Bad Astronomy
The entire universe in blog form

June 3 2015 12:54 PM

Do Toilets Really Flush the Opposite Way in the Southern Hemisphere?

Does water drain in different directions in different hemispheres?

You’ve almost certainly heard about this before. The idea was used as the basis for an episode of The Simpsons, about toilets flushing the opposite way in the southern hemisphere.


I’ve also written about this many times, including in my first book Bad Astronomy, and also here on the blog. In the latter case, it was about debunking fraudsters tricking tourists at the Equator about the effect.

Here’s the thing: This effect is real. It’s called the Coriolis Effect, and is due to the Earth’s rotation. I have an explanation of how it works on that debunking page linked above. The Coriolis Effect is why cyclones rotate, and why they also rotate in opposite directions in the northern and southern hemispheres.

So it's real, but does it work on smaller basins, like a sink or toilet? The effect is very small, so it’s most noticeable over large areas... and it turns out to be far too small to practically affect your toilet and sink on an everyday basis. Worse, toilets don’t just drain; the water is usually injected into the bowl at an angle, which completely overwhelms the tiny Coriolis effect. Sink drains and basins can have imperfections in them that can also influence the spin of the water.

But what if you controlled for all those effects? Could you see the Coriolis effect over something as small as, say, a kiddie pool?

Yes! And my friends Destin from Smarter Every Day and Derek Muller from Veritasium went to great lengths to show it. Very great lengths: literally opposite sides of the Earth.

They set up identical pools, one in the US and one in Australia, and drained the water from them. They created two videos, meant to be seen side by side. For best viewing, go to Smarter Every Day, but here are the two videos below, stacked vertically. You’ll have to synch them, and they give instructions on how to do that.

Isn’t that wonderful? And very well done. Although it’s not obvious in the video, they repeated their experiments several times, and got the same result every time.

I could nitpick, and say that to be completely thorough, they should swap the pools, taking the northern hemisphere one to Australia and vice-versa, to make absolutely sure there was nothing in the pools themselves causing this, but to be honest I think they’ve done sufficient work here to show what’s what.

The Coriolis Effect shaped this storm system, as seen by NASA's Aqua satellite in 2011. Click to vortexinate.

From by NASA / Aqua

This is fascinating to me. I had read that this effect isn’t strong enough to be seen on scales this small, but in fact Derek pointed me to a paper from 1969 that shows it can be done! Very cool indeed. Also, be sure to watch their explanation of how this works in the video after the experiments are completed; it’s one of the best and easily understood I’ve ever seen.

I’ll note this doesn’t really change what I’ve been saying all along: While the Coriolis Effect does drive the rotation of big weather systems, it doesn’t have anything to do with how sinks or toilets drain. Look at all the trouble Derek and Destin went to to show it at all! Clearly, the effect is so tiny on small scales that it’s wiped out by small eddies and imperfections in the basins unless you go to Herculean effort to eliminate them.

My congratulations to Derek and Destin for doing such a fun experiment! I’m flushed with pride for them.

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June 3 2015 7:00 AM

Sputtering Black Hole Caught by Hubble

Most people think of black holes as sort of the Universe’s own garbage disposal, but that’s hardly fair. In fact, they’re sloppy eaters: Matter falling in can form a huge swirling disk just above The Point Of No Return, and this disk can be incredibly hot. Think of gravity as an engine driving this material, and black holes have very strong gravity.

These disks have an awesome amount of power at their disposal. This makes them very bright — among the brightest sustained sources of energy in the Universe! — and can also whip the material inside into a frenzy. The disks have complicated magnetic fields, too, and the extremely rapid rotation of material in the inner disk can form those fields into helical vortices, like magnetic tornadoes on a cosmic scale.


This, as you might expect, can do quite a bit of violence to the surrounding area.

Material from the disk is focused by these magnetic fields, forming twin beams, jets of matter and energy that blast outwards from the black hole. Again, the forces are awesome to comprehend: Much of this material is moving outward at just under the speed of light!

