty unlikely at any given time to accidentally observe a transit. However, in this case, astronomers are engaging in a long-term campaign to observe Io, because the tides from Jupiter cause it to be the most volcanically active object in the solar system. Its volcanoes are constantly erupting, and when they do they’re visible in the infrared. The Gemini telescope, which made these observations, is designed to look at these wavelengths, and in fact you can see an active volcano on the upper left part of Io’s face. Since things on Io change all the time, lots of observations are made, and so it’s inevitable a visible transit would happen eventually.
Europa’s surface is water ice, which is pretty good at absorbing the particular color of infrared observed, so it looks dark. After the transit, the astronomers switched filters so that Europa can be dimly seen moving off to the upper right.
Sometimes there can be serendipitous science from such things; for example, the exact timing can be used to test equations predicting locations of volcanoes on Io and the positions of the moons themselves.
But one thing that I’m pretty sure will come of all this: In the future, I bet the astronomers making these observations will check for mutual events before the observations start!
from Bad Astronomy http://www.slate.com/blogs/bad_astronomy/2014/12/28/io_europa_eclipse_mutual_event_caught_by_gemini.html
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2014年12月27日 星期六
The Winter Shower
A Tiny, Faint, Ancient Neighbor
One of the problems with astronomy is best portrayed by an old joke: At night, a cop notices a kid under a street light, looking intently all around him. The cop walks over and asks, “What are you doing, son?” The kid responds, “I lost a dollar, and I’m looking for it.”
The cop looks around for a moment, then asks, “Well, where did you lose it?”
The kid points over to a dark spot across the street. “Over there.”
“Well then, why are you looking over here?” the cop responds, reasonably.
The kid shrugs his shoulders. “The light’s better here.”
Such is astronomy. It’s easy to find the bright stuff, but the fainter objects are tougher, and we sometimes forget about them.
But they’re important. And that’s why the discovery of KKs 3 is so interesting: It’s a dinky spheroidal dwarf galaxy, thought to be the basic building blocks of much beefier galaxies like our Milky Way. Fewer than two dozen are known, so every new one is a gift.
KKS 3 is located about seven million light years away, which is pretty close by—just across the street, so to speak. But it’s fairly isolated, too. The Milky Way is part of a small clump of galaxies called the Local Group, and along with the Andromeda spiral galaxy we’re the two biggest. Most are small dwarf galaxies, and we’re all clustered into a volume of space roughly seven million light years across.
That puts KKs 3 well outside our group. There are other nearby groups, but KKs 3 isn’t a part of them either. It appears to be truly isolated.
It’s small, too: It has a total mass of about 20 million times that of the Sun. The Milky Way’s mass is 10,000 times larger! That makes KKs 3 incredibly faint. It’s amazing it was found at all. It was discovered in 2000, but not conclusively shown to be isolated until this new study using the Hubble Space Telescope. The image at the top of this post shows the galaxy. You can see it as a faint, spread-out smear in this negative image. By coincidence it happens to lie in the sky right next to a globular cluster, a smaller ball of stars presumably orbiting the Milky Way. Not only that but a pair of red stars in our galaxy happens to lie right in the middle of KKs 3.
This shows how hard it is to find these suckers. They don’t exactly stand out. Even faint nearby stars can confuse the surveys.
KKs 3 is also old. The majority of stars in it formed about 12-14 billion years ago in one big episode of star birth; that wasn’t long after the Universe itself formed. It had a couple of other, smaller bursts of star formation long ago, but ran out of gas (literally) after the last one, and no new stars have been created.
But this is all great news for astronomers: KKs 3 is a relic, so isolated and old it probably hasn’t changed much in a long, long time. Studying it is like having a time machine to study the ancient Universe. And we think that, billions of years ago, collisions between small galaxies like KKs 3 are what built up much larger galaxies. We know that the Milky Way is currently eating a few other small galaxies, so we can study those events and compare them to what we see in KKs 3 to learn more about how this process may have occurred so far in the past.
