Bad Astronomy
The entire universe in blog form

Oct. 12 2015 9:30 AM

What Really Killed the Dinosaurs?

When I was a kid, one of the all-time biggest mysteries in science could be summed up simply: What killed the dinosaurs 65-or-so million years ago? And, along with them, fully 75 percent of all plant and animal species on Earth?

In the 1980s, the idea—now widely accepted—was that an asteroid impact did the deed. It would’ve been about 10 kilometers across, and the impact so huge that it would have released the equivalent energy of millions of thermonuclear bombs. The impact event, the tsunami, the earthquakes, and the resulting gigatons of dust thrown into the air caused a massive global ecological disaster. Ejecta from the explosion would have rained down worldwide, causing fires as they re-entered from near-space heights as well. It would’ve made the sweatiest biblical apocalypse look mild by comparison.


But still, scientists have wondered. Not all the pieces fit perfectly. Yes, a crater was found off the Yucatan peninsula that matched the size and age of the impact, but it wasn’t the reality of the impact that was in question. It was the results.

Some scientists have had problems with the timing of the impact, and the damage it did. There was evidence that the extinction took longer than you’d expect from a single, large, explosive event.

Apocalyptic, yes, but it may have had help.

Drawing by Stocktrek Images Inc./Alamy

Eyes turned to the Deccan Traps. This is a vast region in India covered in multiple layers of volcanic basalts. They cover half a million square kilometers of area and, most interestingly, were dated to 66 million years ago (though the eruptions occurred over a very long time, millions of years). We know that huge volcanic events can have a profound impact on the environment as well.

Hmmmm. Coincidence? One problem: The eruption of the Deccan Traps clearly predates the extinction event. What role might it have played?

No one has really been sure. But now a team of scientists thinks they have the key to the whole thing: It was both.

They examined the rocks in the Deccan flows and using ratios of radioactive isotopes have obtained the most accurate dating for the volcanic event yet. Yes, the flows predated the impact, but right around the time the asteroid hit, the flows increased prodigiously.

deccan traps
Part of the Deccan Traps in western India. See the layering? That's not sedimentary, that's igneous rock deposition, and it goes on for more than 1,000 kilometers. This was no ordinary volcanic event.

Photo by wikipedian Nichalp, used under the CC-BY-SA 2.5 license.

Their idea is that the asteroid impact deposited so much energy into the Earth’s crust that it affected the Deccan Traps, tens of thousands of kilometers away. Basically, the impact may have temporarily increased the ability of magma to flow out through the Traps. It had been slow before the impact, but the impact cleaned the pipes, so to speak, and as much as 70 percent of the main eruption may have occurred in the millennia that followed.

The impact did the main work, but it was the increased volcanic activity that performed the coup de grâce. The gases released into the atmosphere may have delayed the recovery of the Earth’s ecosystem for as long as a half-million years. Not every animal was wiped out, of course—the avian dinosaurs survived to become birds, and small mammals made it through as well, becoming … us.

This idea of a one-two punch is pretty interesting. It answers a lot of questions, but it’s not really proven yet. It’ll be fun to see what arguments it engenders among geologists, biologists, volcanologists, and paleontologists. Scientists love to argue! But it’s because we want to find the truth, whatever it may be.

Personally, I think the idea has merit, and it does fit with a preconception of mine: It’s pretty rare in the Universe for there to be a Single Event that has some great consequences. It’s usually a combination of factors that leads to the complexity of the world we see around us. This isn’t always the case, and I certainly wouldn’t want to be led astray by the idea, but when it comes to the demise of the dinosaurs it’s very well possible that terrestrial and extraterrestrial events conspired to lay them low.

On a personal note: During a TV documentary shoot, I visited the Trinidad Park in Colorado, which has one of the world’s best displays of the iridium layer, a layer of clay with elevated amounts of iridium in it that has been dated to the extinction of the dinosaurs. It was this layer that prompted the idea that an asteroid impact killed the giant beasts. I made a short video of my visit (please excuse the wind noise!) that you may enjoy:

Anyway, this story isn’t over yet. Even though we now have a grasp on the bigger picture, there’s still much to learn. What specifically happened to do so much damage to our blue-green world? What changes were made to the atmosphere, the water, the land? And could something like this happen again?

The dinosaurs weren’t terribly bright and didn’t have science that could allow them to understand what happened to them. We do. We need to learn more about what happened to our distant brethren, because there, but for the grace of astronomy and geology, go we. 

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Oct. 11 2015 9:00 AM

Crash Course Astronomy: Star Clusters

Last week’s episode of Crash Course dealt with stars in multiple systems: binaries, triples, quadruples, and more. Most stars in the sky are multiples!

It turns out that stars can be in even bigger, more complex systems. Most stars may be born by the thousands in clusters. Maybe even the Sun was.


