Bad Astronomy
The entire universe in blog form

March 6 2015 7:30 AM

Time and Tide: Crash Course Astronomy Episode 8

I’m fascinated by tides. Not so much the movement of the ocean, as you might think. That’s a product of tides; what I mean is the change of gravity over distance stretching things.

Say what?


Let me explain. In fact, let me explain in the latest episode of Crash Course Astronomy: Tides!

This episode was one I was looking forward to writing ever since Hank Green asked me to do the series. Tides affect everything! The length of the day, the Moon always showing one face to us, the Moon’s recession from the Earth, and yes, even the oceans’ rise and fall. These are all due to a series of interlocked steps in physical logic that starts with the simple fact that gravity gets weaker with distance. Start with that, and the rest is inevitable.

Tides affect stars orbiting each other, galaxies when they collide, and even black holes as they gobble down matter. That’s so cool!

I know the idea that the Earth has two tidal bulges confuses a lot of people, so hopefully my explanation in the video makes it clear why they both exist, and not just one bulge pointing toward the Moon. There are a lot of ways to explain this; the actual vector analysis in a nonrotating frame is the best way, but I opted not to get into that in this short, basic video. Duh.

Also? I love the graphics Thought Café did for this episode, especially the one at the very, very end. This article I wrote may help you get that joke. There is, after all, a tide in the affairs of men.

P.S. Yes, of course I’ve read Shakespeare. His work has a lot of astronomical overlap.

Correction, March 6, 2015, at 14:45 UTC: I originally misstated that this was Episode 7. Sorry about that; I forgot to correct for time dilation.

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March 5 2015 1:49 PM

Four Planets Await After Sunset

Right now, in the night sky just after sunset, you have a chance to see three alien worlds at the same time.

Venus and Uranus are currently undergoing a close encounter; tonight (March 5) they’ll be a little over a degree apart, just about three times the width of the full Moon on the sky. Below them, not far away (maybe 10° or so) is red Mars.


To see them look to the west after sunset. It’s best to wait a few minutes for the sky to get dark. Venus is pretty obvious; it’s the third brightest natural object in the sky (after the Sun and Moon). Mars is still fairly bright and easy to spot below it. Uranus, though, is just on the edge of visibility to the naked eye even from dark sites, so you’ll probably need binoculars to spot it. I found it really easy to see last night using mine.

Speaking of last night, the picture above shows Venus and Uranus when I went out to observe. In the photo, Venus is overexposed and Uranus is the dot below it. You can see that Uranus is a bluish-green, too! That’s cool. Venus is a smaller planet, but far closer—about 200 million kilometers away versus Uranus’ 3.1 billion km distance. All told, in the sky Venus looks about 10,000 times brighter than its more distant cousin. Mars, incidentally, is about 340 million km away right now. It’s also smaller than Venus, so looks dimmer, too.

All three were easily visible even in short exposures with my camera (a Canon T4i using a 55-250 mm zoom). Here’s a nice shot I got last night:

Venus Uranus Mars
Venus, Uranus, Mars, and Piscean stars.

Photo by Phil Plait

It’s a 10-second exposure, so you can see some trailing in the stars and planets due to Earth’s rotation. But Venus and Uranus are visible to the upper left, Mars below them near the bottom of the frame, and a few of the brighter stars in the constellation of Pisces. If you have a camera, give it a shot! I literally propped mine up on a table and just took a bunch of exposures at different settings. It was also -14 C out, so don’t complain.

And hey—if you count the tree in the foreground, then you can see four planets in that picture! Not bad for a quick and dirty (and cold) photo session.

I hope you have clear skies tonight. This is a pretty nice scene to see. And when you’re done, turn around! The Moon rises around 6:30 p.m. local time, with Jupiter high above it, and the bright star Regulus (in Leo) between them.

The show is all over the sky. Go look!

March 5 2015 7:30 AM

Taking a Dusty View

I do love an edge-on spiral galaxy. They look so odd!

