The entire universe in blog form

Dec. 18 2014 7:15 AM

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.

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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).

Earth
Layers in the Earth. 1) Inner core, 2) outer core, 3) lower mantle (the layer in question), 4) upper mantle, 5) lithosphere, 6) crust.

Drawing byMats Halldin

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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Dec. 17 2014 11:15 AM

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.

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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 ...

Dec. 17 2014 7:15 AM

Hour by Hour, the Phases of the Moon for the Entire Year of 2015

Just the other day I wrote about the good folks who create video at NASA’s Goddard Space Flight Center. And now I get to do it again: They just released their Dial-a-Moon page for 2015, which lets you display the hour-by-hour appearance of the moon for the entire year.

They also put out a video compiling all the images for the year into a single animation. You might expect it to look like the Moon is just sitting there, with the phase changing as the terminator (the day/night line) sweeps across its face. But that’s not what you get at all. Watch:

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Trippy!

The Moon orbits the Earth in the same amount of time it takes to spin once. This means it always shows us the same face … except not really. The Moon’s rotation is constant, but the velocity it travels in its orbit around the Earth changes because that path is an ellipse. When it’s closer to Earth it moves faster, and slower when it’s farther away. This mismatch lets us peek a bit “around the side” of the Moon. The Moon’s spin axis is also tipped a bit with respect to its orbit, and that allows us to see over the northern and southern poles, too.

When added together, you get that mesmerizing nodding and weaving motion, which is called libration.

The video has some nifty extras too. At the top left it shows the Moon’s position in its orbit around the Earth, as well as the phases of both the Earth and Moon.

Behind the big Moon in the center is a line representing the Moon’s orbit seen edge-on. On the left is the Earth, and on the right it shows how far away the Moon is, in units of the Earth’s diameter (12,740 kilometers or 7,900 miles).

On the bottom left is a diagram of the Moon, with a blue and yellow dot; the blue is the sub-Earth point and the yellow is the sub-solar point.  In other words, if you were standing on the Moon at the position of the blue dot the Earth would be exactly overhead, and if you were at the yellow dot the Sun would be directly overhead. Note that when the Moon is full to us on Earth, the yellow dot is smack dab in the center near the blue dot: The Sun is shining straight down on the half of the Moon we see. When the Moon is new (completely dark), the yellow dot is on the far side of the Moon; the Sun lights up the half we can’t see, and the half facing us is dark.

Finally, on the lower right are lots of fun numbers: date/time, the phase (percentage of the Moon illuminated as seen from Earth), how big it appears, how far it is, and so on.

If you’re planning any detailed lunar observations, the GSFC page is pretty useful. I know I’ll use it to plan our future Science Getaways trips; we try to schedule them around new Moon so we can see the stars when I take my telescope out.

And even if you don’t need that kind of detail, this is just a way cool thing to have around. There’s also a video that shows just the Moon without any of the annotation, and a view as seen from the Earth’s Southern Hemisphere as well, with the Moon upside-down. Wacky Southern Hemisphereans.

And don’t forget this is a simulation, based on images taken by the Lunar Reconnaissance Orbiter. The real thing is even better, so go outside and look! You may get inspired. A couple of friends of mine were.

Dec. 16 2014 12:24 PM

Meteor Not?

So in my post about the Geminid meteor shower yesterday, I said that I didn't catch a single Geminid in my photos, and that's true. But going over them carefully, I happened to see something a bit weird, and I'm not sure what to make of it.

I took many shots of Orion, since it was perfectly placed over a tree, and any meteors going across it would make for a great photograph. I kept the exposures to 20-30 seconds, since the sky background was pretty bright, and I didn't want the stars to trail too much. While I didn't get any Geminids, I did happen to see this tiny streak:

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You can see the three stars in Orion's belt at the top, and the fuzzy glow of the Orion Nebula, the nursery to a lot of young bright stars. And there, just below the third star in Orion's "dagger," there's that little blip. Is that a meteor?

I'm not sure. It's not a Geminid for sure; given Orion's position in the sky, a Geminid would leave a left-to-right streak in this photo. It's not in the previous or following photo, taken seconds earlier and later. 

