Bad Astronomy
The entire universe in blog form

Aug. 27 2015 10:00 AM

Bubbly Hurricane

I used to play a lot with soap bubbles. Long after I grew up, I mean.

Scientifically, they’re very interesting; they explore such topics as thin film surfaces, optical interference, least-area surfaces, shape packing, and all kinds of chemistry.


Also, they’re pretty and silly and fun.

But one thing that never occurred to me in all that time is that soap bubbles make a pretty good stand-in for hurricanes. It might surprise you that such a delicate and fragile structure might analogize one of the most powerful and destructive events on the Earth’s surface, but sometimes in science scale isn’t a problem. It doesn’t matter if it’s small or big, the interacting forces are what matter.

My friend Dianna, aka Physics Girl, explains in this great video:

Dianna’s a great science communicator; she has a knack for making complex issues simple, but not too simple. You should check out her other videos, especially this one on mirrors flipping right and left (… or do they?), and this one on vortices in swimming pools.

Bubbles are a lot of fun, and the science they show us is astonishing and beautiful. Especially, in my not-so-unbiased opinion, when they’re on the ten trillion kilometer or so scale.

As an aside, congratulations to Dianna for now being a part of the PBS Digital Studios family! They’re partners with Hank and John Green in producing Crash Course Astronomy, so I’m a big fan of them. 

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Aug. 26 2015 10:00 AM

OK, How’d That Mountain Get There?

Ceres is the largest asteroid in the solar system*. The Dawn spacecraft has been orbiting it since early this year, and a few months ago, it spotted something really weird: a 6-kilometer tall mountain just sitting all by its lonesome on the surface.

Since that time Dawn has lowered itself closer to the surface of Ceres, where it can take higher-resolution images. A new photo of the mountain has only made things weirder:


Aug. 25 2015 12:05 PM

A Sun-Diving Neighbor

I suspect that when most people think about asteroids approaching Earth, they picture them coming from deep space, out past Mars and Jupiter.

But there’s a substantial population of asteroids where the rocks spend most of their time inside Earth’s orbit, closer to the Sun. These little beasties are hard to find because they tend not to stray too far from the Sun in the sky, so they’re up mostly during the day or twilight hours.


For my biweekly column at, I wrote about a newly discovered asteroid called 2015 QM3 that is on such an orbit, swinging it past not just Earth, but also Venus and Mercury! It’s a curious object, getting close enough to all three planets that over millions of years its orbit is certainly unstable. Not many such asteroids are known (just 17!) so any time we find a new one it helps us understand the complicated dynamics of near-Earth objects.

My articles for are subscription only, but for $5 a month you get access to a lot of pretty cool astronomical info. I check it for news and interesting photos every day. You should too.

My thanks to my friend and esteemed astronomical colleague Amy Mainzer for her help with some info about QM3 … and also for announcing the asteroid in the first place

Aug. 25 2015 7:00 AM

No, There Won’t Be a Giant Asteroid Impact in September

The latest from the Here We Go Again Department: An Internet rumor has gone viral that NASA is covering up information about a giant asteroid or comet that’s going to hit the Earth in September, sometime between Sept. 15 and 28.

Let me be clear: No.


Let me be less clear but more snarky: Go look at a bull facing north. Now walk around to the south side. See what comes out? Yeah, this asteroid impact rumor.

There are a lot of reasons this story is nonsense.

  • It was on Before It’s News, a crackpot website that is to accuracy what Donald Trump is to humility. I also try to avoid getting my news from sites that leave vowels out of their name.
  • The claim that a comet more than 2 miles wide will hit the Earth in a month or two is ridiculous right away: It would be one of the brightest objects in the sky. I think someone might have noticed.
  • NASA couldn’t cover something like this up. First of all, they’re not the world’s only space agency. Second, NASA doesn’t control all the telescopes in the world. Or even really any. There are tens of thousands of astronomers all over the planet who would have seen and been talking about an object that big headed our way.
  • As Ron Baalke pointed out, NASA announced two asteroid impacts, one in 2014 and the other in 2008—both were small rocks that burned up in our atmosphere, but it shows that NASA has not covered such things up in the past.
  • Also, how many times have we heard this kind of crap from breathless pseudoscience sites? Many, many, many, many, many, many, many, many times.
  • And how many times have they been right? Oh yeah: none. None more times.