That image above is from the Hubble Space Telescope and shows NGC 7814, a galaxy about 40 million light-years away. That makes it relatively close as galaxies go! It’s a bit like looking at a house in the next town over. Not really your neighborhood, but not a long haul, either.


The glow you see is the combined light from countless billions of stars, for the most part orbiting the center of the galaxy in a flat disk. It’s not perfectly flat, obviously; you can see it’s puffed up a bit toward the center. That’s normal for spirals; they tend to have a bulge in the middle. Don’t we all.

The dark stuff is what astronomers call dust; complex molecules loaded with carbon. If you like technical terms, it’s also called polycyclic aromatic hydrocarbon. So there you go.

Dust is created when stars are born and when they die; it gets strewn through the flat disk of a spiral, but is also clumped up in knots and filigrees in giant nebulae, clouds that are stellar nurseries.

Dust is opaque, blocking starlight behind it, so when you see a galaxy like this edge on you see it as a thin line bifurcating the galaxy’s equator. NGC 7814 is a fine example of it.

When I see galaxies like this, I sometimes wonder what they would look like if we could see them from a different angle. That’s not possible; we’d have to travel millions of light-years (quintillions of kilometers!) to change our perspective. But … sometimes nature provides. There are, after all, a lot of galaxies in the sky, tipped at all different angles. Finding one that gives us a better angle isn’t that hard.

The third way of galaxies
Life almost on the edge, baby.

Photo by ESA/Hubble&NASA, acknowledgement: J. Barrington

That’s NGC 6861, also as seen by Hubble. It’s a galaxy similar to NGC 7814, but obviously tipped to our line of sight. Here you can see the dust swirling around the center, as well as the glow of stars. It looks like a spiral, but in fact NGC 6861 is what’s called a lenticular (lens-shaped) galaxy, a sort-of hybrid between a spiral and elliptical galaxy. It has features of both, and may be the result of a collision between two midsize galaxies. NGC 6861 is in a small, tight group of galaxies, so a collision and merger between two of them isn’t far-fetched.

I love the picture; it looks like a flying saucer whizzing by. And it shows an effect I really love: See how the dust looks darker on one side than the other? The galaxy is relatively flat, and we see the dust on the near side (upper left) fairly directly. But there are lots of stars in the galaxy, and we look through them to see the far side; they’re between us and the far side, so we see their glow. This “fills in” the dark dust, making it look somewhat faded compared with the dust on the galaxy’s near side.

This is a pretty common phenomenon in slightly tilted disk galaxies; check out NGC 3521, NGC 7049, and NGC 2841 (seriously: Click those links. The images are spectacular). 

In a lot of objects it can be pretty hard to tell which side is which, but in these cases a little thought shows the way. Studying galaxies is a funny occupation. You can spend a lot of time learning all about one in particular, but you’re stuck with the way it appears. You can’t go there or change your perspective. But you can learn so much more by studying some of the thousands of other galaxies in the sky, comparing and contrasting.

And of course, they teach us about our own galaxy, the Milky Way. After all, we live in its disk, so we see it edge on as well, even as we’re embedded in it. That makes it both the easiest and hardest galaxy to study; we can see it up close, but it’s maddeningly difficult to understand it as a whole. By studying other galaxies, separated from us by such unimaginable gulfs, we wind up getting a better grasp of, quite literally, where we live.

March 4 2015 9:42 AM

Healthy Google

Sometimes, it’s the little things.

I got an email the other day from someone who works with Google, telling me some cool news: They’ve updated their search results about health conditions. They now provide information that’s curated and vetted by doctors, including the Mayo Clinic!


That’s fantastic. So, for example, when you Google “measles,” the first couple of results are (as usual) news items, then links to the Centers for Disease Control and Prevention, the Mayo Clinic, and Wikipedia. I'll note that when I dug down a few pages in the results list, there still wasn't a single anti-vax site to be seen. Nice.

