Bad Astronomy
The entire universe in blog form

May 26 2015 1:15 PM

Google Doodle Celebrates Sally Ride’s 64th Birthday

Today, American astronaut Sally Ride would have have been 64 years old.

She died in 2012, but her work lives on as an inspiration to young women who want to touch the stars. Ride was indefatigable in promoting education, in promoting the need to explore space, and working to get girls more involved with science, technology, engineering, and mathematics. As the first American woman in space her place in history was secure, but she knew what this implied for her as a role model, and maximized that leverage.


Google has helped promote her message today in a series of lovely Doodles, animated images that come up when you open the home page of the search engine. This one is my favorite.

Rather self-explanatory, isn't it? There are five in total; refresh the Google home page to see them all.

Dr. Ride was immortalized when NASA named the GRAIL spacecraft impact site after her. But her legacy was secured by her own doing, by her actions. And we thank her for them.

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May 26 2015 12:13 PM

BA Video: Close-Up on a Comet

In the 1980s, humanity got its first face-to-face view of a comet when a fleet of spacecraft was sent to visit Comet Halley, which was making its first pass into the inner solar system since 1910. We got never-before-seen close-up glimpses of the nucleus of a comet, the inner solid part that creates the gigantic gas cloud and long, beautiful tail.

Over the years more probes were sent to comets like Tempel 1, Hartley 2, and Wild 2. Each is an individual, and each is weird. But all of those missions were flybys—important but brief.


But now we have the Rosetta spacecraft orbiting the comet 67P/Chuyurmov-Gerasimenko, studying it in detail and over a great length of time. We’ve learned so much about it, but also opened up a Pandora’s box of even deeper mysteries about comets in general, and this comet in particular.

The big one, in my mind, is why it and so many others are shaped like bowling pins: two separate lobes connected by a relatively thin neck of material. We still don’t know when it comes to 67P, but in this week’s Bad Astronomy Video I go over the evidence we have so far.

The Rosetta mission has a nominal lifespan of a year, following 67P as it nears the Sun and becomes more active. There’s a huge amount left to learn, but a corresponding amount we’ll also discover. And that’s one of my favorite facts about science: It’s a jigsaw puzzle with an infinite number of pieces, so the fun of exploration never ends.

For more information about comets, read my article 10 Things You Don’t Know About Comets.

May 26 2015 7:30 AM

Climate Change Denial Is a Threat to National Security

First, let me be clear about this reality: Planet Earth is warming because of human activity, because of us, and that is profoundly affecting the climate. There is no honest doubt about this; the overwhelming evidence supports it, so much so that 97 percent of climate scientists agree on it.

The effects of climate change are profound. We are already seeing more extreme weather, more powerful tropical storms, more wildfires. As the sea level rises, coastal populations are threatened, including military bases.


I have been saying for a long time that climate change is a threat to our national security, and it’s long past time to call out those who would deny this as abetting that threat.

President Obama did just this last week, in a speech at the U.S. Coast Guard Academy. My Slate colleague Eric Holthaus wrote all about this, and I strongly urge you to read that article. Obama used words like “negligence” and “dereliction of duty”:

After all, isn’t that the true hallmark of leadership? When you’re on deck, standing your watch, you stay vigilant.  You plan for every contingency. And if you see storm clouds gathering, or dangerous shoals ahead, you don't sit back and do nothing. You take action—to protect your ship, to keep your crew safe. Anything less is negligence. It is a dereliction of duty. And so, too, with climate change. Denying it, or refusing to deal with it endangers our national security. It undermines the readiness of our forces.

This sentiment was reinforced in a tweet from the president:

Take a moment and ponder this. The president of the United States of America said that people who deny the reality of climate change are a threat to national security. And he strongly implied that members of Congress who do so are guilty of dereliction of duty.

I agree. And they do so on the basis of what is at best wrong information, and at worst a passel of lies.

