The entire universe in blog form

Sept. 18 2014 7:30 AM

Red and Green Ghosts Haunt the Stormy Night

Randy Halverson is a photographer and has quite a gift for time-lapse video (I’ve featured his work many times on the BA blog).

He recently sent me a video he took in central South Dakota that is quite astonishing. While photographing a storm at night, he caught two very rare events at the same time: sprites, and gravity waves rippling through airglow!


First, here’s the video, because it’s amazing.

Did you see the sprite? It happens just before the six-second mark in the video. Look to the right, just above the storm cloud. The red flash is obvious once you spot it.

Sprites are a phenomenon associated with lightning storms; they’re electrical discharges from the top of the storm cloud, not the bottom. They’re not really understood, but they occur simultaneously with lightning between clouds or from cloud to ground, and glow eerily red. They were only first discovered in 1989 (officially, that is; pilots have been reporting them for decades, but no one outside that cadre really took them seriously) so not a huge amount is known about how they operate.

red sprite
Close-up on the red sprite. Click to enfairyenate.

Photo by Randy Halverson, used by permission

On a larger scale, you can also see green ripples moving across the sky. The green is airglow, molecules in the upper atmosphere that are energized by the Sun during the day, and give off that energy as light at night. This occurs via chemoluminescence; a process where the excited nitrogen and oxygen atoms molecules bump each into other and form bonds, giving off that light.

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 only recently learned about this phenomenon, when I saw a time-lapse video taken in Chile, a world away from South Dakota.

Several years ago, Randy sent me an email asking about a weird rippling glow he saw in some footage he had taken. I wasn’t sure at that time what it was (though I was sure it wasn’t an aurora), and we agreed it could be airglow. It’s funny that he would send me this new video right after I finally learned what that rippling was! If Randy had asked me two weeks ago I wouldn’t have known. He found out on his own, and now we both understand. And I hope now you do too.

The sky above us is just incredible. There’s still so much to discover, so much to figure out, so much to explore. And it’s all right there, just over our heads.

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Sept. 17 2014 11:18 AM

A Bridge Across the Sky

A couple of months ago I spent a few days in western Colorado, far away from city lights. I was with a group of science enthusiasts for Science Getaways, taking a week long vacation chock full o’ science.

That part of the country is blessed with dark skies and fantastic weather, and I took my telescope out every night to view the heavens. But just standing there and looking up was surpassingly moving. The Milky Way loomed large over the land, stretching across the sky, so bright it was a palpable thing.

A half a world away, that feeling was captured perfectly by astrophotographer Amirreza Kamkar, who took this incredible picture in Abyaneh, Iran:

Sept. 17 2014 7:30 AM

Ring Around the Rainbow

The basic physics of a rainbow is pretty simple, really. Sunlight enters the front of a raindrop. It hits the back side of the drop, reflects, and then heads back out the front side again. The light bends a little bit when it enters and exits the drop—scientists get all fancy and call this refraction—and different colors bend by different amounts. The light bends change direction by a total of about 138°, but red light bends a little less, blue light a little more.


So, to see a rainbow, you face away from the Sun (180°), then look about 42° away from that point (180°–138°). The drops in an arc along that angle will then bend the light back toward you, and you get a rainbow, with the colors spread out a bit because they bend by different amounts.

Oh, wait. Did I say “arc”? Because technically, any raindrop 42° away from the anti-solar point (ooh, fancy science-speak again) will bend the light back to you. We see rainbows in the sky because in general the ground is close to you. When we look up toward the sky we see for a long way, and there are lots of raindrops along your eyeline that can add their light together to make the rainbow. When you look down, the ground gets in the way, there aren’t as many drops, and you don’t see a rainbow.

In general. Not always. For example, you could be in an airplane when it’s raining. If the Sun is in the right spot, and you look out the opposite side, you could in fact see a rainbow making a full circle …  just like this:

Incredible full circle rainbow (and secondary, too) seen from an airplane.

Source: oskarslidums on reddit

Oh, wow! I knew scientifically this was possible, and I’ve heard pilots say they’ve seen them, but I’ve never actually seen a picture of one. That’s amazing.

Again, every raindrop in the air that’s 42° away from the spot in the sky opposite the Sun can bend the light back toward you. All those drops are the same distance from that point, and that defines the edge of a circle.

Even better, there’s a secondary bow, due to light reflecting twice inside each raindrop. That reverses the colors, so the secondary bow goes red to blue inside to outside. You can also see Alexander’s dark band in between them; drops located in that region bend light away from you, so it looks darker. Inside the primary bow it looks brighter because drops there bend light at you. The colors bent by drops there all overlap with each other, adding back together to create white light, so inside the primary bow there’s no color. I describe how all this works (with links) in a previous post. A little searching turned up another shot of a circular rainbow from the air, though it's not quite all in the single picture. It shows good supernumerary arcs, though.

