Bad Astronomy
The entire universe in blog form

Jan. 22 2016 9:15 AM

Crash Course Astronomy: Everything, the Universe … and Life


Forty-eight episodes, more than eight hours of content, 100,000 words, a year and a half of work, topics ranging from quantum fluctuations to the death of the Universe, and 12 million views … finally, here we are.

The final episode of Crash Course Astronomy.

When I put together the syllabus for the show, I found it helped to be flexible as the scripts got written; galaxies got split into two episodes, as did cosmology (at least, dark matter and energy). We had 45 episodes listed for a long time, and I left one slot open Just in Case. And then, last summer, I figured out what it should cover and placed it as the final one in the series, because that’s where it should be.

So I present to you the final episode of Crash Course Astronomy: Everything, the Universe ... and Life.

I think I pretty much covered how I feel about UFOs in this episode—that is, dismissive until actual evidence shows up. If you want more, I’ve written about this before, and answered a question during a public talk about it, too.

Still, it’s fun to think about alien life, and while I wrote about it in my book Death From the Skies! (in the context of how aliens might attack us, including the likelihood of infestation of alien viruses and bacteria), it’s a rich vein, and I really enjoyed writing this episode, especially since I could include a bit about my old friend Seth Shostak.

If there’s life in space, we may know soon, whether it’s from intelligent species who want to chat, or being able to detect biological signatures in the atmospheres of exoplanets. I expect that it won’t be a big, sudden announcement like it usually is in the movies, but more of a “what have we got here” kind of thing, slowly building more evidence over time.

Either way, what a time that will be.

But my time, Crash Course speaking, is up. With a full series behind me, it’s time to move on to whatever’s next for me (I’m working on some ideas; stay tuned). And if I may indulge myself …

I want to thank everyone involved in making Crash Course Astronomy. That means Hank Green, who invited me to host; Derek Muller, who relayed the question; my editors Nicole Sweeney and Blake De Pastino; director Nick Jenkins; sound designer Michael Aranda (he scored the music based on the CC music from other series); my wonderful friend and science consultant Michelle Thaller; the folks at Thought Café for their wonderful animations; and all the nerds at Sci Show who put up with me sitting in their room muttering and eating up their Wi-Fi after we’d finish recording for the day.

My biggest thanks goes out to all of you who watched the show. I hope you got to see a bigger picture of the Universe from it, and found a new way to appreciate it.

Being a part of Crash Course has been an extraordinary honor, and one that I cherish. Thank you.

Jan. 21 2016 9:00 AM

More (and Best Yet) Evidence That Another Planet Lurks in the Dark Depths of Our Solar System

Wednesday, a pair of astronomers announced potentially very exciting news: They have found evidence that another, massive planet may exist in the outer solar system. If it exists, it is likely to have roughly 10 times the mass of Earth, maybe something like Neptune in size, and orbits the Sun on a tipped, elliptical path that never brings it any closer to the Sun than 30 billion kilometers (translation: It’s very far away).

If it exists. This is pretty dramatic news, and a lot’s going on here. So let me be clear up front: The evidence they present is indirect; that is, we don’t have photos of the alleged planet (I’ve seen social media posts and the like saying a new planet has been “discovered,” and that’s simply not true). Still, while it’s not conclusive, the evidence is pretty compelling, and to be honest I think it’s far and away the best yet we’ve seen that such a planet might exist.*

So. What’s going on?

Neptune is the most distant known large planet from the Sun. Out past Neptune there’s a huge population of icy objects on various kinds of orbits. These objects are difficult to observe because they’re not very big and they’re very far away, so they’re faint. Still, quite a few have been found. The region is called the Kuiper belt, so we call these bodies Kuiper belt objects, or KBOs.

A couple of years ago, a pair of astronomers (Chad Trujillo and Scott Sheppard) noticed something peculiar about the most distant of these objects we’ve been able to find. You’d expect them to have randomly oriented orbits, pointing in different directions. However, what they found instead is that they seem to all be oriented in a similar fashion.

The orbits of six KBOs, and the possible orbit of the alleged planet. Note how the KBOs all have roughly aligned orbits.

Drawing by Batygin and Brown

The drawing above shows the orbits of six of these KBOs (in purple), and you can see they all have their long axes roughly aligned. Moreover, several other aspects of their orbits also seem to be suspiciously similar (for people who want gory details, their arguments of perihelia are all clustered around a value of 0). This is incredibly unlikely to happen randomly.

So another pair of astronomers, Konstantin Batygin and Mike Brown (full disclosure: Mike’s a friend of mine), looked into this. There are a few ways to get orbits to align like this, but the most likely given what’s seen is—you guessed it—the presence of a massive planet out beyond Neptune. They've even nicknamed it: Planet Nine. The idea is that the objects started out with random orbits, but repeated close encounters with this purported planet nudged them into paths that all had similar characteristics. UPDATE, Jan. 21, 2015: To be clear: Trujillo and Sheppard postulated a planet in their paper, with some preliminary analysis; Batygin and Brown carried out the analysis much further.

Batygin and Brown simulated what would happen to a population of the icy objects as they got tossed around by the planet’s gravity. Then, by changing the characteristics of the planet they could try to reproduce the current orbital alignments seen.