The only doubt is manufactured, sole-sourced by the fossil fuel industry. Senators, Congress critters, “think tanks,” sponsored by fossil fuel (and using the same tactics as the tobacco industry)—the doubt they sow is as fake as $3 bill, and just as obvious (and embarrassing). From ridiculous and patently false claims that global warming has slowed, that the world can’t be warming because winter still exists, that (seriously) plants like carbon dioxide so we’re just feeding them; these people’s only purpose is to slow any real progress on fixing the planetary mess we’re in.

And in that way, they are making things far, far worse.

As the latest example, look at an op-ed in Forbes magazine written by Heartland Institute’s James Taylor (yes, that Heartland Institute). Taylor has a history of cherry-picking and distorting results from real climate scientists, and he’s doing the same thing here.

In the op-ed, he claims that global warming has not caused global sea ice retreat. This is a gross distortion of reality. The truth is that in the arctic we’re seeing record low levels of sea ice year after year, including just this year, when in March the North Pole saw the lowest maximum ice extent on record.

Annual Arctic sea ice minima
Arctic sea ice minimum extents since 1979, when satellite measurements were started. This is the 2013 graph that I extended to add 2014's minimum. The blue line is a linear fit to the numbers. Even James Taylor could spot this trend.

Graph by NSIDC

It takes a very twisted view of the world to claim global warming isn’t doing anything to polar ice not two months after that record was broken. And as we know very, very well, Arctic sea ice is on a long, drastic decline that does not show any signs of recovery at all.

But note how Taylor phrases it, using “global” ice. That includes Antarctic sea ice, but as I have written about over and over again, that is really unfair. Antarctic sea ice is very different than at the North Pole; Antarctica is a continent and conditions there are literally polar opposites. The southern sea ice fluctuates quite a bit year to year, and in fact wind-driven snow can be increased by global warming (warmer air can hold more moisture), so glossing over local conditions the way Taylor does is at best misleading.

Antarctic ice loss
Land ice loss from Antartcica from 2002–2009. Note the scale of the graph on the left: It's in billions of tons.

Diagram by NASA

That doesn’t sound at all like what Taylor is claiming, does it? I guess he doesn’t know (or doesn’t say) that his corporate sponsors are using the ongoing decrease in arctic ice as a reason to explore more drilling sites in north polar waters.

I’ll also note Taylor links to some satellite data from the University of Illinois Polar Research Group to make his claim … and that same group has issued a rebuttal saying Taylor cherry-picked his data and refutes his claim. Oops.

As much as I loathe what Taylor is doing and saying, I reserve my strongest feelings for people like Sen. James Inhofe (R-Oklahaoma); my own senator, Cory Gardner (R-Colorado); and virtually all the GOP presidential candidates, who claim with various degrees of head-in-the-sand-ness that humans aren’t causing global warming.

These people have a sworn duty to protect the people of our nation. What they are doing is the exact opposite in every way. They cut NASA’s funding to investigate climate change. They even cut the Pentagon’s funding to act on it. The Pentagon.

head in the sand
"Maybe if I stay this way until 2016 I can get re-elected."

Photo by Shutterstock/alphaspirit

In the medium to long run these politicians are putting us at greater risk from drought, wildfire, extreme weather, and rising sea levels. In the near run they are cruelly crippling our ability to do the kind of research that has made the United States of America a world leader in scientific innovation.

They claim to love this country. But they sure don’t act that way.

I have written about the reality of global warming and the lies of the deniers so often that to list them all would be counterproductive. Instead, here are some highlights that you can use to counter the denial; check links therein to find even more.

… and, of course, always check Skeptical Science when you hear a claim from someone saying global warming isn’t real. The vast, overwhelming amount of the time, that claim is nitrogen-rich.

May 25 2015 7:15 AM

It’s Crowded Downtown

Funny. I was thinking I want to just post a big, gorgeous, colorful photo showing a bunch of different astronomical objects in one scene, and then I found an old note from Derek Demeter, planetarium director at the Seminole State College of Florida. He’s an accomplished astrophotographer, and took this stunning picture of the galactic center last October:

May 24 2015 7:30 AM

Wait. That’s the Same Comet?