I'm not sure what to make of it. Most meteors would leave much longer streaks, but if the bit of cosmic debris happened to be heading almost straight toward me, it would leave a short streak due to perspective. If it's not a meteor, what could it be? Sometimes subatomic particles can leave similar streaks in a digital detector (these are typically called cosmic rays), but I've never seen one in my usual use of a regular camera. It may have been a bird lit by city lights, but the streak doesn't wiggle, and is so short that seems pretty unlikely. Same for an insect much closer to the camera. 

It seems weird to think that a small bit of interplanetary debris sloughed off by some ancient collision between two asteroids millions of years ago and hundreds of millions of kilometers away may be the least unlikely explanation, but there you go. 

Astronomy does sometimes provide an unusual perspective.

Dec. 16 2014 7:30 AM

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 kilometers (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.

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And what you see is … gray. Which means the comet really is just kinda overall gray.

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 gray; 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 “gray” to mean boring ever again.

Dec. 15 2014 1:52 PM

Comical Immunity

Speaking of vaccines, my pal Maki Naro is a fantastic illustrator and pro-science guy, and he just put up a wonderful comic about why vaccines are important.

I love this. He hits on lots of critical topics, like how our immune system works, how vaccines prime that system to fight off diseases, why herd immunity is important, and why it's hard to keep up with evolving viruses.

makinaro_antivaxcomic2

Drawing by Maki Naro

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Just as importantly, he hammers the anti-vaxxers who so richly deserve it, like Jenny McCarthy, Andrew Wakefield, and RFK Jr. Maki shows why their claims are not just wrong but in most cases hugely, egregiously wrong. And it's all done in a lovely, palatable comic form, making it easy and fun to read. 

Maki draws more comics like this for Popular Science, too. I like his style, and I hope you do too.

Dec. 15 2014 11:27 AM

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 kilometers/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:

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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 that 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!

Orion
The mighty hunter. Click to embiggen.

Photo by Phil Plait

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.

Dec. 15 2014 9:39 AM

Opting Your Kid Out of Vaccination? That’s Sickening.

Hmmm, it’s been a while since I’ve posted on how anti-vaccination propaganda is making people sick and putting children needlessly at risk for terrible diseases.

[Opens up map, looks around, sees blinking red alarm light over Michigan.]

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Ah, Michigan, that bifurcated mitten by the lake. I spent three years at U of M and grew quite fond of it.

But then, I didn’t get measles or whooping cough while I was there.

You have a decent risk of that now, due to low vaccination rates. In Traverse City, a recent outbreak of pertussis forced the closure of a charter school with 1,200 students (there were 10 confirmed cases and 167 probable cases) and infected children at 14 other schools.

Why did this disease hit schools so hard? The reason is almost certainly exactly what you’d think: Vaccination rates for children in schools are low because parents have been opting them out.

Most states have mandatory vaccinations for children to attend public schools, but they also have opt-out waivers for parents who don’t want their children vaccinated for religious reasons … and for “personal reasons.”

This means anti-vaccination reasons. And you know how I feel about that. Virtually every claim made by anti-vaxxers is wrong, or a gross distortion of the truth.  The actual truth about vaccines is that they are extremely effective and their risks are minimal.

I’m not a fan of religious waivers—especially when it comes to health care workers, for example—though I understand that’s a political hot potato (even though, in reality, very few religions forbid vaccinations).

But personal waivers? The more I think about it, the more I come down pretty clearly on it: If your child is able to get vaccinated, and you choose not to do so, then your child should not be allowed to attend public school.

It’s that simple. I’ve made this argument before:

In some areas, public school authorities have mandated that students be vaccinated for various diseases, and that of course can run afoul of parents’ beliefs. I’ve wrestled with this problem for a while, and I eventually came to the conclusion that a parent does not have the right to have their child in a public school if that child is unvaccinated, and for the same reason health care workers should not be unvaccinated. It all comes down to a very simple reality: It puts other children at risk.
If you want to rely on the public trust then you have an obligation to the public trust as well, and part of that obligation is not sending your child to a place with other children if they aren’t immunized against preventable, communicable diseases.

When you send your kid to a public school, this is no longer a personal decision. It’s a very public one, and you are putting thousands of people at risk for diseases that can cause grave harm, and even be fatal. And yes, I’m vaccinated, and so are my wife and daughter, but not everyone can get vaccines due to health reasons (people who are immunocompromised, for example). Some babies are simply too young to get vaccines yet, for example, and they are at very high risk for infectious diseases like pertussis and measles.