The best fit was for a planet that never got closer than 200 AU from the Sun (1 AU is the average distance of the Earth from the Sun, about 150 million kilometers; Neptune is roughly 30 AU out form the Sun). The orbit of this planet would be highly elliptical, but it’s not clear how elliptical; that’s less well constrained. At its most distant, it could be between 500 and 1,200 AU out (75 to 180 billion kilometers). The most likely mass of the planet is about 10 times Earth’s mass (for comparison, Neptune is a little more than 17 times our mass), though it could be somewhat less or more.

Interestingly, the planet is anti-aligned with the icy bodies (again, see the diagram above that has the orbits drawn, including the likely one for the purported planet). That is, its perihelion point (when it’s closest to the Sun) is on the opposite side of the Sun from the perihelia of the other objects. The way orbital mechanics works out, this actually keeps the bodies from colliding with it; when they’re closest to the Sun the planet is far away from them, and vice-versa.

There are some side benefits of this possible planet, too; it may explain the peculiar orbits of the two KBOs Sedna and 2012 VP 113; both have perihelia that are farther from the Sun than expected. This planet would also fling objects into orbits nearly perpendicular to the other planets’, and we do see a few objects like that which are very hard to explain otherwise. It’s always nice when a hypothesis predicts phenomena we actually see.

Planet Nine from Outer Space
You are interested in the unknown, the mysterious, the unexplainable. That is why you are here. And now, for the first time, we are bringing to you the full story of what happened on that fateful day. We are bringing you all the evidence, based only on the secret testimony of the miserable souls who survived this terrifying ordeal. The incidents, the places. My friend, we cannot keep this a secret any longer.

Drawing by Mike Wong, words by Criswell

OK, so, great! A previously undiscovered planet might be out there, poking and prodding icy bodies and fiddling with their orbits. But … is it possible to even get a planet that far out from the Sun?


When the solar system was first forming, 4.5 or so billion years ago, there were probably quite a few planetary-sized objects that coalesced. But close encounters with other largish objects would’ve tossed some of them into the Sun, or out to the nether regions of the solar system, with some being ejected entirely. Right now, we have two so-called ice giants out there: Uranus and Neptune. But models of the early solar system show that more planets that size should have formed. Where are they? Gone, mostly. But maybe one, with roughly half the mass of Neptune, survived…

It could’ve been thrown out a few dozen billion kilometers. It would’ve initially been on an extremely elliptical orbit that brought it back to the inner solar system. However, over time, the gravity of stars and the galaxy itself could have altered the shape of its orbit to what it is now.

OK, so it could be out there. If it is, can we find it?

Yes again! Well, kinda.

Batygin and Brown crunched the numbers, and found where the planet is likely to be in the sky at various parts of its orbit. When it’s closest to the Sun—and easiest to find, because it’ll be brighter and moving the fastest—it’s likely to be in the same part of the sky as the Milky Way, meaning it’ll be tough to spot among the many thousands of background stars. Odds are we won’t find it then anyway, because it spends the least amount of time nearer to the Sun (because it’s moving faster). But when it’s farther away and in a less crowded region of the sky, it’s fainter and harder to spot.

That may be why we haven’t seen it yet. There have been several surveys of the sky, but none has spotted it. (I’ll note that an infrared survey by the WISE spacecraft eliminated a Jupiter or even Saturn-sized planet out to quite a distance, but one the size of Neptune would probably not have been seen by WISE.)

The planet isn’t as faint as I might have expected, ranging from a magnitude of 18 to 24 or so. That’s faint, but at its brightest it’d be visible to smaller ‘scopes, and even when it’s fainter it should be within range of upcoming sky surveys. If this planet exists, we may yet find it, and maybe in the next few years.

I feel I should note that there have been a few claims like this before, even using similar ideas, but none has really panned out. One, using an unusual alignment in the orbits of comets, was proposed in 2011. The evidence was a bit shaky, so I was always skeptical, and now I doubt this works due to the WISE survey I mentioned above.

Given all this, though, the evidence presented in this new case is much better. Again, it’s not proof, but I think it’s good enough that we need to follow up on it. More models need to be run to see what else this planet could do, effects that might help nail down both its physical characteristics and orbit. That will aid in finding it.

To be honest, this is pretty exciting. I’m cautiously optimistic. It’s good to be skeptical, but from what I can tell, this stands the best chance of being real of any idea I’ve seen so far. It’s worth a look.

And one more thing, because I can’t resist. Mike Brown was the leader of the team that discovered Eris, a large Kuiper belt object that is actually roughly the same size as Pluto. Its discovery eventually led to the International Astronomical Union’s “demotion” of Pluto to minor planet status (Mike’s Twitter handle is PlutoKiller). Whether you think Pluto is a planet or not (and I don’t even think that’s the right question), the irony of this is pretty funny. If this planet exists, it’s big, and there’s no doubt it would be classified as a planet. If Mike’s prediction works out, he’ll have both killed and discovered the ninth planet.

In that order.

*Geez, I hate to even have to say this, but I know a lot of crackpots will run away with this announcement—so: This has nothing to do with Nibiru, a silly conspiracy-theory-based non-existent planet that I’ve had to spend way too much time debunking multiple times in the past. Read that link if you’d like, but I won’t spare this another thought here.

Jan. 20 2016 11:30 AM

See Five Naked-Eye Planets in the Sky at the Same Time!

If you get up very early over the next couple of weeks, there’s a treat waiting for you outside: All five naked-eye planets known since antiquity are visible in the dawn sky at once.

