Bad Astronomy
The entire universe in blog form

Nov. 27 2015 9:30 AM

Black Friday… on Mars

Today is the day after American Thanksgiving, considered to be the first shopping day of the Christmas season. Due to the onslaught of eager shoppers to stores, it’s been nicknamed Black Friday.

It’s not restricted to the US, though. The Curiosity rover is having its own Black Friday on Mars — in this case, a bit more literally: It’s reached the edge of the Bagnold Dunes, a windswept region in the vast Gale Crater with huge, towering dunes.


The image above was taken Nov. 25, 2015 (also called Sol 1174 — a “sol” is a day on Mars, which is about a half hour longer than an Earth day, and Curiosity has been on Mars for 1175 sols as I write this). Look at it! You can see the flat, grayish rocks in the foreground, and distant hills in the background, but the view is dominated by lush, gorgeous, rippling dunes (check out this mosaic of images showing a much wider angle, too, because wow).

The dunes are dark, likely due to the sand being basaltic — a dark rock created when lava cools. Over billions of years, the exposed Martian basalt has eroded, creating grains of sand that can be blown around by the wind. But not easily!

Mars has an atmosphere, but the pressure at the surface is less than one percent that of Earth. It has winds, but even though they can move rapidly, the air is so thin they don’t have much force to them. Still, it’s enough to blow around the ever-present Martian dust (made mostly of iron oxide, giving it a pinkish-red color… after all, it’s rust!), and finer grained sand particles.

Dune fields litter the surface, but a lot of them are inactive; the wind there isn’t enough to move the sand around. But some fields are active, and the dunes can be seen to move over time. At Bagnold, the dunes migrate at roughly 0.4 meters per year — a little over a foot annually. That’s not much, but it’s measurable.

Curiosity location
The arrow marks the spot where Curiosity was the day before the dune shot was taken (the most recent map available as I write this). It sits on a "peninsula" of rock between two dune fields, part of the much larger Bagnold field. The image is roughly 500 meters wide, for scale.

Photo by NASA/JPL-Caltech/Univ. of Arizona

These dunes are a juicy target for Curiosity. It’s the first time an active extraterrestrial dune field has ever been examined in situ, for one. For another, examining the material will tell scientists on Earth what minerals are in the sand, of course. Measurements from orbit show that there appear to be some minerals located in some parts of the dune field but not in others. Why?

Also, as wind blows the grains it sorts them naturally by size. The distribution of grain sizes around the dunes will indicate how the winds blow, how the grains deposit onto the ground, and more.

The dune field is pretty big, kilometers across. It’s right on the path of the rover, near the foothills on the northwest flank of Aeolis Mons, aka Mt. Sharp, Curiosity’s eventual goal. It’ll have to cross the dunes to get to the mountain.

I’m personally thrilled by this shot, and I’ve been waiting for this for a long time. I love dunes on Mars! They’re spectacular, and fascinating.

But more than that, they’re so Earth-like in so many ways. The shapes — horseshoe-shaped barchans dunes, or the more stereotypical transverse dunes in the picture above — look achingly like those on our own fair planet.

Mars was once wetter, warmer, and had thicker air. Now it’s all gone. That’s because of eons of pummeling by the solar wind, the flow of subatomic particles from the Sun. The Earth has a magnetic field, protecting us from that, so we’re still warm and wet, even after 4.56 billion years.

If you want to be thankful for something, be thankful for that. And also that in some places, Black Friday is actually and truly a beautiful thing.

Video Advertisement

Nov. 26 2015 9:30 AM

Happy Goatsgiving

There’s a very long list of things I feel thankful for this holiday, far too many to actually itemize. But somewhere on that list, well above the median line, would be these goofy creatures:

We moved out to the country outside of Boulder a little while ago, and there was some extra space in the yard where the previous owners of the house had a small horse barn. We had no use for it, really, and couldn’t decide what to do with it. Then one day we were watching adorable goat videos, and my wife got this look in her eye…


And that’s how I became a goat person. We have two Nigerian Dwarfs and two pygmies. We picked up Clayton Forrester, one of the Nigerians*, when he was still being weaned, so we bottle-fed him goat milk for a week or so. He still likes to sit on our laps and cuddle while he chews his cud. It’s ridiculously cute:

Seriously. C’mon. There's also this

I post pictures and videos of these dorks all the time on Instagram; follow me there if you want to see them. And you do.

I love these silly animals, and I love to share their antics with people online. It may not save the world, but you know what? Every little bit of joy we share, no matter how small, incrementally makes the world a better place. If a million people do that, even once or twice a week, it would add up.

Happy Thanksgiving, folks. Make the world better, even just a little.