I know that photo of KKs 3 doesn’t look like much; splashier galaxies are so much easier and fun to look at. But this doesn’t make it any less important. You can search where the light is bright all you want, but if what you’re looking for isn’t there, well, what are you going to find?
from Bad Astronomy http://www.slate.com/blogs/bad_astronomy/2014/12/27/kks_3_a_nearby_faint_small_galaxy.html
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2014年12月26日 星期五
Cetus Duo M77 and NGC 1055
Get an Up-Close Look at the Lunar Surface with These 3D Apollo Images
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2014年12月25日 星期四
This Comet Lovejoy
Merry Nerdmas!
Happy holidays, nerds!
And yes, that's our actual tree topper. Proof:
May all your days be filled with geekery.
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2014年12月24日 星期三
IC 1795: The Fishhead Nebula
A Visit to India: New Space Collaborations and New Friendships with Role Models for Women in STEM
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2014年12月23日 星期二
The Cliffs of Comet Churyumov Gerasimenko
Angara Launch Successful
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Planetary Surface Processes Field Trip: Day 4
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Planetary Surface Processes Field Trip: Day 1
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Summary of Stealth NASA ISS Workshop
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Sam Keller
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Larry Vogel
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Russia Launches Angara 5
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Pretty pictures of the Cosmos: Infinity
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One Press Release With a Year's Worth of Highlights
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More Unfunded Commercial Partnerships Announced by NASA
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NASA Selects Commercial Space Partners for Collaborative Partnerships
December 23, 2014
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Frosty Slopes on Mars
2014年12月22日 星期一
The Mysterious Methane of Mars
NASA Takes Giant Leaps on the Journey to Mars, Eyes Our Home Planet and the Distant Universe, Tests Technologies and Improves the Skies Above in 2014
December 22, 2014
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Twinkle Twinkle Little Star, An Astrophysically Correct Book and Song Are Now What You Are
This is so fun: my friends Zach Weinersmith of SMBC and Henry Reich from Minute Physics have written an astronomically corrected version of the song “Twinkle Twinkle Little Star” for kids!
They also put together a totally adorable short video with Henry singing the song:
They have all kinds of e-versions available, and you can pre-order a physical copy, too. The drawings are by children’s book illustrator Chris Jones, so this really is top-notch stuff.
When I first saw it I thought I saw a mistake in it, but I was wrong. I point it out so others don’t misunderstand it the way I did. The lyric is about a pulsar: “Out away from Earth your drift, this is known from your redshift.” I mistook this line to say we know its distance from its redshift, but that only works for very distant galaxies, not pulsars, which are inside our own galaxy. But I misunderstood; they’re saying we know it’s moving away from Earth by its redshift, and that’s technically correct. So there.
Anyway, this has come out just in time for the holidays. Go buy it, and turn more kids into little science pedants!
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NASA Commercial Crew Partners Complete 23 Milestones in 2014, Look Ahead to 2015
December 22, 2014
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Orion Astronaut View on Re-Entry
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So a Galaxy Walks Into a Bar...
Adam Block is one of my favorite astrophotographers. Now, he has a bit of an unfair advantage: The 0.81-meter Schulman Telescope at the top of a mountain in Arizona at his disposal. He’s also really good at finding interesting but lesser-known objects, and has a serious knack at creating incredible images of them.
I’ve featured his images many many times on this blog, but I think this may be the very best I’ve ever seen: the spiral galaxy NGC 1398.
Holy resonance-amplified stellar awesomeness!
NGC 1398 is a galaxy roughly the same size as out Milky Way, located about 65 million light years away in the Fornax cluster, a cosmic city of hundreds of galaxies. It’s what’s called a barred spiral, due to the long rectangular feature right in the middle. It also has that peculiar ring around the bar, a second double-armed ring farther out, and then a couple of dozen fluffy-looking spurs.
Bars are pretty common in big disk galaxies; the Milky Way has one. They form due to the way gravity works in the disk. In our solar system, essentially all the mass is in the Sun, and the planets orbit it in nice, regular paths. But in a disk galaxy the mass is spread throughout the disk, and that changes things. If you disturb the disk (say a nearby galaxy passes, and its gravity distorts the disk a bit) that perturbation can grow, propagating through the stars and gas.
The math is a tad complex, but the end result is the bar pattern, like a traffic jam in the central galaxy. That bar itself has a peculiar gravitational field, and can affect stars and gas outside it.
The bar rotates around the center of the galaxy with some period. At a certain distance from it, stars and gas orbits at some small multiple of that period, like twice as long, or four times as long. This simple relationship, called a resonance, pumps up the stars and gas, a bit like the way pumping your legs on a playground swing at the right frequency can make you go higher.