Clusters are gorgeous astronomical objects, but they’re more than that: They’re astrophysical laboratories, allowing us to puzzle out a lot of very cool information about the starry denizens that live there.

Want to know more? Let this guy in a fabulous shirt tell you more in Crash Course Astronomy: Star Clusters.

A caveat: At 7:30, I say that the stars in globular clusters were all born at the same time, and therefore are the same age. That’s not actually precisely really true, so much. It may be true for most globulars, but we do know of examples where star formation happened in two, separate events. This tends to happen in more massive clusters; perhaps they were so massive their gravity could draw in gas around them, triggering a second wave of star formation.

As sometimes happens in CCA, I wanted to talk about this, but it’s hard to introduce a topic like that and cover it well enough to be understood in the allotted time for the episode. I had to agonize over what to leave in and take out in practically every episode. There’s just too much astronomy!

I’ve written about globular clusters dozens of times over the years. If you’re curious, some of my favorite ones are M15, 47 Tuc, and Omega Cen.

Not to downplay open clusters! I like them too. A few of my choices are the Pleiades (duh), NGC 3603, M67 (mostly because it’s incredibly old, which is unusual for an open cluster), and the Double Cluster (h and χ Persei) in Perseus—it’s visible to the naked eye form very dark sites, shows up as a double in binoculars, and then reveals its true nature as two separate clusters when you look through a telescope. Very very cool.

Oct. 10 2015 9:30 AM

My Favorite Martian

What would it be like to walk across the surface of Mars?

Go watch The Martian, and find out. During a lot of the movie, it really felt like I was watching events unfold on the Red Planet. The scenery and photography were just that real.


Seriously, the movie would be worth the price of admission just for that (though, full disclosure: I’m a space dork). But also? It’s just a really fun movie.

I know, a lot of you are expecting me to light into the science of the movie, but I won’t bother; it’s been covered extensively (like on io9 and Vox; also NASA has a nice summary of real tech they’re working on to keep people alive on Mars).

But as I’ve said over and again, good or bad science won’t make or break a movie for me. I’m more interested in story, and if science is an important part, I’m more concerned with how it’s depicted over what’s actually shown. In The Martian, science is depicted really well for the most part, and what’s better, the people doing the science are shown actually doing it.

Spoilers from here on out, so if you want to keep your knowledge of the movie pristine, then just go see it, then come back and continue reading, OK?

The basic premise of the movie is that early on in the exploration of Mars, a team of astronauts is doing their work when a big storm rises. They have to evacuate in a hurry and wind up leaving their botanist, Mark Watney,* behind, thinking he had died. He then has to figure out how to live on Mars for more than a year with extremely limited resources and no help from Earth. His only hope? Science.

The Martian
Watney is a botanist, but he needs to understand science like chemistry, biology, physics, and engineering if he ever wants to see home again.

Courtesy of 20th Century Fox

There are no aliens in this flick, no faster than light travel, no sci-fi gimmicks. It’s all based on real tech, real extrapolation, and even if some Hollywood shortcuts are taken, they don’t change the basic level of reality to the movie.

In fact, I’d say science is every bit the protagonist of this movie that Watney is. We see it through his eyes, from the perspective of someone who not only does it for a living, but really, sincerely loves doing it.

When Watney is thinking things through, talking out loud for his video diary, actually doing the work, you can see that the science of it is his lifeblood. It’s keeping him alive, of course, but his relationship is much deeper than that. As it must be; certainly science keeps astronauts alive on Mars, but going to Mars is something they chose to do, to dedicate their lives for, and the reason they made that decision in the first place is at least in part due to their love of science.

This is said out loud for the audience after yet another setback, when Watney ponders the idea that there’s a good chance he won’t make it back. He leaves a message for his parents, telling them that what he was doing was bigger than just one person and also that he really loved his job.

And I like the fact that he’s a smartass about it too, as shown in this clip of a deleted scene from the movie:

Look, if given the chance, I’d touch the ChemCam too.

I know a lot of scientists like Watney. And I’ll note that this same attitude comes through in all the characters; it took everyone to come together, to work as a team to save Watney. And here’s something I’m not sure many people noticed: There are no bad guys in the movie. The closest we get to that is the NASA director, and even then he’s only making decisions he thinks need to be made. There are no incompetent people, no fools doing something foolish at just the worst moment (example: see any zombie movie ever made) just to move the plot forward. Here, the plot is driven by necessity, and that necessity is “Keep Watney alive against a Universe that doesn’t care whether he’s alive or dead.”

So yeah, I’m very happy with how science was depicted in the movie.

I also really liked the story. I read the book, which is quite good, though very technical and firmly in the category of hard sci-fi. The movie eases up on that somewhat, though it doesn’t flinch from giving details where needed. There’s no way not to make the comparison to the movie Apollo 13, which had a similar premise. What makes both movies gripping is that the stories are well told; we care about the people involved, and that there are failures along the way that need to be overcome.