Such is the situation in the galaxy NGC 3862, an elliptical fuzzball located about 260 million light years away. It has a supermassive black hole in its core, with at least many millions of times the mass of the Sun. It’s one of the very few galaxies that is blasting out a jet that can be seen in optical light (most are apparent in radio wavelengths), and the jet is clumpy. Apparently turbulence in the disk and jet cause it to sputter, ejecting blobs of matter outwards like a soap-bubble gun.

These blobs move at different speeds, and sometimes a fast one can catch up to a slow one. This has been seen in smaller jets from other astronomical objects, but it’s never been seen before in another galaxy… until now.

The image at the top of this post shows such a collision. The black hole in NGC 3862 is shown by the X, and three blobs are outlined. The galaxy was first observed by Hubble in 1992, when the jet was first discovered. It was re-targeted over many years since, and Hubble’s visual clarity plus stability over time has allowed astronomers to track the blobs in the jet. As you can see, over the years, the blob outlined in green has caught up with and merged into the one outlined in blue! It’s a rear-end collision on a galactic scale.

black hole jet
Zoomed in view of the image above.

Photo by NASA,ESA, and E. Meyer (STScI)

What will happen now? It’s unclear; the physics of these jets and the blobs inside is fierce, to say the least. It’s known that such collisions can generate shock waves with vast amounts of energy, and this could accelerate the material and brighten it even more. It’s now known just how energy is dissipated inside of these jets, and further Hubble observations over the next few years may help us understand that.

And I have to mention this bit: If you use the images taken over time (and knowing the jet is roughly 750 light years long) you can measure the speed of the blob that’s catching up to the other blob. The number you get may surprise you: It’s about seven times the speed of light.

Hey, wait a sec. Nothing can travel faster than light! What gives?

It’s a trick. Well, an illusion of perspective. This is called apparent superluminal motion, and it’s been seen many times. It comes about when an object is moving in a direction very close to but not quite directly toward you, and it’s moving very near the speed of light. The light it emits is only moving a little bit faster than the object itself, so this compresses the apparent amount of time it takes to move. If you’re curious, Wikipedia has the math written out, and the old Astronomy FAQ has a description, too (scroll down to H.08). But in the end, it’s a trick of perspective, and nothing is really moving faster than light. I expect some news articles reporting this might gloss over that, and people might misinterpret it, so I wanted to give you a heads-up.

But even without warp drive, this is a pretty cool scientific result. We’re still pretty new at observing what happens close to black holes, and the math is pretty tricky. It’s not at all understood just how these jets form! Hopefully Hubble is just the beginning; newer, higher-resolution observatories are on the horizon, observing at different wavelengths of light as well, and our understanding will grow.

The Universe is a pretty bizarre place, but we’re pretty good at reading its behavioral clues. Even when those clues are blasting out of the most terrifying locations in space.

June 2 2015 1:49 PM

NASA Orders First Round of Crew Launches from Boeing

Right now, we’re in a space launch gap. It’s been nearly four years since Americans were launched into space on an American rocket from American soil. But the gap ends soon: NASA has ordered the first launch of astronauts to the International Space Station from Boeing. The launch date isn’t set, but is likely to be in 2017.

Boeing still needs to run some tests on its CST-100 vehicle, but it’s in a virtual dead heat with SpaceX on who will be the first company to put Americans back in space.


I have the details in my biweekly column for That’s a subscription-only blog, I’ll note, but it’s totally worth it as I’ve written about before.

I’m glad to see both companies moving briskly along in this endeavor. It’ll be nice to see astronauts going to space on a rocket with the Stars and Stripes on the side.

June 2 2015 11:35 AM

Science Advice and Sexual Harassment

Science is the official publication of the American Association for the Advancement of Science, a very large and prestigious scientific organization.

They have a section on their site for career advice, with articles, a forum, and an advice column. Yesterday, they ran into a, um, slight issue with that last one.


A postdoc, presumably a woman, sent in this question:

I’ve just joined a new lab for my second postdoc. It’s a good lab. I’m happy with my project. I think it could really lead to some good results. My adviser is a good scientist, and he seems like a nice guy. Here’s the problem: Whenever we meet in his office, I catch him trying to look down my shirt. Not that this matters, but he’s married. 
What should I do? 