That’s what creates the inner ring. It’s actually a pair of tightly wound spiral arms that overlap (you can see that a lot more clearly in a WISE image of the galaxy in the far infrared). The outer ring is also really just tightly constrained arms, too. Outside of that, the spurs are patchy—what’s called flocculent, which is just a cool word (it means patchy, like clumps of wool or cotton).
In Adam’s picture (a total of an astonishing 20 hours of exposure) you can also see a lot of smaller galaxies, almost certainly in the far distant background. I do mean “distant”: they’re a billion light years away or more. The bright red star in the lower right, on the other hand, is in our galaxy, probably only a few hundred or thousand light years away.
Quite the range in this one photo! And a spectacular example of what happens when you take a handful of simple ingredients—stars, gas, gravity, and a few laws of physics—and let them interact for a few billion years.
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2014年12月21日 星期日
Tyrrhenian Sea and Solstice Sky
2014年12月20日 星期六
Apollo 11 Landing Site Panorama
Detecting an Exoplanet… Without a Telescope
Years ago, when the first transiting exoplanet (HD 209458b) was found, I was startled to realize that it could be easily detected using a small, inexpensive telescope.
Transiting exoplanets are planets that orbit other stars, and from Earth we just so happen to see their orbit edge-on. That means it passes in front of their parent star (that’s the transit bit), blocking a fraction of its light. A tiny fraction, usually far less than 1%. But if the star is bright this dip in brightness can be spotted in small telescopes. I remember doing the calculations and finding that a 30 cm telescope could detect HD 209458b in a single night’s observations. Tough, but possible.
That meant an amateur astronomer could detect exoplanets! What didn’t occur to me at the time is that you don’t necessarily need a telescope to do so.
David Schneider, an editor at IEEE Spectrum, has described a setup using a digital camera and 300mm telephoto lens that has allowed him to detect the transit of the exoplanet HD 189733b, a so-called hot Jupiter, a massive planet orbiting very close to its star. The transit depth is about 2.6%, and his data look pretty good to me. He based his work on an amateur astronomer (vmsguy on the Cloudy Nights forum) who has also posted data that look pretty convincing.
Basically, the idea is to take several exposures over the course of the transit, taking care to make sure you get pictures taken before and after the transit. That’s your baseline. Using software to align the images and examine the stars (both vmsguy and Schneider used IRIS, which is Windows only, but other packages exist), you measure the brightness of the star over time to see the transit.
Not that it’s that easy! In reality you do relative photometry: You measure the brightness of many stars at the same time, so that a passing cloud doesn’t dim your star and make you think you’ve found an exoplanet. You also have to take other calibrations (like darks and flats), and apply them carefully. But it’s not impossible, and in fact sounds like fun.
Mind you, Schneider went all-in, even to the point of building his own gear to track the stars; but if you have a telescope you can always just use the motor drive that does that for you. The point is, you can detect exoplanets using just a camera, a good long lens, and a solid mount!
That’s amazing. I’ve been thinking of trying this sometime using my own 20 cm ‘scope; a lot of exoplanets are within range. But I’m still figuring out how to take astrophotographs, and believe me, I know how addicting this can be. I used to do this for a living, and if I get the software and start observing, I’ll be down the rabbit hole pretty quickly!
But in some ways, that’s the point. If you have the time and resources, it’s pretty amazing what you can do. You can even observe alien worlds.
Tip o’ the lens cap to James Walker .
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2014年12月19日 星期五
Reflections on the 1970s
Video: Ride along with Orion as It Plummets Back to Earth
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Random Space Fact Videos
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A new Chang'e 3 and Yutu image archive
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Video Gives Astronaut’s-Eye View Inside NASA’s Orion Spacecraft
December 19, 2014
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Here's How Planetary Science Will Spend Its $1.44 Billion in 2015
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SpaceX Completes First Milestone for Commercial Crew Transportation System
December 19, 2014
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Hubble Sweeps a Messy Star Factory
2014年12月18日 星期四
NGC 7331 and Beyond
NASA, Planetary Scientists Find Meteoritic Evidence of Mars Water Reservoir
December 18, 2014
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NASA’s Orion Arrives Back at Kennedy, Media Invited to View Spacecraft
December 18, 2014
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75th Anniversary of NASA Ames
NASA, SpaceX Update Launch of Fifth SpaceX Resupply Mission to Space Station
December 18, 2014
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NASA’s Kepler Reborn, Makes First Exoplanet Find of New Mission
December 18, 2014
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Peninsular
I love photos of the Earth taken from space; our deserts, oceans, islands, volcanoes, farmland, forests… all of it.