This latest in the long-running series of hoax impact claims got spread around so much that the folks at NASA felt they had to issue a debunking of their own:


I’m glad NASA went to the trouble to write and release that, but it ticks me off. People at NASA have better things to do than squelch silly Internet nonsense. That's your tax dollars at work, folks.

But a bigger reason I get angry about stuff like this is that it scares people. It really does; whenever these rumors go around, I get plenty of anxious emails and tweets asking me if they’re true. I don’t know why sites like Before It’s News and the others post fertilizer like that story—maybe it’s just for clicks, or for attention, or because they get their jollies by scaring people for no reason whatsoever.

But every time they do they are frightening people, they are wasting time, and they’re also contributing to the overall erosion of public trust in science.

And that is something we really, really don’t need.

Tip o’ the Whipple shield to Fark and @AbsolutSpaceGrl.

Aug. 24 2015 7:00 AM









Yes, a billion.





Why are we investing in Russia, and not ourselves?






For its part, Congress has asked the president why he is underfunding SLS. That’s pretty audacious, given these facts (and given that Congress actually funded SLS at levels higher than what NASA requested). Coincidentally, the amount of money cut from Commercial Crew is about the same as what we’ve been sending to Russia for seats on their Soyuz. I'll also note that at the very best, SLS won't be ready to put humans in space for four years after a commercial vehicle could. How many billions of dollars would that mean giving to Russia to cover that gap if Commercial Crew is still underfunded?


Artwork by Boeing





Aug. 23 2015 7:30 AM










Aug. 22 2015 7:30 AM

Straight Outta Physics

Oh, I love a good science pun.

This idea came to me as soon as the “Straight Outta Compton” meme started spreading. I lack actual Photoshop skills though, so I tweeted about it, and Twitter user ClockWorkSimon came to the rescue.

scattered outta compton
Don't make me walk the Planck.

Image by ClockWorkSimon and Phil Plait



Don’t get it? Well, what’s even better than a science joke? When I get to explain one*!

Scattering is a term we use in physics to describe when two objects collide, interact in some way, then head off in different directions. There are lots of different kinds of scattering, but if you want a super simple example, think of two billiard balls hitting each other and then rebounding.

Sometimes, when two objects scatter off each other, they exchange energy. The object with lower energy steals a bit from the higher energy object. This is generally expressed as velocity, so (for example) a slow moving particle hitting a faster one speeds up while the faster one slows down. It depends on the particle masses, their velocities, directions, and lots of other stuff.

It happens with particles and light, too. A high-energy photon (a particle of light) can hit an electron. The photon loses energy while the electron goes careening off at higher speed.

This kind of interaction was first discovered by the physicist Arthur Compton in 1905, and he won the Nobel for it in 1927. In his honor, we call this Compton Scattering.

It turns out the reverse works, too: Low energy light can hit a high-velocity electron, steal its energy, and turn into a much higher energy photon, like an X-ray or a gamma ray. Lots of processes in astrophysics create high energy particles: matter swirling around a black hole, particles getting batted around in supernova shockwaves, and more. When these impact light (like starlight), the photons get pumped up to X- and gamma rays, and we can detect these with our orbiting telescopes.

So now does the joke make sense? The image in the background is a map of the sky taken by the Fermi gamma-ray observatory. Some of the gamma rays in that image are from inverse Compton scattering.


Well, it made me laugh.

Even better? I mentioned to ClockWorkSimon that some of the gamma rays in the map are from inverse Compton scattering, so he inverted the image:

Sorry if this is Bohring you.

Image by ClockWorkSimon and Phil Plait

Ha! An even dorkier physics joke.

If you laughed at that picture, then congrats! You’re a physics nerd. Give yourself +π Internet points, and go read the Wikipedia entry on equipartition of energy for fun.