This is actually pretty cool, and it’s visible from anywhere in the world. Very generally, if you go outside well before dawn (5:30–6 a.m. local time) and look south (in the Northern Hemisphere; face north if you’re in the upside-down part of the world), you’ll see the planets lined up across the sky.

Mind you, that’s “very generally.” Here are some specifics:

In order from their apparent positions from the Sun in the sky, the planets are Mercury, Venus, Saturn, Mars, and Jupiter.* They scoot around a bit over the next few weeks, changing their positions and distances from each other, but stay in that order. Venus is the brightest by far, with Jupiter next. Saturn and Mars are about the same brightness as each other (compare them with the red supergiant star Antares which shines near Saturn), but Saturn will appear yellowish, while Mars will be rust-colored (because it’s rusty).

Cesar Cantu Venus Jupiter Moon
César Cantú captured this gorgeous shot of the Moon, Venus, Jupiter, and the star Regulus in July 2015. Try your hand at photographing the lineup this month!

Photo by César Cantú, used by permission

Probably the best time to go out to do this is around Feb. 1 or 2. That’s because Mercury is pretty close to the Sun right now and doesn’t clear the horizon until the sky gets light. During the first week of February it reaches what astronomers call greatest western elongation, when it’s farthest from the Sun in the sky before dawn. Even so, you’ll probably want binoculars to help you find it. It’s an irritating little planet sometimes and can hide in even thin clouds or twilight. Find Venus first, which should be pretty easy to spot, then look to its lower left for Mercury.

The planets all lie in a line because they orbit the Sun more or less in the same plane, called the ecliptic. The Earth’s in that plane, too (technically, the Earth’s orbit defines the ecliptic), so we see the other planets following that line across the sky. In the Northern Hemisphere, at my latitude of 40°, before dawn the ecliptic appears to angle away from the Sun to the upper right if you face east. But it’s different at different latitudes; near the equator that line is nearly vertical to the horizon, and in the Southern Hemisphere it tilts the other way, to the left if you face east before dawn. Folks near the equator get the best view of this event, then, because Mercury rises straight up from the horizon, so it’s up higher by the time the Sun rises and ruins the view. I talk about the motions of these objects in the sky in Episode 3 of Crash Course Astronomy:

The Moon moves around the sky far faster than the planets do and enters the scene near Jupiter on the morning of Jan. 27; over the next few days it’ll pass the planets one by one, becoming a thinner and thinner crescent as it does. It’ll be just 2° from Jupiter on Jan. 27, pretty close to Mars on the morning of Feb. 1, Saturn on Feb. 3, and then a difficult-to-spot fingernail Moon will be near Mercury and Venus on Feb. 6.

If you have a telescope, these are all fine objects to look at. Jupiter has its moons, Saturn displays its rings (and a moon or two), Venus will be nearly full, and Mercury will go from crescent to gibbous (a bit more than half full) over the next couple of weeks. Mars, however, won’t look like much; it’s nearly as far from Earth as it gets and will be very small even through a decent ‘scope. But don’t let me discourage you from taking a look! The color is still amazing to see. And of course our Moon is always a joy to see up close.

This view of the naked-eye planets isn’t common; the last time they were all visible at the same time was 10 years ago. They orbit the Sun at different speeds, like clocks all out of sync with each other, so sometimes you can see one or two together, sometimes more. This event really is a treat (and nothing to worry about doomsday-wise).

I’ll note that Pluto is very close to Mercury in the sky during this period, too. However, it’s far smaller and much, much, much farther away from us, so it’s a teeny bit fainter: Mercury is actually 400,000 brighter than Pluto in the sky right now.

And finally, of course there’s another naked-eye planet I’ve neglected to add to this list. But for that one, looking up won’t help. Look down. You’re standing on it! Bundle up, go out, look down, look up, and take in the view. It’s a good one.

*Technically, Uranus is just barely visible to the naked eye, sometimes, under good conditions. That’s why I added “known since antiquity” in the first paragraph, to ward off pedants. 

Jan. 20 2016 9:15 AM

Does Alpha Centauri Have a Planet or Not? Well …

Back in 2012, astronomers made a huge announcement: They had found a planet orbiting one of the two stars making up the binary star Alpha Centauri. This made it the closest exoplanet found—as it must be, since Alpha Centauri is the closest star system to the Sun—and not only that, it had a mass only a hair more than Earth’s.

There’s only one problem: The planet almost certainly doesn’t exist.

As problems go, that’s a big one.

Last year, a different group of astronomers examined the same data used to find the planet and showed pretty convincingly the planet is spurious, unreal. The details are complicated, but in the end it’s a product of the way the observations were made and analyzed.

The original observations used what’s called the reflex motion or radial velocity method to look for a planet. A planet orbits a star because of the star’s gravity, of course. But a planet has mass and gravity too, so while the planet makes a big circle around the star, the star makes a little circle at the same time. This means that sometimes the star moves toward us, and sometimes away. That affects its light, shifting it toward the red a tiny bit when it heads away from us, and toward the blue when it moves toward us.

As a planet orbits its star, the star moves, too.
As a planet orbits its star, the star moves, too.

llustration by NASA/Spaceplace

So if you see this periodic shift in the star light, you can detect a planet … theoretically. It’s hard to see that effect from a planet, because it can be swamped by much larger effects. Alpha Cen is a binary, so the two stars revolve around each other at hundreds of meters per second. The stars rotate, smearing out the signal. And stellar activity (star spots and the like) can also produce a similar effect as a planet.