If you look carefully, the shadows on the ground inside the rainbow all seem to point to its center. That’s just geometric perspective; since the center of the rainbow has to be 180° around the sky from the Sun, shadows have to point in that direction!

By the way, you can get higher order rainbows; I learned just recently that the tertiary bow is in the direction toward the Sun, the fourth just outside it (and is very faint), while the fifth and sixth are just outside and inside the primary arc, respectively. I’d love to see those!

Happily, in Boulder, Colorado, we do get more than our fair share of bright rainbows. I checked my pictures from the magnificent double rainbow we had the other day (the one where I got the super-lucky shot of lightning going across it!) and played with the contrast, brightness, and color saturation. I didn’t see the fifth and sixth order bows, but now that I know they can be there, I’ll keep trying for them. And at least I got this fun, if garish, shot out of it.

Enhanced colors make this rainbow picture a bit gaudy, but I kinda like it.

Photo by Phil Plait

And the next time I’m in a plane looking out the anti-solar window, I’ll keep my eyes open for more than just glories

Sept. 16 2014 7:30 AM

A Galaxy of Tatooines

Using an old-style observing technique, astronomers have come to a very interesting conclusion: About half of all exoplanets in the galaxy are in binary star systems.

That’s astonishingly cool. Mind you, it’s not unexpected, but now we have some evidence for it.


Here’s the deal. We know that roughly half the stars in the galaxy are in binary systems, with two stars physically orbiting each other. The circumstances that give rise to star formation make it pretty easy for two stars to form near each other (the Sun, of course, being an exception).

We also know that planets are pretty common around stars as well; we know of nearly 2,000 such exoplanets at this point, and thousands more are waiting to be confirmed. It’s natural to put these two ideas together, and ask: How many exoplanets orbit a star in a binary system?

You’d expect the ratio to be the same, but Nature is tricksy sometimes, so it’s best to check. However, that can be tough. Even though a binary companion might orbit a star billions of kilometers out, from light years away the two stars blend into one blob. Even Hubble might not separate the two.

To see what they could see, the astronomers relied on an old method called speckle interferometry. Basically, the Earth atmosphere roils over our heads, with little packets of air flying this way and that. When light from a star passes through them, it gets bent this way and that as well due to refraction. This happens many times per second, so when you take a long exposure the light blurs into a disk. Astronomers call this (confusingly) “seeing.” It’s also why stars appear to twinkle.

But there’s a way around this. Over time the light rays get smeared out, but if you take lots of extremely fast exposures, you freeze that motion out. It’s like taking super slo-mo video. Instead of a big disk, you get a bunch of near-perfect images of the star that jump around in location from image to image, but each frame is a nice, extremely high res shot of the star.

There are limitations to this technique; the star can’t be too faint, or else you won’t get enough light in each frame. There are also limits to the resolution due to telescope size, too. And you need a very sophisticated technique to combine the resulting frames to tease out all the information in them. But speckle interferometry has been around a long time, and its methods are solid (here’s a detailed and technical description).

The astronomers observed a bunch of stars known to have planets (found by the Kepler mission), and then used speckling to see how many had detectable stars very close by. They then used some pretty nifty simulations to find out how many binary companions they might miss—some might be too close to the star to separate even using these techniques. By comparing the two results, they were able to conclude that 40–50 percent of all exoplanets orbit a star in a binary system.

That’s pretty amazing. There are billions of planets orbiting stars in binary system in our galaxy!

What I find most interesting about all this, oddly, is the mundanity of it. Back in the day, we didn’t even know if other planets existed. Was there something special about the Sun that allowed it to host a solar system? Size, chemical content, position in the galaxy? But now we see that a wide variety of stars have planets. Even having another star orbiting the host star doesn’t seem to be a problem!

... well, as long as the other star is far enough out. Closer in, and its gravity could disrupt the planet orbit. But if the stars are close enough together, a planet could orbit both stars. Quite a few such circumbinary exoplanets (I love sciencey words) have been found. I’ve written about a few of them, like Kepler 16b and PH-1b.

Forty years ago this picture was science fiction. Now … well, now not so much.

Tatooine double sunset
Cue the french horn and the wavy hair.

Photo from LucasFilms

Sept. 15 2014 11:00 AM

The Comet and the Cosmic Beehive

In mid-October, the comet C/2013 A1 (Siding Spring) will have a very close encounter with Mars. It will pass just over 130,000 km from the Red Planet; while engineers have been working to make sure our spacecraft are safe from debris, scientists are eager to gather data about the comet using those same spacecraft.