The folks at the European Space Agency released a new picture of comet 67P/Churyumov-Gerasimenko, and I have to admit that it threw me.

Huh. That’s the comet? Where’s the second lobe?


For a second I thought we were just seeing it end-on, so that the bi-lobed rubber ducky shape wasn’t obvious. But then I realized the part we’re seeing is too thin; the big bottom lobe is much wider than seen here. I did a bunch of rotations and such in my head, and quickly concluded there’s simply no angle on the comet that would produce this view.

My brain really jammed at that point, and I had to concede: I didn’t understand the photo. I read the accompanying text to find out what was going on and got a good chuckle. I forgot about the Sun.

Here’s the same photo, with the contrast/brightness wildly stretched:


Photo by ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

Aha! The smaller lobe is there, a barely darker black against the black sky. The reason it can’t be seen is that it’s in the bigger lobe’s shadow. And also, the bottom of the bigger lobe is flattened, shaped more like a river rock than a potato. At this angle it looks foreshortened, so that fooled me as well.

I love puzzles, and I love getting as far as I can before going to the answer key, but this still felt a little like cheating, since I couldn’t figure it out all out by myself. Drat!

But there’s one thing I did see that I do understand. Look to the left, just below the tip of the lobe. See that luminous line dropping down? Care to guess what that is?

Hint: The plumes you see coming from the comet are actually jets of gas, caused by the Sun heating the ice in the comet, turning it directly into a gas.*

Got it now? That vertical line is the shadow of the solid part of the lobe on the gas surrounding the comet. Comets are so weird: They can cast shadows on themselves!

I’ve spent a lot of my life interpreting astronomical images, squeezing the science out of them by analyzing their shapes, contours, brightness, colors, and more. This picture is a good reminder not to take experience for granted, nor to invest too much confidence in it.

Any of us can be fooled at any time. That’s an uncomfortable but necessary piece of information to always keep in mind.

*Also making it useful for the annual Pacific Tech “Smart People on Ice” show. And yes, I did just watch Real Genius for the 300th time the other night. Why do you ask?

May 23 2015 7:15 AM

How Do Clouds Form?

As someone who loves looking at clouds, and may have a somewhat scientifically directed brain, I’m fascinated by the shapes and structures of clouds. Where I live, at the foot of the Rocky Mountains, provides endless examples of them.

I write about them a lot, but I don’t think I’ve ever explained just how clouds form. After all, it’s a little weird: A typical storm cloud can have a mass of millions of tons, yet they float! I know this is because they’re less dense than air, but that still seems weird.


But, if you watch this great video on how clouds form by my friends at Minute Earth, you’ll understand exactly how this all works.

There were two parts in that video that I want to emphasize. One was just why clouds are buoyant; it’s for the same reason a helium balloon is. At a given temperature, a volume of a gas will have the same number of atoms or molecules in it no matter what those atoms or molecules are. Helium atoms have way less mass than oxygen and nitrogen, so it weighs less, so up it goes. And it’s the same for humid air!

The other part was why clouds have flat bottoms. The video makes that really obvious: As you go up in altitude, the temperature of the air drops (this is called the lapse rate, which for some reason is a term I think is really cool). Water vapor (water as a gas) is transparent, so you don’t see that big bubble of rising humid air until it gets to the part of the atmosphere where it’s cool enough for the water to condense into droplets (and becomes visible). If the air over a wide area over the ground all reaches that temperature at the same altitude, it forms a plane parallel to the ground. As the humid air rises through that plane it condenses, forming a cloud that is round on top and flat on the bottom. It’s actually a bit of an illusion; the parcel of rising air is still balloon-shaped (very roughly), but you only see it where the water condenses.

I have to admit: I knew all the pieces of this but hadn’t really put it all together in my head all at once. Seeing it drawn out this way in animated form made it very clear (so to speak, har har).