This is not an easy situation by any means, but there is plenty of advice I can think of. As one example, pull him aside in private and say, “Listen, I know this is uncomfortable, and you may not even be aware of it, but I’ve seen you looking at my chest on more than one occasion. This is really inappropriate, and I’m asking you to stop.” If he does it again, give him a sterner warning. If he does a third time, leave footprints on his forehead — talk to the department chair.

But that’s not the answer “Bothered” got. Her question was fielded by Alice Huang, a microbiologist and former president of the AAAS. After giving a definition of what encompasses sexual harassment, Huang wrote:

As long as your adviser does not move on to other advances, I suggest you put up with it, with good humor if you can. Just make sure that he is listening to you and your ideas, taking in the results you are presenting, and taking your science seriously. His attention on your chest may be unwelcome, but you need his attention on your science and his best advice.

Yikes. I mean, seriously, yikes.

This advice is deeply, profoundly, wrong. Put up with it because he has power over you?


Understandably, the article was taken down, and after a short period was replaced with an apology:

The Ask Alice article, “Help! My adviser won’t stop looking down my shirt,” on this website has been removed by Science because it did not meet our editorial standards, was inconsistent with our extensive institutional efforts to promote the role of women in science, and had not been reviewed by experts knowledgeable about laws regarding sexual harassment in the workplace. We regret that the article had not undergone proper editorial review prior to posting. Women in science, or any other field, should never be expected to tolerate unwanted sexual attention in the workplace.

Well stated. Short, simple, and on point. I hope the editors have a chat with Dr. Huang, and she writes a follow-up. I sent an email to Science about this (before the apology was issued), but as of right now I have not heard back.

I’m satisfied with the apology; they recognized that this advice was terrible — a woman should never have to put up with this sort of thing, especially for the reasons given — and clearly the editorial policy of the magazine supports that. Hopefully they’ll put guidelines in place to prevent this sort of thing from happening again.

As for “Bothered”, I certainly hope things work out for her. A lot of women, many of whom are scientists and have some experience in this, have written about this online and discuss her situation (such as here, and here, and especially here), and I hope she sees it.

But it’s important for men to speak up about this as well, so allow me add my own thoughts.

My advice is simple. Men: Don’t do this.

The keyword in “unwanted sexual attention” is “unwanted”. This whole thing could have been easily avoided if her adviser hadn’t done this in the first place.

And if a woman does ask you to stop doing something because it makes her uncomfortable, apologize and stop doing it. Don’t make excuses, don’t rationalize it. Just apologize, and stop. Listening to what she’s saying is critical. She knows what makes her uncomfortable, and you need to respect that.

Not to oversimplify, but a lot of this comes down to just that: simple respect. This idea applies to so much: sexism, racism, homophobia, transphobia, more generic xenophobia… there are a lot of issues plaguing us. A little compassion, a little respect; those lead to listening, and that leads to understanding. And that can go a long, long way toward making this a far better world.

Edited to add: My thanks to Amy Roth for some solid editing advice while I was drafting this. She is a staunch fighter against sexism and misogyny, a good friend, and makes cool jewelry.

June 2 2015 7:00 AM

Last Call for Hyperion

My favorite moon of Saturn — really, one of my favorite objects in the whole solar system — is Hyperion. It orbits Saturn about 1.5 million kilometers out, farther than the Cassini spacecraft usually goes, so it’s only been visited a handful of times in the past decade.

On May 31, 2015, Cassini flew past the moon at a distance of about 34,000 km, and took a series of amazing pictures of it. The one at the top of this post was taken when it was almost directly between Cassini and the Sun, so it shows a thin crescent. Hyperion’s not even close to being round, so the crescent is a bit gnarled.


Even there, you can see it’s heavily cratered. But when you see it in its full glory, well, you’ll get an idea of why I like this little moon so much:

Hyperion in color isn't all that much different than grayscale.

Photo by NASA/JPL-Caltech/SSI & Jason Major

That color portrait was put together from individual images by Jason Major. In the Saturn system, where everything is bizarre, Hyperion is the bizarriest.