There were many times I choked up a bit in the movie, mostly when it was showing things I knew to be true: The grueling hard work real people at NASA would in real life put in to save someone, the dedication of the crew, Watney’s can-do attitude.

Also, when he finds Pathfinder (a very real and very important NASA mission to Mars) by following the shroud lines of the parachute, well, that was very, very cool.

Again, I’m a space dork, but my wife, who is not (she’s space dork adjacent), really enjoyed it too. So there’s your calibration mark if you need it.

The Martian
Filmed on location.

Courtesy of 20th Century Fox

And again, I want to stress just how gorgeous this movie is. I saw it in 3-D, which was done quite well. There was one scene in particular when Watney is driving the rover over the Martian surface, and we see him from far above. There are towering, wind-eroded spires of sedimentary rock surrounding the sand-swept valley he’s in, and watching that I had a strong sense of déjà vu: This is exactly what we see from spectacular images taken by orbiting Mars space probes. These are usually shots taken straight down, with vertical perspective squashed, but in the movie we move past them, seeing them for the lofty structures they truly are, and in that moment I felt like I really was moving across the landscape of an alien world.

It was a transformative moment. Ridley Scott directed the movie, so I expect nothing less. He delivers.

Also, in many scenes you can see dust devils whipping around in the background. These are common on Mars, and including them was a magnificent touch.  

Mars dust devil
This is not Hollywood magic: This is an actual image of Mars taken by the Mars Reconnaissance Orbiter in 2012. Click to barsoomenate.

Photo byNASA/JPL/University of Arizona

But the best scene? The very best one? It’s literally the very last shot, in the astronaut training classroom, after Watney gives a speech about space exploration, its dangers and triumphs. When he asks, “Any questions?” and immediately every hand shot into the air.

Oh my. Yes, that’s NASA.

Bottom line: If you’re a space fan, then yeah, see this movie. But then, you probably already have. If not, then go see it anyway. It’s a fun story, crafted well. And if you walk away with a sense of, “Hey, science is pretty cool!” then you know what? We’re good here.

*I’d say this is the best sci-fi movie I’ve ever seen that has Jessica Chastain helping to find astronaut Matt Damon who is lost on another world. Any other movie with that premise would be ridiculous.

Oct. 9 2015 9:30 AM

Pluto’s Sky Is Blue! Well, Kinda.

A new image of Pluto was sent back to Earth from the far, far distant New Horizons space probe, and it’s a doozy: It shows Pluto from the other side, backlit by the Sun. While we’ve seen pictures like that before, this one is in color.

And it looks like Pluto’s sky is blue.


But is it? Well …

The blue ring around Pluto in the picture is due to what’s called scattering. Teeny tiny particles are suspended in the atmosphere of Pluto, and when sunlight passes by them, the red light gets through, but the blue light hits those particles and caroms off in a different direction. The Sun is not directly behind Pluto in this picture—it’s off to the upper right, which is why the ring is brighter in that direction—so the light we see consists of the blue part of the spectrum, scattered around and sent toward the New Horizons camera.

On Earth we see the same thing, and it’s why our sky is blue. In our case, it’s nitrogen molecules in the air (which, after all, is 78 percent nitrogen) that do the scattering. For Pluto, it’s probably from a haze of stuff created when the Sun’s ultraviolet light breaks up simple molecules, which then recombine to make more complex stuff. It’s not yet understood what molecules are creating the blue ring, though.

So, if you stood on Pluto, would you see a blue sky?

Well, no. Not really. It’s not like Pluto has a lot of air. The atmospheric pressure on its surface is only about 0.00001 times that of Earth’s! Even if it were warm and had oxygen, you’d suffocate just as quickly as if you were standing on the surface of the Moon.

But assuming you had a spacesuit with a really good heater, the sky would look pretty black. However, at Plutonian sunrise or sunset, it’s possible that there’s enough atmosphere to see a thin blue line near the Sun on the horizon. I’m not sure your eyes would pick it up but a camera might. Update, Oct. 9, 2015: I've been talking with my pal and New Horizons team member Tod Lauer, who pointed out that although it would be fainter than on Earth, the haze in Pluto's atmosphere should be visible to the human eye around sunset/sunrise, and might very well give the sky a blue cast there. I'm inclined to agree with him; he pointed out that images of a crescent Pluto show the haze is visible above the surface (and even very softly illuminates the surface), and the human eye should be able to pick it up near the horizon. I'm pretty sure the sky would look black above you fading to blue near the horizon, but it's unclear how that transition occurs. That would be a very interesting calculation.

Thinking about this made me curious: How long would sunset last on Pluto? By this I mean, once the bottom edge of the Sun touches the horizon, how long will it take the full disk to disappear?

On Earth that takes about two minutes (neglecting our atmospheric effects, which make it act like a lens and can mess with the timing).