But there’s something special about seeing something recognizable, even iconic, from space. Perhaps we’re used to seeing such things on maps, but a photo of it adds the dimension of reality.
I’m not sure. But no matter why, it’s hard to deny this is just straight-up cool:
I’ve spent a lot of time on this peninsula; family vacations when I was younger, visiting friends when I was older, watching the odd rocket launch or three. My folks lived there for many years, so seeing this from space reminds me of combing beaches for shark teeth when my daughter was little, getting sunburned like an idiot despite slathering on lotion, sweating maniacally in March.
At night, from space, the outline of Florida makes it so obvious (like Italy; perhaps peninsulae are easier to recognize). The lights of the city are both lovely to see and appalling to seriously consider; the light pollution is overwhelming, ironically drowning out everything in the night sky except for the few brightest objects… like the International Space Station passing overhead, from where this photo was taken.
Our technology has made it possible to go up and look down, but much harder to stay down and look up. If there is some sort of allegorical conclusion to be drawn here, well, I’ll leave it for you to consider.
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Scientists Discover 38% of the Earth
OK, so the title is a little tongue-in-cheek, but it's sorta true: Mineralogists have finally found naturally-occurring samples of what may be the most common mineral on Earth: what’s called silicate perovskite, or (Mg,Fe)SiO3.
They’ve also officially given it a name now too: Bridgmanite. Percy Williams Bridgman won the Nobel in 1964 for studying high-pressure minerals… and that’s a clue to why this mineral was so hard to identify.
Bridgmanite can only exist under conditions of high temperatures (at least 2100°C) and pressure (240,000 times the sea level atmospheric pressure—a crushing 240 metric tons per square centimeter!). It’s thought to be abundant in the Earth’s lower mantle—a region 660 to 2900 km beneath Earth’s surface. The molten rock in the mantle is fluid, moving incredibly slowly inside our planet. Any bridgmanite in the mantle brought up toward the surface slowly breaks down under the cooler and lower pressure conditions, which is why it’s remained elusive, even though the mineral may make up as much as 90 percent of that part of the mantle (and therefore more than a third of the entire planet).
The scientific break came in the form of a meteorite, called Tenham. Long ago, two asteroids collided, and the impact created high temperatures and pressures. Bridgmanite formed, and the piece cooled too rapidly for the mineral to decompose. In 1879 the rock fell to Earth in Australia, where it was found and eventually determined to have different kinds of high-pressure minerals in it. Bridgmanite exists in it in very small grains, typically only about 1 micron wide (a human hair is typically 100 microns in width), but it’s there. It was announced earlier this year, but the scientists just published their paper about it in November.
This is quite a boon! It’s difficult to reproduce the conditions in the deep Earth, and even if you can it’s even harder to study what you get. In this case, it’s like we got a sample of the Earth’s lower mantle for free. It’s also a nifty crossover between different disciplines: Meteoritics, high-pressure physics, mineralogy, just to name some.
And also, it’s just amazing. We live on a ball of rock and metal 12,740 km across, with a staggering 1 trillion cubic kilometers of material in it, the vast vast majority of which we can never directly see. I wasn’t even aware that we didn’t actually know for sure what made up over a third of our own planet.
Science! Astronomy may be my passion and my love, but sometimes it’s good to remember that science also tells you, literally, what’s going on right underneath your feet.
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2014年12月17日 星期三
Geminid Fireball over Mount Balang
Infinite Visions, One Planetary Society
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NASA Delays Asteroid Redirect Mission Concept Selection until 2015
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SpaceX to Attempt First-Ever Ocean Barge Rocket Landing
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NASA Media Brief On Asteroid Mission No One Supports
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Dark Sky in Canarias
Because why not, here’s a luscious time-lapse animation of the sky over La Palma, Tenerife, and El Hierro, three of the Canary Islands off the coast of Morocco:
This video was taken by photographer Imanol Mujika. He has a stunning Flickr gallery, too.