Another good part is that off to the right there's added information from a database called a "Knowledge Graph" by Google (I took a screengrab, shown above). You can get more about symptoms and treatments, and under a drawing of someone with measles is this wonderful line:

A viral infection that’s serious for small children but is easily preventable by a vaccine.

Emphasis mine. That’s great. Little tidbits like that used casually—especially by Google—can go a long way toward marginalizing views that damn well ought to be marginalized. On the Google blog (linked above), they say that 1 in 20 searches are for health issues, so this update by them is hopefully going to have a very long reach.

I’ll note that Google contacted me because they saw my article about Kristen Bell advocating for vaccination. That too makes me happy. As you can imagine, the comments I get whenever I post about vaccines (in the blog comments as well as on Twitter and Facebook) are not always reality-based. It’s really great to know that Google is on the side of science. That’s not a surprise, but it’s still nice to see them doing their part. They obviously have a vast amount of leverage, and they’re using their powers here for good.

Update, March 4, 2015, at 17:00 UTC: I should note that these results are only for the U.S., and are optimized for mobile. I checked using an iPad, and they do format quite well. 

Update 2, March 4, 2015, at 20:30 UTC: To be clear, the graphic on the right is not the "Knowledge Graph"; the database is called that. I changed the phrasing in that sentence for clarity. Also, the mobile app allows you to use voice search, which is pretty cool; as I was told, it's pretty helpful if your hands are full holding a small child or you're not sure how to spell something. :) 

March 3 2015 12:00 PM

Rosetta Sees Its Shadow on a Comet

I suppose, if you want to be traditional about it, Valentine’s Day is a good time to get as close as you can to the one you love. That may be why the Rosetta space probe dipped to a mere 6 kilometers from the surface of the comet 67P/Churyumov-Gerasimenko on Feb. 14, 2015.

When it did, it saw something remarkable: Its own shadow on the surface of the comet!


I guess that means six more weeks of winter for 67/P. Of course, when your temperature is -70 C, it’s always winter.

A few weeks ago, Rosetta began a series of maneuvers that would take it very close to the comet’s surface, as well as several swings that would take it much farther away. The idea is to sample the environment around the comet in different places to see how things change.

At one point in the low pass, the Sun was directly behind Rosetta, so its shadow was cast on the surface. The spacecraft itself is a boxy shape roughly two meters on a side but has solar panels that extend 16 meters across, which is why the shadow is rectangular. It’s fuzzy because the Sun isn’t a point source—if you were on the comet looking up at Rosetta, it would only be blocking part of the Sun, so the shadow isn’t as deep where the Sun isn’t completely blocked. The same thing happens with eclipses here on Earth.

penumbra shadow
If the Sun were a point source (left) the shadow would be sharp. Instead, it's extended (right) creating a fuzzier shadow.

Drawing by ESA

You can also see a brighter halo around the shadow. That’s called the opposition effect (or opposition surge or—my favorite—heiligenschein). Think of it this way: When the Sun is off to the side, you can see objects and their shadows. But if the Sun is directly behind you when you look at the ground, the shadow of, say, a rock falls behind it, and you can’t see it. On average the scene in that direction looks brighter.

Also, there’s a peculiar property of small grains that they can preferentially scatter light back in the direction it came. If the Sun is directly behind you, that means the light gets sent back at your eyes, making the ground look brighter. Look at dewy grass in the early morning (or dust in a baseball diamond, or similar areas covered in fine particles) and you’ll see a bright halo around your head. That’s heiligenschein.

The brightness of the halo depends a bit on the size of the particles doing the scattering, and that can be used to figure out the sizes of particles on the comet’s surface. So this picture of Rosetta’s shadow is more than just cool: It’s science.

That makes it extra cool.

And the detail! The image is a remarkable 228 meters on a side, the size of a big (American) football stadium. Think of those aerial shots you see during a game, and how you can see people sitting in their seats: That’s about the same scale as this shot. The resolution in the raw data is a stunning 11 cm per pixel. That’s the width of my hand (including my thumb). Wow.