At the top of this post is a picture of clouds forming with flat bottoms, and you can see their bottoms are all at about the same altitude. I have always thought this would explain why we see the sky as a flattened dome over our heads; a cloud directly overhead is close to us, but one near the horizon is much farther away, giving the sky a flattened look. The perspective effect is strong; you can see how the clouds appear to bunch together when they’re farther away. That’s not real; they’re probably scattered just as much 50 kilometers away as they are overhead, it’s just that when they’re farther away you see more of them in the same area of sky because they appear smaller with distance.

If all of this seems obvious to you, then yay! But I know that many times, when we live our lives in the natural world, there’s a lot of stuff we see, and even a lot of pieces of it we understand. But putting it all together, turning it from a lot of jigsaw puzzle pieces into a single glorious picture, well, sometimes you need someone to show you that part.

If you want more about clouds, then watch this other video by my pal Joe Hanson from It’s Okay To Be Smart. There’s a lot more there.

Tip o’ the brolly to the good folks (who are also friends of mine!) at Science Alert, too, for linking to both videos.

May 22 2015 2:42 PM

Dragon-Eye View of SpaceX Pad Abort Launch

On May 5, SpaceX tested its launch abort system: a set of powerful rockets on the Dragon space capsule that can pull the Dragon away from the Falcon rocket underneath in case of catastrophe.

SpaceX just released video taken from a camera on the Dragon capsule, and it’s pretty dang dramatic. Come along for the ride:


Whoa. SpaceX said the capsule went from 0 to 160 kilometers per hour in 1.2 seconds, which is an acceleration of four times Earth’s gravity. It reached a top speed of 550 kph, arcing nearly 1,200 meters into the air.

You can see the trunk jettisoned at 0:30 (in a real flight, this sits under the Dragon and contains unpressurized cargo and the capsule’s solar panels). At the time I wondered where the trunk landed after the test; from this it looks like it came down in the water; it looks to me the capsule was already past the shoreline when the trunk jettisoned.

Seconds later the drogue chutes deploy to stabilize the capsule, then the three main parachutes release. Weirdly, the video stops just before the capsule splashes down. Perhaps we’ll see more of that later.

This test was critically important: NASA requires any human-rated vehicle to pass stringent tests, including the ability to get astronauts away from the rocket stack in case of emergency. If SpaceX had failed this test, it would have been a major setback to getting Americans back into space on an American rocket. As it happens, things look to have gone pretty well.

There's also video of the test taken from cameras on the ground, and you can see just how fast the capsule blasted away from the pad. 

The SuperDraco thrusters used for this test have double duty with Dragon; besides being there if needed in an emergency, they can be used on-orbit for maneuvering the capsule. SpaceX plans on being ready to put humans into space by 2017. They are also currently building the next generation Falcon Heavy rocket with plans for a test launch later this year.

May 22 2015 7:00 AM

Crash Course Astronomy: The Lord of the Rings

Who out there doesn’t need a little more Saturn in their life? I can deliver.

This was a cool one to record. Even though we’d done 17 episodes before, I like to play with the format a little bit. I was a little more relaxed when we shot this, leaning back in the chair more and just having more fun with it. I hope that shows.


I know I’ll get asked about this, so to head the question off: Yes, Saturn’s rings really are thinner to scale than paper, by a lot. I’ve done the math.

For clarity, I’ll note that there are places where Saturn’s rings are thicker than 10 meters; they range up to a kilometer thick in some regions. But bear in mind that’s still compared to their 300,000 km diameter! That’s a heckuva ratio.

And why not: Here’s an article I wrote about what would happen if Saturn made a close approach to Earth, inspired by a very cool video showing what it would look like. You’ll like it.

As for Saturn itself, now is a great time to go out and see it. By a funny coincidence, Saturn is at opposition tonight: That means it’s opposite the Sun in the sky, rising at sunset and setting at sunrise. It’s up all night, and that also means it’s as close to Earth as it will get for the year (about 1.34 billion km). If you want to see the planet for yourself—and oh my, yes you do—the next few weeks are the best time to do it.