In the meantime, the comet has become a favorite for astrophotographers, because it’s relatively bright and has been passing by one astronomical gem after another. Marco Lorenzi is one such astrophotographer. He has a remotely-operated observatory outside of Coonabarabran, Australia, and on Aug. 30, 2014, took this stunning shot of the comet as it passed by one of the most beautiful objects in the sky: the globular cluster 47 Tuc.

Sept. 15 2014 7:30 AM

Polar Vortex Excursions Linked to Global Warming

Over the past year or so, I’ve written a few times on how the “polar vortex”—actually, deep meanders or excursions in the usually stable west-to-east direction of the polar cyclonic air stream—may be tied to global warming, but there hadn’t been enough research done yet to be sure.

Well, here we go: A team of Korean and American scientists has made the connection. Warmer waters lead to more melting of Arctic ice, which destabilizes the polar jet stream. My Slate colleague Eric Holthaus has an excellent write-up of it, and I wanted to give him a signal boost here. Go read it.


I want to add a few points. One I already made above: What people have been calling the “polar vortex” is not really the polar vortex. There is a stable flow of air (that’s the polar vortex) going around the poles, at higher latitudes than the jet stream. Technically a cyclone, it wanders and wiggles from a perfect circle, but sometimes will have deep excursions, bringing frigid Arctic air to lower latitudes. Those excursions are what hit the U.S. several times in the past year.

When this happens, the excursions can become somewhat stable themselves. This prevents the normal circulation of air around the globe, so they’re called “blocking patterns.” That’s what was responsible for the tremendous heat wave Alaska suffered in January 2014. Over a year ago, in June 2013, Alaska had a persistent high pressure system squat over the state, and the year before that a similar system caused a massive melting in Greenland.

I mentioned at the time the idea that global warming may be affecting weather patterns, and of course the denial Noise Machine kicked into gear; I got a lot of comments and tweets mocking the idea.

Now, though, we have this new research upholding that conclusion. I’m not surprised. We know that global weather patterns depend on a lot of factors, but the amount of available heat—thinking of it as fuel might help—is a critical one. If you crank up the planet’s thermostat you don’t just make the climate hotter, you make it unstable.

It’s like driving a car. A lot of factors have to balance for a safe drive: how much gas you give the engine, friction with the road, road surface conditions, weather, and so on. Step on the gas and you don’t just go faster; all those factors play in, and it gets harder to control the vehicle. A small gust, a slick patch of highway, a pothole—their effects all get amplified. When you hit the gas too hard you’re in for a very terrifying out-of-control ride.

And here we are, pedal to the metal.

So while the Mail Online and Wall Street Journal continue to post ridiculous denier talking points, the world continues to heat up. I’ll note that the U.S. has done almost nothing about this, and that is almost entirely due to Republicans in the House and Senate. I’ll also note we have an election coming up, a very important one. Get the facts (I suggest starting here and here), and keep them in mind when you hit the polling booth this November.

Sept. 14 2014 8:00 AM


Hot on the heels of the incredible volcanic explosion video I posted recently comes another in the “holy cow these things really exist?!” department: a volcano tornado.

Yes, you read that right. OK, technically, it’s a vortex, more like a dust devil than a tornado. Still.


Nicarnica Aviation is a company that has created infrared cameras that can detect volcanic ash in the air as a safety measure for pilots; ash is composed of microscopic particles of rock that are very jagged, and can clog airplane engines. Wanting to avoid that while you’re in the air should be obvious enough.

One of Nicarnica’s cameras was set up near the erupting Bardarbunga volcano in Iceland, and on Wednesday, Sept. 3, they caught the hephaestean twister:

That’s amazing. It’s also not entirely unprecedented! In February 2014 a series of twisters arose from pyroclastic flows blasting down the slopes of the volcano Sinabung in Indonesia, and they’re also somewhat common in big fires (like here and here). In April, a fire in Australia generated an amazing one that lasted for quite some time.


This is the first one I’ve seen over lava, though. I suspect the physics behind it is the same as the others, though. As I wrote before:

Now technically these aren’t tornadoes, even if they look like it. Tornadoes are when a funnel cloud is connected to the ground at its bottom and the base of a cumulonimbus cloud at its top. They form from the top down, dropping from the cloud base.
In this case, though, the phenomena are built from the ground up. The pyroclastic flow [Or in this current case, lava] heats the air over the ground, causing it to rise. Air from the sides then rushes in to fill the partial vacuum. This creates swirls, eddies of turbulence, which can get amplified into the vortices seen in the video (and also in fire tornadoes which are also seriously a thing). This makes these events more like a dust devil than proper tornadoes. Or, I suppose, an ash devil. But still, yeesh.