And this mission is still in the early stages. Rosetta will follow 67/P for many more months to come, studying the comet as it nears the Sun. As it does, water ice mixed in with dust on the surface will turn even more vigorously into gas, and the comet will become more active. We’ve never been so close to a comet for so long as it does this. What amazing things will we see in the coming months?

March 3 2015 7:30 AM

The World, Ceres

On March 6, the Dawn spacecraft will ease into orbit around the largest asteroid in the main belt: Ceres.

As it approached Ceres on Feb. 19, Dawn took a series of images creating this amazing animation:


Although the resolution is still a bit low—this was taken from about 46,000 kilometers away, with a resolution of about 4 km/pixel—there are some interesting things you can see. For example, the mysterious pair of bright spots stays very bright even as they rotate into darkness, finally fading once the Sun fully sets for them.

That’s quite different behavior from another bright spot. Watch the animation: When the bright pair crosses over into darkness, turn your attention to the left side of Ceres. The next bright area comes into view after a moment, and as it rotates to the right, you can see it fade quite steadily, resolving into a crater with a bright but indistinct spot in it. For many features on airless worlds (and some with air, too) how bright a feature looks depends on the angle of sunlight hitting it. That bright region fades as it spins to the east and the Sun sets for it, but the very bright spots don’t.

That’s a clue about what they are. But we still don’t know! As Dawn gets closer, and the images get better, scientists will be paying attention to details like that so they can figure out just what they heck we’re seeing.

Another really interesting feature is an as-yet unnamed basin about 300 kilometers across (seen in the image above to the lower right); to give you a sense of scale, that basin would just fit in between Washington, D.C., and New York City. As I pointed out in an earlier post, it’s very flat given its width; I’d naively think it should be deeper. After the impact the floor may have filled in with water ice (Ceres has a lot of ice; it’s cold out there past Mars), or there may have been other forces at work. The edges of the crater don’t look round, either; it looks more like a rounded pentagon. That sometimes happens when a crater’s edge falls near cracks in the surface or the explosion shock wave hits material that’s a different strength. It could also simply be an illusion, caused by subsequent impacts marring the nice circular outline and fooling our eyes. Or it could be something else entirely; I’m guessing. Hopefully we’ll find out more in the coming months.

Excluding some fuzzy Hubble images, Ceres has been little more than a dot in our telescopes for centuries. Dawn hasn’t even gotten there yet and we’re already learning a huge amount about it … and getting even more questions. Of course, that’s why science is so much fun!

And a note: Some people call Ceres a dwarf planet, others a big asteroid. To be honest, I find that all a big distraction from the main point: Ceres is a world, a fantastic and fascinating place worthy of our attention and exploration. Dawn isn’t even really there yet and look what we’ve seen so far!

March 2 2015 4:40 PM

Waterspout Scares Beachgoers in Brazil

File this under terrifying but not as bad as it looks: Around 1 p.m. local time on March 1, a waterspout formed off the coast of a beach in Recife, Brazil. Of course everyone watched it, but then things got substantially more chaotic as the waterspout headed for the beach, scaring everyone and getting them to scatter.


As you can see, it sends palm fronds and sand flying but doesn’t do a lot of damage (no injuries were reported). Waterspouts look like tornadoes, and they’re similar, but usually far weaker. Tornadoes form as air in a supercell starts to rotate, forming a localized and intense vortex that moves down from the cloud. Waterspouts like this one form more like dust devils, where a horizontal flow of air gets lifted up and maintains its rotation. Wind speeds in these so-called fair weather waterspouts—ones that form in calm weather, even if a dark storm cloud is nearby—top out at about 20 meters per second, but a tornado can easily have winds three times that speed.

Video taken from a different vantage point shows the spout while it’s still out off the coast, and you can see why people were freaked out; it does look like a tornado:

Amazing. The spout dies quickly once it’s over land; it probably couldn’t sustain the flow of warm air inward needed to maintain the spin.