I’ve been to La Palma, and the clouds really do roll in like that. I like how you can see them swell and disappear over the city (I think it’s Santa Cruz in the video) like waves on a beach.
Also, toward the end (at the 1:55 mark), there’s a star trails shot where the long exposure shows the stars as streaks due to Earth’s rotation. Stars on the celestial equator—the part of the sky directly above the Earth’s equator—make straight lines, but toward the right (north) and left (south) they curve more, as they circle the pole. But they curve in opposite directions!
That’s just the natural consequence of the wide-angle shot, being able to see the motions of stars across a big chunk of sky. Near the celestial poles, the stars make smaller circles, so we see the curvature of their trails changing with position. I have a more detailed explanation in an earlier post, if you’re curious (and you should be!).
Seeing this makes me want to get under the stars again... and now that it's winter, Orion, Taurus and all the wonderful chilly weather stars are back at a decent time of night. Time to warm up my camera...
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City Lights Shine Brighter During the Holidays
OIG: NASA Reliance on DCAA Increases Costs
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NASA to Discuss Today Asteroid Redirect Mission Capture Concept, Next Step in Journey to Mars
December 17, 2014
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2014年12月16日 星期二
SpaceX Will Attempt Rocket Ship Landing on a Drone Barge
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W5: Pillars of Star Formation
No One Reads The Federal Register Any More
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RD-180 Bad; RD-181 Good
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Like A Bad Penny: Methane on Mars
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Is Dava Newman's Nomination In Limbo?
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NASA Awards Launch Services Contract for Transiting Exoplanet Survey Satellite
December 16, 2014
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Active, Ancient Organic Chemistry on Mars
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NASA Rover Finds Active, Ancient Organic Chemistry on Mars
December 16, 2014
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Deadline Change, Rule Change and Prize Money Awarded in Google Lunar X Prize
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NASA Analysis: 11 Trillion Gallons to Replenish California Drought Losses
December 16, 2014
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Sunset Over the Gulf of Mexico
GAO: Webb Continues To Experience Significant Delays
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OIG: NASA Does Not Do A Good Job With Space Act Agreements
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50 Shades of 67/P
That picture shown above is, seriously, a full-color photo of the comet 67P/Churyumov-Gerasimenko.
It was taken by the Rosetta spacecraft on Aug. 6, 2014, when the probe was still 120 km (75 miles) from the comet (long before the Philae lander was deployed). The OSIRIS camera on board has red, green, and blue filters that allow the camera to mimic what the human eye sees. It’s not exact, but it’s close.
And what you see is… grey. Which means the comet really is just kinda overall grey.
That doesn’t surprise me. Comets aren’t really loaded with the sorts of colorful minerals that make Mars or Europa or even our own Earth so gloriously hued. They’re mostly water ice and rock, with other things thrown in for good measure.
But you might expect some variation when you look at the comet in detail. But it’s very smoothly grey; there’s very little change in the color composition across the comet. That means there’s probably physical homogeneity across its surface. If there are any interesting minerals or materials in the comet, they appear to be distributed pretty well.
That does surprise me; I was expecting to see patches of ice at least on the surface, and those reflect blue light better than red. But we see no blue patches at all. The water ice in the comet is mixed in with the other stuff.
That’s not the case with other comets; for example, Hartley 2 is also double-lobed, with a waist in between them, similar in shape to 67P. But observations using the EPOXI spacecraft show the waist is emitting water ice, while the lobes blow out more carbon dioxide. The waist is also smooth in appearance, while the lobes are rougher. It’s unclear why this might be.
But 67/P, for all its similarity in overall shape, is clearly a different beast than Hartley 2. That’s telling us something. Perhaps they were born in different parts of the solar system, and so are constructed differently (we know that to be the case for some by looking at isotope ratios in different comets). Maybe something happened as they aged—4.55 billion years is a long time, after all—that changed them. It could be that 67/P's outgassing and dust have coated its surface everywhere. Or maybe comets are just a diverse group, every one different from another. None of these circumstances would be surprising.
There’s another possibility, too: Simulations of the early solar system show that our Sun may have stolen the vast majority of its comets from other stars! If that’s the case, then that would go a long way toward explaining why comets are so different from each other. They were born in different solar systems!