You have to account for all these factors and see what’s left over to look for a planet, and in the end a purported planet’s signal would be very small. If any error creeps in, it can easily wipe out a planet’s signal … or make a false signal look real.

That’s what appears to have happened. The first group found a signal that looked like it was coming from a 1.13 Earth-mass planet orbiting Alpha Centauri B in 3.24 days. The second group reproduced the first group’s work and found that same signal claimed to be a planet. But what they also found was that the way the first group took and analyzed the data may have introduced the signal in the first place; it was like an echo of a real signal (for those who want gnarly details: The time between observations introduced a spike in the power spectrum of the data at 3.24 days; it’s a window function relic of taking discrete observations of a continuous series).

Mind you, this wasn’t a direct error on the part of the first group; the way they analyzed the data was fine. It was an error of omission in a way; they neglected to account for the ways their observational methods might give them false positives. One of them slipped through and made it look like a planet was there when it wasn’t.

I’ll note that not long after the original announcement was made it was called into question, but in my opinion at the time the discussion going back and forth wasn’t conclusive either way, so I waited to write anything. I prefer not to dive in when things are still unsettled in a case like this because it can be harder for the reader to follow along in the long run. I know that happens to me when I read about some medical research, for example, which gets called into question. Media report on every single bit of the back-and-forth, and after a half-dozen of those I can get confused as to what’s what.

In this case, though, the new study looks pretty solid. If I were a betting man (and really, I am) then I’d wager the planet doesn’t exist.

That, to be blunt, sucks. I was very excited when the announcement was made (I rarely use ALL CAPS in a headline), and so finding out it’s wrong is a blow. Scientifically that’s just the way things go sometimes; results on the hairy edge of what can be detected need to be examined with more skepticality than usual, and if they’re found to be spurious, well, there you go.

Still, this one hits home. I love science fiction; I’ve been reading and watching it for my whole life. Alpha Centauri is an icon, a touchstone for alien civilizations; it was used so much that in the aliens-from-Alpha-Centauri book Footfall, authors Larry Niven and Jerry Pournelle actually had their characters joke that an invasion from that star is hard to believe because it’s so cliché.

I mean, c’mon: Zefram Cochrane retired to Alpha Centauri after inventing warp drive in the Star Trek mythos. So yeah, finding an actual planet there was a big deal, and so is losing it.

The good news, such as it is, is that just because these observations didn’t pan out doesn’t mean a planet isn’t there. One or both of those stars in Alpha Cen may very well still have planets, it’s just that this particular observation didn’t root them out. It’s still very much worth looking for them there. Science is full of discoveries made after false detections—this happened with the very first exoplanets ever found, in fact—and I still hold out hope that the nearest star to our own may yet still yield the closest planets to ours as well.

Tip o’ the thermal exhaust port to Brian Koberlein.

Jan. 19 2016 9:15 AM

How Turbulence Fuels the Most Violent Explosions in the Universe

In the final seconds of a massive star’s life, a lot happens all at once. But the outcome is inevitable: BOOM.

Just how big a boom depends on the details of everything going on. The core of a star is where the action is; that’s where lighter elements are fused into heavier ones, creating energy that holds the star up against its own powerful gravity. Eventually, though, iron is created in the core, and iron absorbs energy. Once enough is made, the star is doomed.

Without the release of energy to support it, the core collapses. It happens incredibly rapidly, falling at a large fraction of the speed of light. Stars spin, though, and as the core collapses that spin increases monumentally, just like an ice skater’s spin increases when they bring their arms in to their bodies. Not only that, the core has a magnetic field too, and that also magnifies in strength hugely as the core collapses.

What happens next is that … well, the star explodes. We know in general why that happens, but some of the details have been hard to pin down. And in some stars, the star doesn’t just explode: Instead of a normal supernova explosion (which, c’mon, is a ridiculously mind-crushingly catastrophic event) you get a hypernova, an extra-big explosion.

In a hypernova, the collapsing core generates a pair of beams, twin death rays that blast outward from the spin poles of the core. The amount of energy in them is beyond anything our puny minds can adequately grasp; in a few seconds they can blast out as much energy as the Sun does over its entire 12 billion year lifetime.

The problem is, no one knows just how these beams get made. The physics is fiercely complicated, and it’s hard to model just how the increasing spin and strengthening magnetic field of the collapsing core generate them.

At least, until now. A new study shows that the key to the beams being made is turbulence. This has long thought to be behind the beams’ creation, but this new work shows how it’s possible.

In a nutshell, the core of the star is layered, and rotating at different speeds. At the boundaries of these layers the different speeds of the gases create turbulence, swirls and eddies of gas. Some of these dissipate, just like sometimes a spinning cloud on Earth doesn’t quite get the kick it needs to becomes a tornado.

But if conditions are right, some of those swirls get amplified as the core collapses and the magnetic fields guide them. As the swirls get stronger, their embedded magnetic fields get stronger too, which amplifies the swirls more … this is a positive feedback loop called a dynamo. We use a similar technique to generate electricity here on Earth! The energy of the motion of the rotating gas is what feeds the dynamo.

In a flash, these swirls become highly organized, forming a tightly collimated spinning mass aligned with the core’s rotational axis. As the core collapses, the vortices focus up and away from the poles of the rotating mass, and the vast energies of the event find a conduit along which they can travel. When they do … well, like I said before. BOOM.