And that, I am very sad to say, matters very much.

Update (Dec. 15, 2014 at 16:15 UTC): I have just been informed that a new policy in Michigan will start in the new year; parents will have to have their opt-out forms certified by the local health department before choosing not to vaccinate their child (the idea being they will then get more and better information about vaccines). That's a step in the right direction, but in my opinion still doesn't go far enough; if that child attends a public school the result can be serious outbreaks, as we've seen. Thanks to Jamie Mueller on Twitter for the tip.

I have said this before, and as long as we have outbreaks of diseases due to low vaccinations rates I will continue to say it: Don’t listen to the anti-vax rhetoric. They’re wrong. Instead, talk to a board-certified (i.e. non-quack) doctor and find out if you need to get your vaccinations (including boosters) and if you should vaccinate your family.

People shouldn’t be dying because of diseases we can easily prevent. But they are. Do your part.

Thanks to Luke Schmerberg for sending me the news about Michigan.

Update (Dec. 15, 2014 at 16:00 UTC): I changed the phrasing of the sentence about unvaccinated students not being allowed to attend public schools for clarity.

Dec. 14 2014 7:30 AM

Fix’d in Heaven’s Air

We live on a whirling ball of rock thousands of kilometers across. As it happens, most balls of rock that size in the Universe are whirling, so it’s not really weird. It just seems weird.

The reason it seems weird is that the rotation of the Earth is pretty slow when it comes to things we can perceive; it’s not like being on an amusement ride with a small radius and rapid spin. We’re pinned to the surface of a planet, and it’s huge.

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We’ve evolved over a zillion years to think the Earth is fixed, and the sky spins around us. That’s why we say the Sun rises, and not “the Earth’s west-to-east angular motion has caused a reflexive apparent motion in the otherwise nearly fixed Sun such that it seems to move in a westward fashion above the eastern horizon,” which honestly, would be too pedantic even for an Internet commenter.

But it’s true. The stars move across the sky because we move under them, we just don’t see it that way.

But what if we could? I bet it would look like this video by neurologist and photographer Alex Rivest:

Wheee! That’s fun. He took some time-lapse animations of the sky, then set them up so the stars stay fixed, letting the ground move (he was inspired to try this by a video created by José Selgado). It’s an odd, and subtly disturbing effect. It was neat to see his Mount Everest footage in there, too.

I also stumbled on an interesting illusion: If I kept my eyes on a feature in the sky (a star, or a dark patch in the Milky Way) it does look like the ground is rotating, but if I looked near the edge of the frame, or right where the ground and sky meet, it looks like the stars are moving, or a weird combination of both sky and ground moving.

Our brains are ridiculously easy to fool. But you knew that, right?

Dec. 13 2014 7:45 AM

An Island Makes Waves in the Sky

I don’t know why cool cloud patterns seen from space fascinate me so; maybe it’s just my inherent love of science, clouds, space, nature, and art.

Actually, after writing that sentence, maybe I do know why.

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Also, sharing that love is fun, too. So for you, here is a really nice shot of a wave cloud pattern seen by Landsat8:

ship wave clouds
The Earth provides us with another gorgeous example of fluid dynamics.

Photo by Jesse Allen using Landsat data from the U.S. Geological Survey

What you’re seeing are called “ship wave clouds,” because the overall pattern resembles the waves of water as a ship moves through the ocean. The cause of this is Île Amsterdam, an incredibly remote and tiny volcanic island located in the southern Indian Ocean. It’s only about 10 kilometers across, and the peak reaches to about 850 meters above sea level. You can just see the edge of the island on the left-hand side of the image, peeking through the hole in the clouds.

As a steady wind blows over the volcano, it rises up and cools. Moisture in the air condenses, forming clouds. But as the air cools it sinks, warms up, and the water evaporates again, so the clouds disappear. The warm air rises, and boom! Repeating pattern. At the same time, the wind gets pushed around the volcano as well, so the pattern gets wider downstream.

This photo is one of the best I’ve ever seen of the phenomenon … though when it happens over an island chain it’s pretty amazing as well. I see similar things sometimes as the wind blows over the Rocky Mountains, just a few kilometers to the west of my home. When wind, water, and geology interact, it’s a canvas on which nature paints nearly infinite varieties of beauty.

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