It’s hard to express just how awe-inspiring that is. We’ve always assumed comets were like time capsules from the ancient solar system (if weathered and worn over the eons). But they actually may be samples of alien stars, transplants from elsewhere in the galaxy.
Thinking about this literally raises the hairs on the back of my neck.
So gaze upon that photo of 67/P once again, and think about what you may be seeing. I know I’ll never use the word “grey” to mean boring ever again.
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2014年12月15日 星期一
The Potsdam Gravity Potato
This is How Broken NASA Is
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Virgin Galactic Brings DalBello Aboard to Focus on LauncherOne
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Reporting from the 2014 Fall Meeting of the American Geophysical Union
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A Rain of (Teeny) Asteroids
Over the weekend, the Geminid meteor shower came to a peak. This annual event occurs when the Earth plows through debris left behind by the asteroid 3200 Phaethon as it orbits the Sun (it gets so close to the Sun that bits of the rock vaporize and blow off the asteroid). Each little bit of interplanetary detritus is moving at about 35 km/sec (22 miles/sec), fast enough that as it rams through our air, it heats up enough to become incandescent, and we see a “shooting star”.
I was out Saturday night (Dec. 13), and over the course of two hours I saw so many I lost count; I’m pretty sure I spotted at least 80. I wasn’t able to get any Geminids on camera (grrrrr), but happily photographer Neil Zeller had far better results:
Spectacular! He drove up northeast of Calgary to get nice dark skies, and it was clearly worth the trip. The photo is actually a composite of several exposures; he was facing northwest and captured the Milky Way, several Geminids, and a lovely green aurora on the horizon (Zeller has an astonishing gallery of aurora photos on his website). On the far right you can just see an interesting pair of stars tightly spaced; that’s Mizar and Alcor, the stars in the bend in the Big Dipper’s handle.
As you can see, all the meteors seem to point in the same direction. That’s because they do! The meteors appear to come from a part of the sky near the head of Gemini (hence their name), and radiate away from that point in all directions. It’s a perspective effect, like driving through a tunnel and seeing the lights on the walls appear to come from the same spot ahead of you, and streak away to the sides.
As I stood under the chilly Colorado sky Saturday, this radiating effect was pretty strong; I saw meteors in any part of the sky I looked, and they always pointed back toward Gemini (except for one which was a random meteor unrelated to the shower; on any night you can usually see a few per hour). I saw every flavor of meteor, too: long streaks, short ones, faint ones, bright ones, and one that flared about as bright as Jupiter (magnitude -1 or 2 if you want details) that left a luminous vapor trail that lasted for just a second or two. That was amazing.
This was easily the best meteor shower I’ve ever watched myself. It’s usually too cold and cloudy this time of year to see it, but things worked out well; in fact, as I write this (the day after the shower) it’s snowing!
And I did get a lot of very pretty pictures from the night, including this one of Orion through the trees (and Sirius, the brightest star of the night sky, to the lower left). It was totally worth the cold fingers, toes, and nose.
Tip o' the lens cap to Daggerville on Twitter.
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NASA Tests Software That May Help Increase Flight Efficiency, Decrease Aircraft Noise
December 15, 2014
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2014年12月14日 星期日
Molecular Cloud Barnard 68
2014年12月13日 星期六
NASA's 2015 Budget Increase is All But Confirmed
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The Infrared Visible Andromeda
SpaceX Spreads Out
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2014年12月12日 星期五
Crystals on Mars
NASA Highlights Drought, Mars, Arctic Warming at American Geophysical Union
December 12, 2014
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The Planetary Society’s Global Volunteer Network
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Pretty pictures of the Cosmos: Strange and spooky
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LightSail Completes Testing, Announcement Expected in January
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New Churyumov-Gerasimenko Shapemodel!
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Super Guppy Spends a Restful Night in the NASA Langley Hangar
2014年12月11日 星期四
NASA's Budget Increase Is A Step Closer to Reality
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Moondog Night
Correcting NASA's Inaccurate Infographic
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Brief Venus Express update: Not quite dead yet
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The YORP Effect and Bennu
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Spaceport America Needs More Spaceships
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NASA, SpaceX Update Launch of Resupply Mission to the Space Station
December 11, 2014
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