Most of the energy of the newly born supernova flows along these beams, eating their way out of the star, creating the hypernova, and generating what we call a gamma-ray burst, the most violent explosion known in the Universe today.

There are two things about these new results that really burrow into my brain. One is how it’s been known for some time that turbulence must be responsible for the beams being created; without it the models are never able to generate the beams. But getting it right is incredibly difficult due to the complexity of the calculations. So for years it’s been a matter of knowing what the answer must be, but not being able to prove it.

The other bit is the length of tine it takes for the collapsing gas in the center of the star to go from a chaotic, turbulent mess to a highly organized death-ray maker. In the video above, note the clock ticking: It’s measuring time in milliseconds, and the whole thing takes less than a hundredth of a second to form. Mind you, we’re talking about events spanning a region a dozens of kilometers across, deep in the heart of a star where the densities are billions of times higher than lead and temperatures are measured in the billions of degrees!

Massive stars are many things, but subtle they are not. They are so violent, so bright that they can be seen for billions of light-years, more than halfway across the observable Universe.

And now, finally, we are starting to really understand how they work. We may be stuck on this planet, but our imagination and scientific tools allow us to wander the stars, even plunge deep within them, and know how they work. That to me is incredibly uplifting … even more so in these turbulent times.

Jan. 18 2016 12:54 PM

SpaceX Almost Lands the Falcon 9 Rocket Booster at Sea. Almost

Sunday, SpaceX successfully launched a Falcon 9 rocket into space, carrying the critically important Jason-3 Earth-observing satellite into orbit. That was the primary mission of the launch, and it went smoothly and perfectly.

Not surprisingly, most people were more excited for the secondary mission, which was to bring the first stage booster back down to Earth. This went pretty well in December, when the booster was brought back down to a landing pad at Cape Canaveral, Florida.

This time, though, they had to land on a floating platform out to sea, on an automated drone ship the size of an American football field, 300 kilometers west of San Diego. Despite heaving waters with 3 to 4 meter waves (!), the booster found the platform, centered itself, came in to land … and then this happened.

Oof. Elon Musk speculated that a collet (a rotating clamp similar to a chuck on a drill that attaches telescoping rods together) on one of the landing legs didn’t secure it tightly enough. When the booster put weight on the leg, it collapsed, and down she went. The root cause may be condensation that got in there from the thick fog at launch, which then froze in the upper atmosphere. Mind you, this is speculation! I’m sure SpaceX will examine the debris very closely to see what’s what.

Like the other two at-sea landings, this one was heartbreaking close, and still an astonishing achievement. Why?

Boosting a satellite into orbit takes a lot of speed. It needs to be moving at about 8 km/sec, or nearly 30,000 kph (18,000 mph) to reach orbit. The first stage booster gets the whole rocket moving as rapidly as possible, then is dropped as dead weight. This lightens the load, so the second stage is pushing much less mass, meaning it can accelerate harder.

That first stage booster has to flip over in space, use the little bit of fuel left over to slow from more than 6,000 kph, fall back to Earth from more than 100 kilometers in altitude, find the floating platform, guide itself there using steerable fins on its sides, deploy the landing legs, then ignite the engine again to slow for the final touchdown.

It’s a freakin’ technological triumph that they can get anywhere near a landing. And as any engineer will tell you, a failure is just a lesson in the steps to getting it right. Yes, this didn’t work, and the booster exploded. But once the reason for that is found, it’ll be fixed and hopefully it won’t happen again (at least for that reason).

The booster that landed successfully in December has been examined, including fueling it up and test-firing it while strapped down. It performed well, though one engine had a fluctuating thrust (the cause of which is still being investigated). It’s hard to say how much work will go into reusing these first stage boosters, but given they cost $60 million to build from scratch, reusing them will save a big chunk of launch cost. That’s why I’m so excited for this work. Reducing launch cost means making access to space easier, and that’s incredibly important.

And again, don’t lose sight of the successful launch of Jason-3, which will measure the effects of climate change on sea level rise and ocean currents. We have another set of eyes in the sky observing our planet, and the more of those, the better.

Jan. 18 2016 9:15 AM

I’m STILL Not Sayin’ Aliens. But This Star Is Really Weird.

OK, this is getting pretty weird.

First, a little background: You’ve probably heard of the star KIC 8462852 (though maybe by it’s nickname, Tabby’s Star, after Tabetha Boyajian, the woman who led the team that discovered its behavior). It’s the star that got a lot of press late last year because it was acting funny. Astronomers poking through the observations of the star by the Kepler spacecraft found it was undergoing a series of apparently random dips in brightness. Some of these dips were serious, with the amount of starlight dropping a staggering 22 percent.

That’s a lot. It couldn’t be a planet passing in front of the star, because the dips weren’t periodic, and the amount of starlight blocked is different every time. Plus, even a planet as big as Jupiter (which is about as big as planets can get) would block less than 1 percent of the star’s light at best.

In the original paper, Boyajian and her team make a good case that the dips are not caused by some odd thing going on in the data themselves or in their analysis of them. Whatever is going on, it’s real. They go through a bunch of possible scenarios that might be causing the dips and wind up eliminating most of them. The most likely scenario, they conclude, is that there is a huge family of comets orbiting the star, and some of them collide to create huge debris clouds that block the starlight. As I explained in my original post, that explanation has problems, too.

Belt of Dust
Debris left over from comet collisions does a decent (but not complete) job of explaining the Kepler observations. But those aren't the ONLY observations...