But Pluto is so far away that the Sun’s disk appears to be only about 1/40th as wide as it is from Earth on average (Pluto’s orbit is highly elliptical, so sometimes the Sun will look much bigger or smaller than average, but let’s go with this).* That by itself will make sunsets faster.

Pluto spins much slower than Earth does, once every 6.4 Earth days, so the Sun will move more slowly across the sky than it does here. But that’s not enough to make up for its tiny disk. Once the bottom of the Sun kisses the horizon, it’s all over about 20 seconds later.

So if you can see any blue to the sky, right around the horizon, you’d only have about that long to appreciate it. Update, Oct. 9, 2015: New Horizons PI Alan Stern sent me a note pointing out that while the Sun might only take 20 seconds to physically cross the horizon, due to the scattering in the atmosphere twilight on Pluto before sunrise and after sunset might last for many hours. This ties in with the conversation I had with Lauer above. And another thing: Lauer pointed out that Pluto is tilted so much that it's nearly north-pole-on to the Sun, so if you're on the terminator, the day/night line, the time it takes the Sun to set can be much longer right now! I was just playing with numbers above and hadn't even thought of that. This is clearly more complicated than I had first supposed, though just how complicated still isn't clear! But it shows that no matter how you slice it, sunset on Pluto would be pretty amazing to watch. 

water ice on Pluto
The blue shows the location of potential skating rinks on Pluto. But you might want to take a deep breath ... and pack a really big thermos of hot chocolate. Click to embiggen.


Another interesting image was also released, and it shows the location of water ice on one small part of Pluto’s surface. Pictures alone won’t give that information, but New Horizons has a spectroscope on it, which breaks light up into many individual colors. Different substances have different spectral signatures, so they can be differentiated from one another. That’s how the water ice was mapped.

Interestingly, in this area it’s only seen in those shallow craters near the top, and a few other areas. Very interestingly, all these regions are red. That’s probably due to the presence of tholins, complex organic (carbon-based) compounds that are created in the same way I described above, when sunlight lets molecules rearrange themselves.

Why would water ice be where the tholins are? That’s a good question and the planetary scientists have been asking themselves that same thing. They don’t know. But like everything else in these images, it’s a clue telling us about what Pluto’s doing: what it’s made of, how that material moves around, how it interacts with other material and sunlight, and maybe even hinting at past geological processes.

After all, that smooth region to the right (informally called Sputnik Planum, the left part of the heart-shaped area) doesn’t seem to have any water. It’s thought to be a sheet of nitrogen ice that probably moved glacierlike over the lowlands, stopping where the elevation got higher. At Pluto’s temperature, water ice is harder than solid rock here on Earth, so I wouldn’t necessarily expect it to be there on the plains. It won’t flow! But why is it in the highlands, in spotty areas? No one knows.

Yet. We’re learning more all the time, something new every time a new batch of data is sent back. And even when we get it all, it’ll be years before it’s all analyzed. And also, don’t forget that the spacecraft may fly by a Kuiper Belt object called 2014 MU69 in January 2019—it’s been selected as a new target, but hasn’t been given the official NASA go-ahead yet. But if it is, then we’ll get to do this all over again with a new object.

Well, new to us. It’s actually more than 4 billion years old. What delights await us when we see that up close?

*Correction, Oct. 9, 2015, at 17:00 UTC: I originally misstated that the Sun would look 1/30th as large from Pluto on average than it does from Earth, but it's actually closer to 1/40th. The rest of the math I did is correct. Thanks to my friend and colleague Don Goldsmith for pointing this out to me.

Oct. 8 2015 9:30 AM

When Denial Attacks: Ted Cruz vs. Reality

It’s like GOP presidential hopeful and Texas Sen. Ted Cruz stepped right out of George Orwell’s 1984

On Tuesday he was on a Senate subcommittee hearing about government regulation. Among the people giving testimony was the president of the Sierra Club, Aaron Mair. I’m a fan of the Sierra Club; my wife and I have donated to them many times over the years.


Toward the end of the hearing, Cruz started grilling Mair on one part of his testimony, where Mair said, “That people of color and low-income communities are disproportionately impacted by pollution, and climate disruption should not be up for debate any more so than the science behind climate change itself.”

That, of course, set Cruz off. In a typical denier fashion, he lights into Mair about this, starting off with this:

I’m curious: Is the Sierra Club, is this a frequent practice to declare areas of science not up for debate, not up for consideration of what the evidence and data show?

This is Denial 101, to make it sound like scientists are closed minded. In fact, the exact opposite is true: It is due to the overwhelming evidence and data that scientists are so sure that global warming is real, and caused by human activity. And it’s the people like Ted Cruz—by the way, Cruz got a $15 million check from the fossil fuel magnates Farris and Dan Wilks earlier this year—who have closed their minds to this evidence and data, instead cherry-picking, misinterpreting, or outright dismissing anything that disagrees with their denial.