And if you don’t think science can be funny, the evidence is against you. I mean, maybe not in this case, but in general, yeah.

*Because the only thing funnier than a joke is explaining why it’s funny. 

Aug. 21 2015 7:00 AM

Farewell, Dione

Last week, the nothing-short-of-phenomenal Cassini spacecraft made its last close pass of Saturn’s icy moon Dione.

Yes, last. After more than a decade orbiting Saturn, the Cassini mission’s days are numbered. It will end late in 2017, after deservedly being extended twice (and having toured the Saturnian neighborhood since 2004). So, in many cases over the next few months, when it passes by a moon it will be for the last time.

And so we have a final flyby of Dione. Cassini flew past it at a distance of less than 500 kilometers on Monday, taking quite a few images, including some with a stunning resolution of just 10 meters per pixel!Though motion blurred bit, that means features as small as a house could be seen. Not bad, from a space probe that’s a billion kilometers from Earth!

Aug. 20 2015 7:30 AM

The Southern Owl

Planetary nebulae are among my favorite objects in the sky. These are gaseous shells thrown off by middle-weight stars as they die, ethereally interacting winds that form fantastic and colorful cosmic baubles.

Many are easy to see in small telescopes, so the amateur astronomer in me loves them, and the physics behind them is fascinating, rich, and intricate, inspiring the science-minded astronomer in me (in fact; I wound up studying them for both my master’s and Ph.D., and went on to analyze even more as a professional with Hubble).


I have seen images of the planetary nebula called ESO 378-1 before, but the European Southern Observatory just released a new, gorgeous, and high-resolution shot of this lovely object:

Very cool. But what are you seeing?

What we have here is a dying star. As a star ages, its core (where the heat is generated) shrinks and heats up. This puffs up the outer layers—when you heat a gas, it expands—and the gas on the surface starts to blow away in a dense, slow wind. Eventually, so much of the outer layers blow off that the hotter lower layers get exposed. The wind blown off gets less dense and much faster, catching up with and slamming into the older, slower wind.

The resulting nebula (gas cloud) is lit by the hot exposed core of the star, and glows. The shape we see depends on what the star was doing when it blew the winds. If it was just sitting there, the winds expand as spheres, and the result looks like a soap bubble.

But with ESO 378-1, the star must have been spinning rapidly. Perhaps, in its twilight years as it expanded, it swallowed up a bunch of its planets, which would have spun it up like whisking scrambled eggs. As it spun, the gas blew off preferentially along the star’s equator due to centrifugal force. This created a dense ring of gas.

When the star started to blow off the faster wind, it slammed into this dense ring and slowed down. But up and down, along the poles of the star, the gas was free to expand. It formed a more elongated, barrel-shaped object (this diagram of another such object may help you picture it). We see that barrel at a slight angle; if you look at the interior of ESO 378-1 you can see it has two circular darkish regions, the top and bottom of the barrel.

It might be easier to see that in this photo of the Owl Nebula, a planetary nebula in Ursa Major:

Owl nebula
Your face looks familiar...


See the two dark circles? Same thing. And you can see why ESO 378-1 has the nickname the Southern Owl (the original Owl is quite far north; this one is south of the celestial equator). They look very similar, and almost certainly have similar origin stories.

As for the colors, rarefied oxygen glows blue, and hydrogen is red. I suspect the red at the top is actually due to gas floating between the stars being swept up (what astronomers call, for obvious reasons, “snowplowing”) as the planetary nebula gas expands. There must be more gas above than below, so we see a brighter rim of red there. Other planetaries do this too.

I noticed that this picture got a lot of press when it was released, but most stories simply repeated the brief info in the press release. But c’mon, you know I can’t just do that. Y’all deserve to know more than that! Plus, planetaries are near and dear to me, and I love thinking about how they get all their weird and wonderful shapes. I’ve written about them many, many times, and I urge you to peruse them. They truly are amazing objects.

Aug. 19 2015 7:00 AM

A Spritely Thunderstorm From Space