Artist drawing by NASA/JPL-Caltech/T. Pyle (SSC)

That left some speculation about, um, aliens. While it’s incredibly unlikely, it does kinda fit what we’re seeing. An advanced civilization would have big energy requirements, and it would make sense to build huge structures around their star to capture as much light as possible for solar power. The dips in light we see are then these “megastructures” passing in front of the star (some people call this a Dyson swarm, a collection of enormous solar panels enclosing the star).

Because why not, some follow-up looking for alien signals was made, but no dice. That’s not terribly surprising. The idea that this is all due to aliens is a bit, um, out there.

But still, the star is weird. And we just found out it’s even weirder than we thought.

Bradley Schaefer is an astronomer at Louisiana State University. He’s a clever fellow and has a habit of thinking outside the box when it comes to astronomical mysteries. When it came to Tabby’s Star, Schaefer realized there might be older observations of it that could help inform its study.

He found that Tabby’s Star has been photographed more than 1,200 times as part of a repeated all-sky survey between the years 1890 and 1989. Using two different methods, he examined those observations and measured the star’s brightness over time.

fading star
Tabby’s Star is fading over time. The blue diamonds are measurements made between 1890 and 1989. The solid line is a linear (straight-line) fit to all the data while the dashed line is just a fit to the starting and ending points. The gray points are from two other stars as controls; they don't fade over the same period.

Graph from Schaefer, 2016

What he found is rather astonishing: The star has been fading in brightness over that period, dropping by about 20 percent!

That’s … bizarre. Tabby’s Star is, by all appearances, a normal F-type star: hotter, slightly more massive, and bigger than our Sun. These stars basically just sit there and steadily turn hydrogen into helium. If they change, it’s usually on a timescale of millions of years, not centuries. Schaefer examined two other similar stars in the survey, and they remained constant in brightness over the same time period.

The long-term fading isn’t constant, either. There have been times where the star has dimmed quite a bit, then brightened up again in the following years. On average, the star is fading about 16 percent per century, but that’s hardly steady.

So it appears Tabby’s Star dims and brightens again on all kinds of timescales: hours, days, weeks, even decades and centuries.

Again. That’s bizarre. Nothing like this has ever been seen.

So what’s causing this? Well, think Occam’s razor. The simplest explanation is probably the best place to start, and in this case that means one thing is probably behind all this weird behavior. Schaefer looks into this in his paper and concludes that the comet family idea doesn’t explain all the behavior. It might explain the short-term dips (maybe, kinda) but are hugely unlikely to be behind the long-term fading. You’d need truly vast numbers of comets, and they’d have to be huge, much larger than reasonable. And they’d have to be slamming into each other just as we happen to be looking.

So, yeah. Unlikely.

Now, again, let me be clear. I am NOT saying aliens here. But, I’d be remiss if I didn’t note that this general fading is sort of what you’d expect if aliens were building a Dyson swarm. As they construct more of the panels orbiting the star, they block more of its light bit by bit, so a distant observer sees the star fade over time.

However, this doesn’t work well either. Why did the star dip so much in the 1910s, then regain brightness a few years later, for example? Also, blocking that much of the star over a century would mean they’d have to be cranking out solar panels. The star has a diameter about 1.6 times the Sun’s. To block 20 percent of its light would take solar panels equaling an area of over 750 billion square kilometers.

That’s 1,500 times the area of the entire Earth. Yikes.

And that’s only if they happened to place those panels perfectly between their star and us. More likely they would be in a ring or a sphere, so the actual area would be far, far larger. Several trillion square kilometers at least for a ring, and much more than that for a sphere.

That’s a heckuva long-term project.

So I’m still not saying aliens. But whatever it is behind this star’s peculiar behavior, it’s either something we’ve never seen before, something we have but that is on the extreme edge of what it can do, or perhaps more than one phenomenon acting together. I’ll admit, I’m scratching my head over this one.

The only thing I’m sure of? We need to keep observing this star. If there’s one thing scientists love, it’s a mystery.

Update, Jan. 18, 2016, at 19:00 UTC: This just occurred to me. In an earlier post I talked about and linked to an idea that the star is a rapid rotator, so it's squished through the poles. That can affect the light we see from it. If the star is also precessing—changing the direction in space where its axis is pointing—that would cause a slow change in brightness over time, too. Hmmm. I may have to email a few folks and see if this idea has some stickiness to it. EDITED TO ADD: The conversation is ongoing, but astronomer Jason Wright points out that my ideas probably don't work. Drat.

Jan. 17 2016 4:53 PM

A Game Is Lost on the Torque and Parabola of an Isotropic Disk

Over the weekend, the Green Bay Packers lost in a heartbreaking overtime (American) football game to the Arizona Cardinals. In a game filled with a lot of odd events (a Hail Mary pass to the end zone that led to a tie-making point with literally zero seconds left on the clock?!), both teams were so evenly matched that whoever won would be, really, a coin toss.


In the NFL, if two teams are tied at the end of the regulation game, they go into overtime. A ceremonial coin is flipped, and one team picks heads or tails. If they win, they get to choose either to kick or receive the ball, or which goal they wish to defend at the start of overtime.

At the end of the regulation game, the ref flipped the coin. Aaron Rodgers, of the Packers, called “tails.” This is when things got weird: The coin didn’t flip end-over-end. Instead of tumbling, it went up and down flat, parallel to the ground, landing on heads. Watch this video, especially the last ten seconds or so for a close-up.