In this case, the volcanado (yes, I’m calling it that, and yes, SyFy: Call me) is loaded with ash noxious gases like sulfur dioxide. Nasty.

fire tornado
A fire tornado was caught on video in Australia. Click to vortexenate.

Photo by Chris Tangey, from the video

But also amazing. I think this technology to spot the ash is important, too. Iceland is situated upwind from much of Europe, and as we learned in 2010 with Eyjafjallajokull, that can cause quite a mess with air travel.

For current info on the Bardarbunga volcano, I suggest the Iceland MET office website. There’s also live webcams set up (like here and here) with some pretty spectacular views.

Tip o’ the caldera to New Scientist.

Sept. 13 2014 8:00 AM

Breakaway +15

As I do every year on this day: Wear flared off-white polyester pants, go outside, face where the Moon used to be before it blasted out of Earth orbit, and pour out a drop of wine on the ground for the 311 lost souls of Moonbase Alpha.

I can’t believe it’s been 15 years now. I miss seeing Eagles soaring in the sky above.

Sept. 12 2014 7:30 AM

Rosetta’s Comet Sprouts a Jet

The European space probe Rosetta has been hanging out with the comet 67/P Churyumov-Gerasimenko since early August. Initially at station-keeping about 100 kilometers away, it’s now dropped down to less than half that. In November it’ll release the lander Philae to set down on the comet, and scientists are deciding now just where to put it.

In the meantime, Rosetta is snapping away, taking a lot of pictures and data. And the comet hasn’t been quiet: A jet of gas has formed coming from the neck region!


That image above was put together by my friend Emily Lakdawalla, and I leave it to her capable keyboarding to describe how she made this image and to give details of the science.

However, I want to add that the jet is very interesting. ALICE, an ultraviolet detector on board Rosetta, has been taking observations and found very little water ice on the surface of the comet. That’s a bit surprising, since we know comets tend to have lots of ice in them. However, ALICE did see oxygen and hydrogen surrounding the comet. That means there’s water ice under the surface, and it’s getting out. I have to say, that jet seems the likely source.

Unlike asteroids, the surfaces of comets constantly change, especially when they near the Sun. It gets warm enough to turn ice into gas, which then blows away in jets and forms the fuzzy coma surrounding the solid nucleus. That’s why the surface of Chu-Ger doesn’t look like an asteroid; the impacts aren’t as obvious when the outer layers get resurfaced all the time. Also, the comet isn’t solid, like a chunk of rock, but more likely crunchy. Impacts won’t leave your more typical-looking craters in that sort of material.

This is all very exciting! We’ve flown missions past comets before, many times, but this is the first time a probe has stuck around. The comet is slowly approaching the Sun in its orbit, and will reach its closest—and therefore warmest—point in its orbit around the Sun next August. Rosetta’s mission isn’t scheduled to end until a few months after that, so it’ll ride the comet down and watch as activity returns to this dirty snowball. And we get to ride along and watch the whole time too.

Sept. 11 2014 11:15 AM

“What If” You Just Bought This Book?

Tl;dr: Buy this book.

I’ll make this easy: If you’re a fan of my friend Randall Munroe’s xkcd Web comic, then you want to buy his new book.


If you’re not, then I suggest you read a couple of posts I wrote about his stuff—his TED talk and his epic comic “Time.” Good? Good.

Randall started a second Web comic–like series called “what if?,” where he answers readers’ weird questions by extrapolating the science as far as (and, many times, quite a bit farther than) it will go. The answers are always entertaining, funny, and display a sort of naked curiosity on Randall’s part I really admire.

So with all that, I was of course happy he decided to take the best ones and compile them with all new ones to create a book called What If: Serious Scientific Answers to Absurd Hypothetical Questions (available in hardcover and on Kindle). It’s loaded with really great stuff, including:

  • What happens if you pitch a baseball at 90 percent the speed of light? (bad things)
  • What happens if you had a mole of moles? (also bad things)
  • What would happen if a glass of water were literally suddenly half empty? (sorta bad things)
  • How fast can you hit a speed bump and still live? (pretty fast)

… and tons more.

Look, I answer questions for a living, too, and Randall is really, really good at this. He finds weird little scientific ways to answer the questions, but it’s his extrapolations that kill me. I laughed a lot reading this book. Even better: I learned stuff reading this book. And you will too.

So stop reading my blog, buy the book, read it, and then start reading my blog again. In that order. Go.