Watch for yourself, if you can stomach it.

Cruz makes claims so wrong and so long-debunked that I won’t go into detail giving them the evisceration they deserve. Instead, Inigo Montoya–like, I’ll sum up:

Cruz Climate Claim: “The 97 percent consensus paper has been discredited.”

Reality: Nope. As usual when it comes to denial claims, the discrediting has itself been discredited. In fact, the consensus may even be higher than 97 percent, higher even than 99 percent.

Cruz Climate Claim: “Satellite data shows no significant warming over the past 18 years.”

Reality: Nope. Also, nope, nope, nope, and nope. Even the mildest effort can add a lot more “nopes” to that series.

It’s too bad they don’t make senators swear in before they hold hearings.

The thing is, I expect that sort of execrable dumbosity from Cruz. I mean, come on, this is the guy who went on Seth Meyers’ late night talk show and claimed that—and I really wish I were making this up—because it’s cold somewhere, global warming must be wrong.

So I can’t say I’m surprised by Cruz.

head in the sand
Who knew Congressional hearings had such a big sandbox?

Photo by Shutterstock/alphaspirit

No, what’s so upsetting here is how Mair responded. I’m not sure what he was expecting, or how he and his team readied for the hearing, but he was apparently unprepared for the onslaught of misinformation from Cruz, as well as his persistence.

Watching Cruz grill Mair is like watching a septic tank cleaning truck getting into an accident. You know you’re seeing a lot of crap flying everywhere, but you can’t look away.

If Mair had been in an honest conversation with someone he might have done fine, but he was facing someone who long ago chucked reality out the window. With that sort of disadvantage, all Mair could manage to do was repeat himself several times that the Sierra Club sides with the scientists on the issue. But of course this is red meat to Cruz, who clearly is not a fan of science or scientists. He pressed his advantage over and again, and all Mair could do was flail.

Worse, when Cruz asked him to describe the so-called pause, all Mair could say was that it referred to a slowing of global warming in the 1940s. That’s not even right; the 1940s are arguably when the land and ocean temperatures were much warmer than normal for the first time in decades.

I found myself wishing I were there. I know, it’s easy to be an armchair quarterback, but when Cruz said:

And I assume the Sierra Club would issue a public retraction if confronted with the facts that the data are precisely as I described that over the last 18 years there has been no significant warming and indeed that is why global warming alarmists invented the term “the pause” to explain what they called the pause in global warming because the data demonstrate what you just said, that the Earth is cooking and warming, is not back up by the data.

… all I could think was how I wish I Mair had turned it right back around on him, telling Cruz he was grossly wrong; that the data conclusively and obviously show the Earth has been and still is warming, that “the pause” is just a statistical effect, unreal, and that the clear trend is that the Earth is getting hotter.

The huge irony is this: Imagine Mair had asked Cruz if he would issue a public retraction if he were confronted with the facts. The facts that the Earth is still warming up, that oceans are heating up, that sea levels are rising, that the ice caps are melting, that the greenhouse gas CO2 is being dumped into our air to the tune of 40 billion tons every year, and so much more?

Do you really, honestly think Cruz will ever admit that? Or Inhofe? Or Trump, or Carson, or, or, or?

Here is your modern GOP politician, folks. Deny, deny, deny, and when called on it, deny some more and accuse your opponent of what you yourself are doing.

Orwell couldn’t have written Cruz’s words any more concisely.

Tip o' the thermometer to Evlondo Cooper of the Checks and Balances Project.

Oct. 7 2015 12:03 PM

Relive Our One Giant Leap in an Archive of Thousands of Apollo Photographs

If we can put a man on the Moon, why can’t we put 8,400 hi-res scans of the Apollo mission photographs taken by the astronauts themselves on Flickr?

Oh wait. We can. And Kipp Teague did.


Teague is a network and IT director at Lynchburg College, and he and I have two things in common: We’re both University of Virginia alumni (wahoowa!), and we’re both unabashed fans of the Apollo Moon missions. But where I will sometimes write about the missions and talk about how they’re real, he went way, way farther: He rescanned more than 8,000 original photographs taken by the astronauts using their chest-mounted Hasselblad cameras, creating a huge archive on Flickr showcasing the epic journey to the Moon and back.

Included are shots you’ve seen before, and many I bet you haven’t. I’m pretty familiar with the Apollo images, having spent many hours poring over the Apollo Lunar Surface Journal website, studying the images … but even so there are lots of photos I hadn’t seen before, or at least hadn’t noticed.

For example, look at this gorgeous shot of Goclenius, a 70 kilometer wide impact crater near the Moon’s equator:

Goclenius crater
Goclenius crater, criss-crossed by lava flows.