While they’re weaker and tend not to do much damage, as you can see, you don’t want to screw around with them; the wind speeds are high enough to knock you down and carry debris. And some waterspouts do in fact form like tornadoes and can be much more severe. I’m glad no one was hurt here! And while the video is amazing, listen: If you see a waterspout heading toward you, it’s probably not the best idea to stop and take video. People will always take risks in weird weather situations, but I wouldn’t recommend it.

And if you see a fire tornado or an ash devil? Run.

Tip o' the beach umbrella to Clovis Tanganelli.

March 2 2015 11:30 AM

Crash Course Astronomy Episode 7: Gravity

I was traveling last week and couldn’t put up a post about Crash Course Astronomy when it came out. So, belatedly, here is Episode 7: Gravity!

Writing these episodes can be a tightrope walk. Gravity is an interesting topic; since we’re still early in the series, I wanted to go over the aspects of gravity we’ll need to talk about planets and moons, asteroids and comets. That means discussing it as a force, how it makes things move, how orbits work, and the difference between mass and weight. That also means not getting into things like how gravity curves space, and why massless photons are still affected by gravity. I mention it but don’t go into details. Think of it as a teaser for a later episode.


I wrestled over discussing how gravity is a force that accelerates things. This is part of Newton’s Second Law of Motion: A force acting on a mass will accelerate it.* The gravity of the Earth is independent of the mass it’s working on; it’s a property of the Earth itself. If you drop two objects of different weights, they’ll fall at the same rate (ignoring air resistance). My friend Brian Cox demonstrated that quite ably.

The objects will accelerate, which means that the longer they fall, the faster they’ll go. That acceleration is a property of Earth’s gravity, and will be the same for any object. Drop a ball near the ground, and it will accelerate at a rate of about 9.8 meters per second for every second it falls. After one second it’s moving at 9.8 m/s. After two seconds it falls at 19.6 m/s, and so on.

But the force it feels is different than a ball that has a different mass. That’s the weird part that can be confusing. Gravity accelerates everything the same, but if you have more mass you feel more force. When it comes to gravity, we call that force weight. Because the force is bigger we think a more massive ball will fall faster, but it doesn’t because the acceleration is the same as it is for a less massive ball.

But if you want to stop a heavier ball, you’ll have to apply more force than you would on a lighter ball. When the heavier ball hits the ground, it hits harder than the lighter one, even though they’ll impact at the same speed.

cheese balloon
The holes make it lighter.

Photo by Shutterstock/Olga Ivanova

Now, did you notice the verbal switcheroo I just pulled? I talked about the more and less massive balls in one paragraph, then called them heavier and lighter in the next. That’s sloppy (though I did it on purpose to prove a point)! In deep space, with no (or negligible) forces acting on them, they both weigh the same: nothing. But their masses are different. Wheee!

If you think you get this now, yay! Good. But here’s a test: What weighs more: a 5 pound helium balloon, or a 5 pound block of cheese? The answer may seem obvious, but explaining it isn’t all that easy.

Maybe I’ll need to make a bonus video with that. I’ll need a big balloon. I wonder if I can get George Clooney and Sandra Bullock to guest star?

*Actually an unbalanced force; if you have another equal but oppositely directed force acting on it, the object won’t accelerate. If it’s moving it’ll still move, but if it’s just sitting there it won’t start to move. See why you need to simplify sometimes? You just need to be careful that you don’t oversimplify and make things worse. That’s another reason writing these episodes can be tricky.

March 2 2015 7:15 AM

The Week in Political Buffoonery

As someone who understands science and math, I know that when you look into a particular population looking for instances of a particular behavior, sometimes those behaviors will cluster in time. You might go a few weeks with very few instances, and then suddenly see a big clump of them happening at the same time.

Of course, when we’re talking anti-science buffoonery in politics, there is a vast, vast sample size. The statistics are pretty good.