Odd, eh? The ref immediately picked the coin up, said it didn’t actually flip, and tossed it up again. It again came down heads, and the Packers lost the toss. Because of this, the Cardinals got the choice, opted to receive, and seconds later ran the ball into the end zone for a touchdown, winning the game.

At this point, of course, there were complaints. Was the toss fair? Could the coin have been weighted? A Packers linebacker said, "… there was a little protective case that might have been weighted in the heads [sic] favor."

It’s possible, but I doubt it would have made a difference. The coin is heavy, so a bit of plastic on one side seems like it wouldn’t do much. I don’t see how that would’ve prevented it from tumbling end-over-end anyway; it tumbled fine in the second toss. Plus, landing twice on heads in a row is a 1 in 4 chance, not unlikely. And Aaron Rodgers, who called the toss for the Packers, had the freedom of choice to pick heads or tails. So it’s unlikely collusion or cheating was involved.

So why didn’t the coin tumble? I can think of a reason: physics, in the form of torque. Or the lack thereof.

Torque is a force applied to an object that doesn’t go through its center of mass. This imparts a rotational force on the object, generally resulting in a spin. In a coin toss, the upward motion comes mostly from the ref’s arm, throwing the coin up. But the ref also flicks their thumb on the edge of the coin, which imparts a torque, forcing the coin to flip end-over-end.

If the ref’s thumb were too far forward, under the coin’s center of mass, then the flick would not impart a torque, so the coin would just stay flat as it moved up and then back down to the ground.

coin toss
On the left, my thumb is under the coin's center of mass, so a thumb flick won't give it much torque. On the right, my thumb is near the edge; so an upward force is off-balance, and will cause the coin to tumble end-over-end.

Photo by Phil Plait

Is this what happened? Theoretical physics is fine, but nothing beats an experiment. I happen to have a medallion that’s solid metal, so I tried flipping it a few dozen times. I have to admit that I was never able to replicate the completely flat nonflipping motion of the coin in the video. It seems to me, therefore, it’s unlikely the ref could’ve placed his thumb so perfectly by accident.

I wondered for a moment if perhaps the thumb flick would’ve made the coin spin, like a top. This would give the coin gyroscopic motion, which would help it stay flat as it moved through the air. This is (ironically) the same idea that keeps a football oriented correctly when it's thrown; if it spins rapidly, the axis of rotation (through the long axis of the ball) points along the trajectory, and the ball doesn’t flip end-over-end.

But it seems impossible to flip a coin that way. It would have to spin rapidly, and a thumb flick wouldn’t do that.

So what happened? Well, I have a thought on that, and it’s way simpler than you might think. I’ve watched the video a few times, and while it’s not conclusive, here’s what I think happened: The ref threw the coin up, but it left his hand before his thumb could impart rotation! He flicked his thumb, but too late; he missed. The coin only had the upward force his arm, and without the thumb flick it didn’t tumble.

And for want of a torque a kingdom was lost.

Science! It’s everywhere. Even—really, especially—in sports.

Jan. 17 2016 9:15 AM

SpaceX Will Attempt a Second Booster Landing Sunday … Over the Ocean

SpaceX will attempt to launch a very important satellite Sunday: Jason-3, a NASA/NOAA bird that will measure the height of the ocean surface. The launch will be from the Vandenberg Space Launch Complex in California.

The launch window is 30 seconds long and begins at 18:42:18 UTC (1:42:18 Eastern U.S. time) Sunday. NASA TV will be covering it live (I prefer their UStream channel myself). I don’t know if the SpaceX live-stream channel will cover it, but you can check around the time of launch (live video of the landing may be difficult due to connectivity issues over the ocean). Update: SpaceX will have two live streams; one with hosts explaining what's going on, and one without

Update, Jan. 17, 2016, at 19:15: The launch was a success! The Jason-3 satellite is in a temporary orbit as I write this, awaiting a second burn to put it on the correct polar orbit trajectory. The booster landing, unfortunately, didn't go so well. With heaving seas at 3-4 meters, the rocket landed hard and according to Elon Musk broke a landing leg. The live feed went out, so hopefully video of the event will turn up soon.

Update, Jan. 17, 2016, at 19:45: Jason-3 has reached orbit! The second stage burn was successful, and the Earth-observing satellite is now in it final orbit—thus achieving the primary mission objective. Congratulations to everyone at NASA, NOAA, and SpaceX!

The primary mission will be to loft the satellite, of course, but most people will be watching because this will be the company’s second attempt to reland the first stage booster of the Falcon 9 rocket. The last attempt was less than a month ago and was a spectacular success, with the booster coming back down vertically at a landing pad at Cape Canaveral, Florida.

SpaceX drone platform
X marks the spot on the floating platform. For scale, it's the same size as an American football field.

Photo by SpaceX

Sunday’s attempt will be over the ocean, on a floating platform called “Just Read the Instructions” (the platforms are named after spaceships in novels written by sci-fi author Iain M. Banks). This is more difficult than bringing the booster back over land, because—and stop me if this is too complicated—land tends to stay still while the ocean surface bobs up and down, sometimes violently.

The decision to do an ocean versus land, um, landing rests on many factors, the most important of which is acceleration; a heavy payload needs more fuel to loft into orbit, and if it’s going to a higher orbit more fuel is needed still. That changes the logistics of where the booster can land; some fuel needs to remain after the boost stage to slow the first stage, bring it to the landing site, and then be used for the final descent.