Photo by NASA/Kipp Teague

WOW. This was taken in 1968 by the Apollo 8 crew, which didn’t land, but instead whipped around the Moon to test out the mission trajectory profile before the actual landing the next year. Look at the detail! The gullies cutting right across the crater on the floor are rilles, carved by flowing lava. The floor of the crater is flat, indicating to me that it was flooded with lava, which pooled inside. The rim of the crater shows slumping, too, landslides causing collapse of material for dozens of kilometers around it.

Pictures like that remind me that the Moon may be dead now, but it wasn’t always. It used to be a place of massive, violent geologic events.

Most people will of course be entranced more by the photos of the astronauts themselves. I easily found my favorite Apollo photo of all time: Al Bean standing on the Moon’s surface during Apollo 12, holding a regolith sample container:

Al Bean
A man on the Moon.

Photo by NASA/Kipp Teague

I love the contrast, the glow, of this shot. The streaks on the left are scattered sunlight inside the camera, and you can see the reflection of Pete Conrad, who took this picture, on Bean’s helmet. Note the camera on Bean’s chest; that’s one of the Hasselblads used to take all these incredible photos.

As for why this is my favorite Apollo photo, I described it a few years ago. I had been neck deep in debunking the truly ridiculous claims that the missions were faked and was getting heartburn over it. But going through the lunar photos online I found this one, and something about it—the composition, the artistic qualities of it—caught my eye. And then a realization swept over me, giving me chills and literally raising the hair on the back of my neck:

This is a picture of Al Bean. It's a man in a spacesuit. It's a man in a spacesuit holding a sample container. It's a man in a spacesuit holding a sample container on the Moon. Standing on the Moon. It's a man standing on the freakin' Moon!
Slowly, a wave of awe, joy, and happiness washed over me—a glow of warmth that stays with me to this day. From that moment on I didn't let the conspiracy theorists bug me very much. They were wrong, but even more importantly, they didn't matter. In the long reach of history, they will be forgotten, gnats buzzing around a monumental edifice.

That is the true joy of these photographs. They were taken when we dared to explore beyond the comforts of our home, when we looked skyward and thought, “We can go there.” These photos can inspire the next generation of explorers, those who aren’t afraid to leave safe harbors for worlds beyond.

We did it before. We can do it again.

Oct. 7 2015 9:30 AM

A Lesson in Crewed Language

In many ways, NASA is slow to change. That’s not surprising; it’s a government agency, for one thing, and for another being a tad conservative isn’t such a bad feature when you’re trying to put people into space safely.

But even NASA is ahead of a lot of the curve when it comes to language used when talking about spaceflight. The terms “manned” and “unmanned” have fallen out of favor with the space agency: The NASA History Program Office Style Guide now specifically states that “All references referring to the space program should be non-gender specific.” The only exceptions are for names of buildings and programs; these are—pardon the expression—grandfathered in.*


I think this is great! Words matter. Using more inclusive words is a tacit invitation to people of all flavors, and diversity = strength.

My friend Emily Lakdawalla wrote about this on her blog for the Planetary Society (the comments there are interesting, too, so be sure to check them out as well). The topic came up again when a few science communicators were trying to come up with a good substitute for “manned” and “unmanned.” A lot of us use “crewed,” but as Emily points out (and as I have said many times) it sounds like “crude” when spoken aloud, which can cause momentary confusion for an audience. I’m still not sure what might be best there. “Crewless” works well for “unmanned,” though.

I did a quick search and found that I used the word “crewed” in a post way back in 2007, though it’s unclear if I did that to be more inclusive or just to switch my word usage up a bit. I stopped using the word “manned” a few years ago, though (except when quoting someone, or referring to something like the Manned Maneuvering Unit). I did that when I got into a conversation on this very topic on Twitter with some science communicator friends a while back. I’m a balding, bearded, middle-aged white guy, the very picture of stereotypical science dork. If I figured this out, others can too.

I know a few folks will froth and fume over this change; some people get very hot and bothered when others want to be more inclusive. But things like this cost us very little, and the payoff is large. Even if the cost were higher it wouldn’t matter, because it’s the right thing to do.

Everyone deserves to feel welcome when it comes to math, science, and tech … really everywhere. There’s no way to know from someone’s sex, skin color, or superficial characteristics what they might contribute. We all have brains. What we all need is a chance—and the environment—to participate.

*Space advocate Ariel Waldman points out that this has been in the style guide since 2006!

Oct. 6 2015 12:00 PM

Stephen Ramsden’s Traveling Sun Show

I was puttering around online and happened across something that made me quite happy: CNN put out a short video about my pal Stephen Ramsden. He’s a former air traffic controller who travels around with a very, very impressive array of solar telescopes, teaching kids about the Sun.


I met Steve many years ago and was taken right away with his dedication and enthusiasm for teaching. He’s a natural. That video came out last year, but he’s still out there, going from school to school and showing children sunspots, solar flares, prominences, and more. He’s an inspiration.