You can see how potato-shaped the moon is. It’s about 360 km long, and dominated by that huge, flat crater. It’s covered in smaller craters, making it look porous like a sponge… and that’s not far from being true. Its average density is about half that of water, which is lower density even than ice! That means the bulk structure of the moon must be full of holes, like a pile of rubble.

Many of the craters have a very dark material pooling in their floors, too. Those aren’t shadows; they’re real. They’re hydrocarbons, molecules made up of carbon and hydrogen. It’s possible that was material sputtered away from another moon by micrometeorite impacts, which then fell on Hyperion.

There are so many weird things about Hyperion… and this is our last chance to investigate them, at least for a long, long time. The Cassini mission is drawing near its end, and no more flybys of this odd little world are planned. That’s sad, but we’ll be seeing a lot more of these final farewells as Cassini nears the end, and visits each of the moons one last time.

But their images will live on in the Cassini raw image archive. I suggest poking around in there, as it’s fascinating; it’s full of amazing (unprocessed) shots from Saturn, more than a billion kilometers away. Astronomers will be using it for decades, I’d wager, even if and when we send more probes to that ringed bauble.

And there’s poetry to that, from a mission that has brought us so much. Even after the spacecraft itself plunges into Saturn, the data it sent back will live on, and help us understand the world that Cassini will then be an eternal part of.

June 1 2015 12:07 PM

… Attempt No Landings There

Last week, NASA announced the scientific instruments that will be put on board a spacecraft bound for Jupiter’s moon Europa in the next decade. This is a solid mission that will map the moon in incredible detail, including making 3-D maps of the ice shell surrounding its undersurface ocean.

I’m pretty excited about this, which is why it’s the topic of this week’s Bad Astronomy Video:


I wrote about this briefly last week, and the discussion took a turn for the unexpected when I got a sharp reminder of the bizarre nature of sexism online. We can travel billions of kilometers and explore strange, new worlds, but we still have a long way to go to make ours better as well. I like to think we are smart enough and good enough to do both at the same time.

June 1 2015 7:30 AM

Ceres Close-Up

Oooo, I’ve been waiting for this: The Dawn spacecraft is now close enough to the asteroid Ceres to get nice close-ups of the battered surface!

That shot was taken on May 23, from a distance of about 5,100 kilometers. The moment I saw it, I thought, “Oh wow, those grooves aren’t grooves, they’re secondary craters!”


In the more distant shots from Dawn, long linear features can be seen across the surface. We see the same sort of thing on other bodies (most notably Mars’ moon Phobos and the asteroid Vesta) and I thought they might be stress fractures. That’s weird, since Ceres is way far away from any other large object, so it doesn’t get massaged by tides or gravity.

But this close-up shows them for what they are: long chains of small craters, certainly formed when a bigger impact splashed out debris which then fell back down onto the surface. This ejected material tends to form plumes, so when they fall back you get these radial chains of secondary craters. We see this on essentially every cratered body in the solar system.

I love when a single higher-resolution picture clears up a question. Now, hopefully, we’ll soon see the zoomed shots everyone is really waiting for, showing those white spots in the big crater. I doubt a single close-up will crack that particular nut, but I suspect we’ll know pretty soon what’s what. Are they ice? If so, how did they get there? Is Ceres leaking water from its interior, or are those impact-released ice pockets like we see on Mars?

Patience. It took Dawn a long time to get to Ceres, but now we’re there. Things’ll only get cooler from now on.

May 31 2015 9:46 AM

Space Weird Thing

I recently wrote about Thing Explainer, a book by my friend and xkcd author Randall Munroe that explains complex scientific ideas using only the most common 1,000 words in the English language (originally motivated by his flippin’ brilliant Up Goer Five comic).

As I wrote that article (also using just the 1,000 most common words), I wondered how far someone could take this idea.


Now I know. My dear friends Marian Call and Molly Lewis—geek musicians and very, very clever people—made a music video that is a shot-by-shot recreation of David Bowie’s “Space Oddity” using Up Goer Five speak.

Seriously. You have to stop what you’re doing and watch this, because wow. Here is “Space Weird Thing”:

I have a lot of smart friends, and I love them all. Go listen to more of Marian’s music, and Molly’s music, and buy all the things.