In the case of Sunday’s launch, an environmental approval wasn’t received in time, so SpaceX had to move the landing out to sea. Incidentally, this launch marks the last for the v1.1 Falcon 9; the rest will be using the upgraded F9. AmericaSpace has more on that.

The booster from last month’s launch is undergoing testing right now; SpaceX CEO Elon Musk tweeted about it, indicating one of the engines underwent thrust variations during a hold-down firing test (where the booster is fueled up, strapped down, and allowed to fire its engines). Musk speculated it might have gotten some debris in it, but further testing is planned.

The point of relanding the booster is that it costs about $60 million to build the Falcon 9 first stage from scratch, but far less to load it back up with fuel and reuse it. The cost savings can then go directly into lowering the launch price. If this works, it could revolutionize rocket launches … but there are many steps to take before then, including getting a successful launch of a reused booster. That may happen this year.

Artwork depicting Jason-3 over the Earth.

Drawing by NASA

Mind you, again, the primary mission is to launch Jason-3, the latest in a series of Earth-observing satellites that will monitor how the changing climate is affecting our planet, specifically sea level rise and ocean currents. Jason-3 will use radar altimetry—bouncing radar pulses off the ocean surface and back up to space—to determine its altitude with an accuracy of a few centimeters. It will do this millions of times all over the planet, building up a detailed map of sea level over time. As polar ice melts and the oceans absorb heat from the atmosphere, the sea level is rising by over 2 millimeters per year. The ice melt introduces huge amounts of fresh water into the salty ocean, which can change ocean currents as well. All of this needs to be monitored very carefully, since the ocean currents are the major way heat is transported around the planet.

So there’s a lot riding on this launch. Let’s hope it goes off as well as the last one! If there’s a delay, the next window opens on Monday at 18:31:04 UTC.

Jan. 16 2016 9:30 AM

One of the Single Weirdest “Lights in the Sky” Events Ever: City Map Drawn in the Sky

Look at that picture!

Seriously, this is one of the single most amazing optical phenomena I have ever seen, and I’ve seen a lot of weird stuff. It was taken on Jan. 13, 2016, by Mia Heikkilä in Eura, Finland, and I’ll admit it took me a moment to figure out what it was. When I did, literally, my jaw dropped.

So. What the heck is that thing?

It’s a light pillar. Or, more accurately, a lot of light pillars, and it’s probably the most striking example of them ever. This is terribly cool, so bear with me here a sec.

Light pillars are an optical phenomenon caused by ice crystals suspended in the air. These crystals can take on a variety of shapes as water freezes, but a common one is a flat, hexagonal crystal. They’re heavier than air, so they fall, but if they’re the right size (bigger than about 20 microns across, 1/5th the width of a typical human hair), they fall slowly and stay oriented flat, parallel to the ground. As one website put it, think of it like a flying saucer landing.

Light hitting the flat sides or bottom of the crystal gets reflected. If the angle between the source, the crystal, and the observer (you) is just right, you’ll see that light reflected right at you. Here’s a diagram I drew to illustrate this:

light pillar diagram
The geometry of the light pillars, drawn with extraordinary skill.

Drawing by Phil Plait

The light reflecting off the crystals leaves at the same angle it hits, so only certain crystals will be at the right distance and height to reflect the light directly toward you. This creates, from your viewpoint, a vertical ray of light directly above the position of the source. If the crystal isn’t in the right position (say to your left or right), you don’t see the reflected light because the angles are wrong.

This is what causes a Sun pillar, a vertical column of light directly above the setting Sun. I saw one of these once … I think; I’ve never been able to confirm it, though I do think that’s what was going on.

Pillars can also form over any bright, compact source of light. Streetlights, houses, anything like that can also create these pillars. I wrote about a photo of this taken by Francis Anderson during a lunar eclipse that was quite pretty. It was that photo (and one posted on APOD a few years back) that gave me what I needed to understand the remarkable photo at the top of this article.

light pillars with city map
One map looking up, one map looking down.

Photo by Mia Heikkilä, used by permission

What you are seeing are light pillars caused by lights in the city of Eura, Finland. Streetlights, buildings, what have you; each cast their luminance upwards, where they hit widespread hexagonal ice crystals in the air, and the light was reflected back toward Heikkilä. This created a light pillar for each source, separated because of their physical separation on the ground. Due to perspective, ones that were closer to Heikkilä made smaller dots in the sky, while ones farther away made columns.

The result? A map of the city projected vertically into the sky! And it’s reversed due to the crystals reflecting the light, together with Heikkilä’s viewing angle. You can actually trace the streets in the sky using the lights as a reference. Incredible.

I’m still a bit slack-jawed thinking about this. The reversed map is amazing enough, but the perspective effect adds a depth to it that’s truly other-worldly (it’s the same sort of effect that causes what’s called a corona in an aurora as well).

Can you imagine? What it must have been like to walk outside and see this fantastically detailed and highly structured phenomenon etched across the sky?

I’ve seen fireballs blazing through the heavens, rockets re-entering, all manners of transits and eclipses and rare phenomenon, because I spend a lot of time outside looking up. But I have never, ever seen anything like this. It’s so rare I suspect I never will … so I’m glad Heikkilä was there to get these photographs.

The sky is full of wonder and surprise. Don’t forget to look up at it every now and again.

Tip o’ the lens cap to Timo Jousimo and Pasi Jokela.