Stephen Ramsden
Ramsden setting up for a public Sun viewing in Georgia, his home base state.

Photo by Stephen Ramsden

And not to put too fine a point on it, he takes donations, too (there’s a “donate” button on his Web page). He’s doing a fundraiser right now, and if you donate $100 or more, you’ll get entered to win a Lunt LS80 B1200 solar telescope, and I’ll be honest: I have serious lust for this ‘scope. Happily, I have my own smaller version, so I’m OK. But geez, that’s a sweet machine. And not only that, Ramsden is also raffling off a pair of 8 x 32 Lunt SUNoculars every Friday until Oct. 30 to a donor of any amount.

If you prefer to buy stuff, one of his sponsors, Rainbow Symophony, sells safe solar observing glasses; I have several pair myself and I use them all the time. Stephen doesn't make money from those sales (in fact he gives away glasses for free to anyone who asks if they use them for outreach), but it helps his sponsor so that's agood thing. Come to think of it, I bet such things will be in short supply soon as the Great 2017 Solar Eclipse approaches. You might want to pick up some now. He has other swag, too (again, he doesn't make money for those sales; he does that at cost so others doing outreach can have the same shirts he wears). But donations are best!

He’s doing good work, and I hope he continues to do so for a long, long time.

Correction, Oct. 6, 2015: I originally wrote that the sales of glasses and swag support Stephen, but he sent me a note reflecting the text above.

Oct. 6 2015 9:00 AM

The 20th Anniversary of Exploring Strange, New Worlds

Twenty years ago, on this very date, the field of astronomy underwent a magnificent revolution.

On Oct. 6, 1995, Swiss astronomers Didier Queloz and Michel Mayor announced they had discovered a Jupiter-like planet orbiting a Sun-like star.


This was the very first time a planet was seen orbiting a “normal” star. Planets had previously been discovered around pulsars—the compact and furiously energetic cores of stars that had exploded. But it’s thought that the planets may have formed after the supernova event that created the pulsar, and besides, pulsars are nothing at all like the Sun.

Still, this new planet, called 51 Pegasi b, was a surprise. A big one! While it had about the same mass as Jupiter, it orbited its host star (51 Peg) in just four days, meaning it was on an orbit a mere 8million kilometers from the star. Compare that with Mercury, our solar system’s innermost planet, which never gets closer than about 46 million km from the Sun.

This meant 51 Peg b was hot, cooking away at a temperature of about 1,300° C. No one thought a planet that size could be that close to a star. Did I say the discovery was a surprise? I meant it was a shock, one so profound that it was met with deep skepticism.

As well it should! But its existence was quickly confirmed by team of American astronomers, rivals in the hunt for the first extrasolar planets, as they were once called (we now call them exoplanets).

The planet was found using what’s called the “radial velocity” or reflexive “motion method.” A planet orbits a star due to the star’s gravity. But the planet has gravity, too, so as the planet makes a big circle around the star, the star makes a little circle. In reality both orbit the center of mass of the system, called the barycenter. I describe how this works in my episode of Crash Course Astronomy about the discovery of exoplanets:

As far as we knew at the time, planets like Jupiter had to form far out from their stars, half a billion kilometers or more. Because of this, astronomers who were hunting for exoplanets assumed they would take months or years to make an orbit. They completely missed the presence of 51 Peg b in their data.

Once it became clear these “hot Jupiters” existed, more were found in existing data. Within a few years many more were discovered. It’s now thought they do form far out, but then migrate closer to their star over millions of years. Although they make up only a minority of all exoplanets, these are the easiest to find using reflexive motion; their high mass and close orbit make their signal in the data easiest to see.

Once 51 Peg b was found, the floodgate was opened. HD 209458 b was another hot Jupiter found in 1999, and had an orbit so close to being edge-on that astronomers thought it might actually pass in front of its star, transiting it, dimming its light once per orbit. Careful observations later that same year detected a dip in the star’s brightness (only 1.7 percent!), which gave them the first independent observation of an exoplanet. Any lingering doubts about the existence of these alien worlds evaporated.

The field matured so quickly that NASA launched the Kepler spacecraft in 2009, designed specifically to stare at 150,000 stars to look for transiting exoplanets around Sun-like stars. As of today, Kepler has more than 1,000 confirmed exoplanets under its belt, and well over 3,000 more waiting confirmation.

We’ve seen planets big and small, hot and cold, orbiting small cool stars, huge hot stars, multiple stars, and even in systems with multiple planets.

When I was a kid—heck, when I was in grad school—the only planets we knew of were the ones in our solar system. Using simple statistics, we now think that planets outnumber stars in the galaxy and that most stars may have planets. There may be tens of billions of Earth-size planets in our galaxy alone!