May 30 2015 7:30 AM

How to Make a Rubber Ducky Comet

Before we knew what comets and asteroids looked like up close, it was popular (at least in media) to imagine them as roughly spherical, maybe a bit lumpy.

The reality was way stranger. The first comet seen up close, Halley’s, was actually more elongated, like a rock you might find in your back yard. As we sent space probes to more of these celestial flotsam, we found most were oddly shaped, and some downright bizarre: a double-lobed bowling pin shape kept popping up. Hartley 2, Wild 2, Kleopatra (which looks like a cartoon dog bone!), and now, most recently, 67P/Churyumov-Gerasimenko, the new home of the Rosetta probe. The solid part of this comet looks like a rubber ducky, with a large, flattish lobe connected somewhat off-center to a smaller, more rounded chunk.


What gives?

I’ve written about this before. My original thinking was that these shapes are due to a slow collision by two bodies, which manage to stick together. 67P, however, has many features that look more like it was one object that has been eroding away in the middle, creating the double-lobed shape.

Now it looks like the former was more important than the latter. A new study has just been published showing that slow-speed collisions between two objects can create the shapes we see.

The researchers used three-dimensional modeling to determine how this could work, and the video above shows a representative example. A larger and small body collide slightly off-center, causing material from the smaller one to splash on to the bigger one, and slowing their relative speed. Their mutual (weak) gravity draws them together again about a day later, and they wind up sticking to each other, forming the familiar two-lobed morphology.

This also explains a peculiar layering seen in some comets, due to the splashing of material from one object to the other. It’s nice when a single model can explain more than one physical characteristic.

Collisions like this may have been common in the very early solar system, when there were a lot more objects out there; as the giant planets formed after a few tens of millions of years, their powerful gravity wound up eliminating many of those comets and asteroids (either by drawing them in and assimilating them, flinging them away and ejecting them from the solar system, or dropping them down in to the inner solar system in an event called the Late Heavy Bombardment, the scars of which are still visible on the Moon today). A collision like this would be rare now.

If this scenario is correct, then, looking at 67P, I have to think both processes are at work there. It originally formed as a slow speed collision, and then erosive processes have been at work for quite some time since. The cliffs on the smaller lobe appear to be due to cleaving or calving of the comet there, and you wouldn’t expect such large flat features after a collision.

That wouldn’t surprise me at all; a lot of the features we see in astronomical objects in the solar system today are the result of many processes, some of them ongoing. These things have been around a long time, after all, and there have been periods of fairly intense activity since the whole place formed some 4.56 billion years ago. It’s incredibly rare to find an intact, pristine time capsule from that time so long ago, and we have to be aware that, in simple terms, stuff happens. So to speak. 

If this model is true, it means that collisions like this were common (since we see double lobes so often) and that most would’ve happened a long time ago. This may be testable by examining these dog bone/rubber ducky/bowling pin objects and seeing if we can determine just when they may have assumed these shapes. If it happened right after the solar system formed, then great! If not, well, then we’ll have to modify the hypothesis or abandon it.

Such is science. We sometimes have to follow a path to a wrong idea to make sure it’s not right. But even then, it may be salvageable, and at worst we’ve learned something anyway. Science is pretty cool that way.

May 29 2015 7:30 AM

Crash Course Astronomy: Uranus and Neptune

I’m not gonna lie to you: This is the best cold open of any episode we’ve done so far. I made myself laugh writing it.

Before you comment, PLEASE READ THE FOOTNOTE ON THIS ARTICLE. And if you still feel the need to comment, remember, neither you nor I is funnier than Futurama.


About that pronunciation, this may help as well.

UPDATE, May 29, 2015: ARG! I made a mistake in the video; I said the rings of Uranus were discovered in 1997, but they were discovered in 1977. It was a typo in the original script and it somehow made its way to the video without any of us noticing. Aggravating. My apologies for any confusion.

I’ve also written about those giant storms that erupted in Uranus’ atmosphere, an odd hypothesis about why the planet is tipped over, and an interesting claim that Herschel may have seen the rings of Uranus!