Find a local observatory or nearby astronomy club; I imagine they’ll have viewings. I expect some people will be thinking of buying a telescope, too, so read this first!

Saturn through a telescope can be literally life-changing. It changed mine, and it’s done so for others. Go look.

May 21 2015 12:00 PM


I’ve been listening to electronica music for a long time (like, a really long time; as in I have Isao Tomita albums), and it’s interesting to me that variations of it are still popular. I can’t keep up with kids these days (STAY OFF MY ELECTRONS), so when a publicist sent me a note about Jamie XX, well, I’d never heard of him.

But she said the video for his new song “Gosh” has cool planetary visuals, so I figured what the heck. I clicked the link, and I have to admit: Yeah, the video has stunning visuals. It starts slow, so give it a chance.


I have to admit to chuckling when the rotating arm of the spaceship swings into view fully a minute into the video, after the very long approach sequence to Mars. That was well done. And the parts with spaceships and space stations set against the planet’s limb are really beautiful. Not to mention looking down on the dunes, craters, and other landscapes. The bits at the end with water-filled craters are really, really nice, jumping into the future after the planet is terraformed. That was pretty cool.

The music isn’t exactly my cup of tea, but after listening to it a couple of times it grew on me. I have pretty eclectic taste (I’ll listen to the Captain America 2 soundtrack then ABBA then Shostakovich all without a break), but this was still something of a stretch. But I do kinda like it.

And I like that the video is slow, languid, letting you linger over each scene. It’s nice to know that some people making visual art still appreciate simple beauty and give you a chance to soak it in.

And who knows? What’s art today may very well be fact in a century or two. That’s the point.

May 21 2015 7:00 AM

The Cliffs of Churyumov-Gerasimenko

The Rosetta spacecraft hasn’t been in the news much lately, but wow, is it the gift that keeps on giving. Check out this magnificent view of the comet 67P/Churyumov-Gerasimenko, looking past the Seth region on the big lobe to the towering Hathor cliffs on the small one:

Oh, my.


67P is a double-lobed beast, a 4-kilometer-long cosmic rubber ducky. It’s not clear why it (and so many other comets and asteroids) have this bowling pin or dumbbell shape; maybe it’s from two objects colliding slowly and sticking together, or one bigger object slowly eroding away as ice inside the comet gets heated to a gas by sunlight and vents into space.

Those cliffs are a clue, but what they’re telling us isn’t clear. They reach 900 meters high and are striated with linear features, looking very much like the comet has been cleaved right there.

That view is strengthened, perhaps unfairly, when you look at the comet in context. This mosaic shows 67P taken at a different time, but viewed from almost the exact same angle, and the lower left quadrant shows the same part of the comet as seen above:

When you see the whole thing, it looks like it was a snack for Galactus.

Photo by ESA/Rosetta/NAVCAM (CC BY-SA IGO 3.0)

It really looks like it has a bite taken out of it! It’s not hard to imagine this started off as a more elongated, somewhat cylindrical object, and that over the eons a vent in the side kept getting bigger and bigger, eating away into the body of the comet.

The same as the top image, but enhanced to show the gas venting away.

Photo by ESA/Rosetta/NAVCAM (CC BY-SA IGO 3.0)

Interestingly, you can see ice doing just that from Seth; if you brighten the top image a bit and drop the contrast, the streams of gas flowing away can be clearly seen.

But all this could be coincidence; the comet is a bizarre, alien landscape, and interpretation is difficult. Our sense of what can happen there may be biased by our more terrestrial experience, and we have to be careful to remember: This is in space, has little gravity, is composed of loosely conglomerated gravel and ice, and is sculpted by escaping gas and the rare impact rather than wind and sea. It’s easy to follow the garden path of reason to a completely wrong conclusion here.

But it’s fun to think about, isn’t it?