But we had to start somewhere. Exactly two decades ago, 51 Peg b gave us that start.

51 Peg star chart
The star 51 Peg is just off the Great Square of Pegasus, which is in the east after sunset for northern hemisphere observers. EarthSky has a finding chart for Pegasus, then you can use this image to find the star.

Map by Sky Safari

The host star, 51 Peg, is close by, just 50 or so light-years from us. It’s actually very much like our Sun, just a hair more massive, hotter, and bigger. It’s visible to the naked eye, barely, from a dark site. The constellation of Pegasus is high in the night sky for Northern Hemisphere observers right now, in fact. If it’s clear where you are, and you have a pair of binoculars, why not take a look at it tonight?

I will. The exoplanet is completely invisible to even the largest of telescopes, drowned by the light of its oh-so-close star. But who knows: Maybe a photon or two from the planet itself will pass into your eye as you look at the star, absorbed into your retina.

The sky may be brimming with planets. We stand on one among billions. And if you look, a small spark, literally the tiniest reflection of one, could become a part of you.

Oct. 5 2015 11:00 AM

How to Make a Rubber Ducky Comet: Smash Two Comets Together! Carefully.

Why is the comet 67P Churyumov-Gerasimenko shaped like a rubber ducky?*

It was a bit of a surprise when the Rosetta probe, after a decade of travel around the Sun, approached the comet and sent the first decently resolved pictures of it back to Earth. We knew going in that most asteroids and comets just a few kilometers across are oddly shaped; they lack the gravity needed to make themselves spheres, and after 4 billion years of impacts their shape can be decidedly odd.


We even know of a few bowling pin shaped comets, like Hartley 2 and Wild 2. But 67P just reinforced the weirdness of this all with its two lobes mismatched in size and shape.

So, why? What’s going on? Comets are rock, gravel, and dust all mixed together with various ices holding them together, frozen stuff like water, carbon dioxide, and carbon monoxide. Did these weird, dumbbell-shaped comets start off more round and, for some reason, lost more ice in their midsections, leaving behind the two big lobes? Or were they the result of two interplanetary snowballs that collided and stuck together?

New results from the Rosetta team have finally answered this question. 67P used to be two different comets, but they merged to become the bizarre bit of solar system fluff we now know and love.

How? Well, when two comets love each other very much …

Oh wait, no, that’s not it. Well, actually, kinda. Back in May 2015 astronomers came up with a pretty good scenario on how to form a rubber ducky comet. Two smaller comets collide in a slow-speed, grazing impact. Some material is lost, and the two major pieces separate a bit, but the impact was slow enough that they become gravitationally bound. They fall back together, stick, and voilà!

As for the “how do we know?,” that’s more subtle, and quite clever. Rosetta has been orbiting 67P since August of 2014. Over that time it’s taken a vast number of high-resolution images, revealing details of the surface. Both lobes have flat regions all over them arranged like terraces, and the steps in between the terraces show layering; these probably built up layer by layer over time when the comet(s) first formed billions of years ago.

terraces and layers
A close-up of 67P shows flat terraces (colored green here) and layers (red).

Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; M. Massironi et al. (2015)

If the comet formed as a single object that has since eroded, you’d expect the terraces and layers on both lobes to align so that their flat sides were perpendicular to the center of the comet, somewhere in the neck, plated around it (something like the individual panels on a soccer ball, which all are perpendicular to the ball’s center, or, of you prefer, more-or-less parallel to the ball’s surface).

If, instead, the two lobes formed individually and later merged, then the terraces on each lobe would be perpendicular to the center of their respective lobe.

Using 3-D modeling, the scientists mapped the orientation of the terraces. And what they found is the latter: The terraces align to each lobe individually, not to the center of the comet as a whole. This strongly indicates the lobes formed separately, later merging.

comet map
A 3-D model of the terraces in the comet indicate their orientations, showing the two lobes of 67P formed separately, then later merged.

Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; M. Massironi et al. (2015)

That is very, very cool. I’ve been curious about this ever since we literally got the first good pictures of the comet. I allowed myself a bit of speculation back then and felt that a low-speed collision between two small comets was unlikely. I guess I was wrong! While space is big, I neglected to consider that time is also long, and over an eon or four collisions may be likely. After all, 67P isn’t the only object like this; we know of quite a few binary and dogbone-shaped asteroids, too.

How about that? The beauty of this, too, is that the answer gives us insight into more than just why the comet is funny-looking. It also tells us about how comets behave, what their formation processes are like, what happens after they form, and, perhaps most interestingly, how often objects in space collide. That in turn helps us understand the history of our solar system in general, as well as how often the Earth itself gets hit by such cosmic debris.

Over time, we do get hit. The rate of such impacts is a good thing to know, so that we can better understand how to prevent them.

After all, we don’t just want to be a … sitting duck.

*Hint: It’s not because it makes bath time so much fun.