Still, last week there were a large number of forehead-smackingly nonsensical ridiculosities. Out of them all, here are three guaranteed to put a dent in your desk where your head slams into it.

1) James Inhofe Disproves Global Warming Because Snow

Sen. James “Global warming is a hoax” Inhofe (R-Oklahoma) has never met an argument against climate change too silly and obviously wrong not to repeat. Last week, he actually stood on the floor of the United States Senate, and talking about global warming, he—and I can’t believe I’m typing this—pulled a snowball out of a plastic bag and said,

I ask the chair, you know what this is? It’s a snowball, just from outside here. So it’s very, very cold out. Very unseasonal.

Yes, Sen. Inhofe, it snows, because it’s winter. The planet is warming up, but it still gets cold in the winter (at least it does for now). If your average low temperature in February is, say -10° Celsius, then it can warm up a few degrees and still be below the freezing point of water. That’s grade-school math.

Clearly, Inhofe is an Axial Tilt Denier, too. I wonder how he’d feel knowing that he has a lot in common with a Saudi cleric.

As Stephen Colbert has said, the idea that winter disproves global warming is like nighttime disproving the existence of the Sun. If you want details, Jon Stewart did a great job slam-dunking the it’s-cold-outside-therefore-no-global-warming dumbosity.

Snark aside, Inhofe’s head is quite firmly in the sand, and he’s an embarrassment to the Senate.  I hope this is his “Michael Dukakis in a tank” moment. Thank heavens another Senate member, the wonderful Sheldon Whitehouse (D–Rhode Island), took him to task for this.

2) House Science Committee Member Doesn’t Vaccinate

Speaking of dangerous rhetoric, on the House side, Rep. Barry Loudermilk (R-Georgia) took a moment in a public town-hall meeting to let everyone know he didn’t vaccinate his kids:

Great, huh? He tried to follow up later saying he’s not against inoculation, but it’s clear he doesn’t understand the issue (and by the way Jenny McCarthy says she’s not anti-vax, either). And we know Tea Partiers tend to be anti-vax as well, though it’s usually about being anti-government, not anti-science per se.

Did I mention Rep. Loudermilk is on the House Science, Space, and Technology Committee? It may be past time to change its name.

And Rep. Loudermilk, when a GOP strategist tells you to resign over something ridiculous that you’ve said, you really, really need to rethink your position.

3) A Load of Taurus

American politicians don’t hold the monopoly on anti-science nonsense. Unhappily, facing away from reality knows no country’s borders. Case in point: Tory MP David Tredinnick thinks that a lot of the U.K.’s health problems could be helped by turning to astrology.

Just go to that link and see if you can count how many logical fallacies he relies on to back up this sentiment. Have a calculator handy. In the meantime, I’ll just leave this here.

So yeah, I’m being a bit snarky, but remember, these are critical topics—the environment, public health, and the health of science itself. If these politicians are willing to dump evidence-based reasoning by the side of the road, then what else are they willing to do? And they make our laws.

It’s time to dump them. If your representatives don’t believe in reality, then next election time it’s your responsibility to show it to them.

March 1 2015 7:30 AM

Me vs. Hank Green: SciShow Quiz Show

Part of the vast Hank and John Green video empire includes SciShow, a YouTube channel that has a variety of different science shows on it, like SciShow Dose (quick videos on interesting topics), News, Infusion (longer videos, like the vaccine one I posted about recently), and many more.

They also have Quiz Show, where two sciencey-type people go head to head in a snarky contest to see who knows more science, but which in reality just shows who can guess the answer better than the other.


When I was up at the HQ last time filming some episodes of Crash Course Astronomy they asked if I wanted to be on Quiz Show, and never one to give up an opportunity to make a fool of myself on camera, I said sure. So they pitted me against the man himself, Hank, in a battle of brains. Who will win? Find out for yourself:

So, congrats, Ian! I hope you enjoy your swag. And yes, I was very pleased with myself for deducing the answer to the second question, getting it right for the right reason. SCIENCE!