* The other goats are Jack, Batman, and Sam. Someone asked me if Jack and Sam were from Stargate SG-1, and I could've kicked myself for never seeing that. But no, Jack is actually Jack Burton, from the single greatest movie ever made. I like to think that Clayton is named after a character in another favorite movie, but my daughter named him, so it's probably for this guy.

Nov. 25 2015 9:30 AM

On the Anniversary of Two Scientific Revolutions

This week marks the (very round number) anniversaries of two of the most important scientific papers ever published.

One you’ve heard of—or at least, you’ve heard of the author and its concepts. The other you probably haven’t. Yet it is equally as important, and tells as great a tale.


First things first: On Nov. 25, 1915—100 years ago Wednesday—Albert Einstein submitted a paper to the Proceedings of the Prussian Academy of Sciences in Berlin titled, “Die Feldgleichungen der Gravitation,” or “The Field Equations of Gravitation.”

If that doesn’t sound familiar, maybe it would help if I said that this paper laid the groundwork for Einstein’s General Theory of Relativity.

Oh, right. That paper.

Einstein published his Special Theory of Relativity in 1905. That groundbreaking work showed that space and time were relative, and that if you moved near the speed of light relative to another observer you’d see these two properties very differently. Since then, the Special Theory has since been experimentally verified countless times.

After publishing it, Einstein started working out how to add gravity to this mix. That’s extraordinarily difficult, and the math fiercely complicated. It took him many years, but he submitted the paper in November 1915, and it was published in the next month. In it, he made a startling and fundamental claim: Gravity is not really a force as had been thought, but instead is a warping of space caused by matter.

Sound esoteric? Well, that’s because it is, a bit. Centuries earlier, Isaac Newton had proposed his theory of universal gravitation, describing gravity as a force, attracting one object to another. It depended on their mutual masses and distance from each other. Newton’s idea works pretty well, and in fact we still use it today to plot courses for spaceships!

The term “force” is difficult to accurately define in layman’s terms,* but you can think of it as some sort of connection between objects, attracting them or repelling them. That’s how Newtonian mechanics works out.

But Einstein’s General Theory changed all that. He found that gravity is not a force between two objects, but a property of space itself, a geometric bending or warping of it. It’s usually described this way: Matter tells space how to bend, and space tells matter how to move.

A smiling lens
This smiling galaxy cluster is actually the product of gravitational lensing: the warping of spacetime by a foreground clump of galaxies distorting the path of the light coming at us from a background clump of galaxies. Click to informenate.

Photo by NASA and ESA

It was a fundamental shift in how we thought of space and matter, and fit right in with Einstein’s previous Special Theory work in showing that space and time were connected. Their implications are wide-ranging as well; for example, the solutions to these General Theory field equations describe the structure of space, and naturally predict the existence of black holes. They also predict the existence of gravitational lensing (which we’ve seen, and which led to a confirmation of the existence of dark matter), gravitational radiation (which we’ve detected indirectly), and gravitational time dilation (which we’ve also seen).

An even more profound impact of these equations is that they lead the way to understanding how the Universe itself formed and evolves, and even of its ultimate fate.

Heck, without the General Theory your map app wouldn’t work!

So, yeah. It’s kind of a big deal.

The second anniversary we’re celebrating now is no less in stature, and has an equally deep practical impact on the world.

One hundred fifty years ago, in late November 1865, James Clerk Maxwell published his paper called “A Dynamical Theory of the Electromagnetic Field,” and in it he wrote down a set of equations we now call Maxwell’s equations, which should hint at their importance. Why? They describe how electricity and magnetism are two sides of the same coin, actually the effects of a single force called electromagnetism. Up to that point they were treated separately. Maxwell united them.

The importance of this can’t be overstated! His equations show that electricity can be used to induce magnetism, and vice-versa. We generate electrical power based on this. He showed that light is itself a wave, traveling through space as an oscillating electromagnetic field. Ever heard of the electromagnetic spectrum? Yeah. That’s from Maxwell. His equations show how light behaves, and in fact you can derive the speed of light from these equations if you can measure some other fundamental properties of space.

The spectrum of the Sun; thanks to Maxwell we understand how light behaves as a wave, which led to fundamental breakthroughs in astronomy and physics.

Photo by N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF

It is no exaggeration to say that Maxwell’s equations are at the very foundation of our modern civilization: computers, electrical systems, global communication—all of this comes straight out of these equations. Einstein’s ideas about relativity derive from them as well.

But there’s more to this story. Maxwell wasn’t a university scientist, working under a research grant to investigate the disparate fields of electricity and magnetism. Nor did he set out to revolutionize the entire planet’s civilization. He was just a curious person, someone who delighted in nature, who was puzzled by how it works, and who wanted to understand it.

And this led to the economic basis of a world.

This story is lovely and wonderful, and was best told by Carl Sagan in his opus, The Demon Haunted World: Science as a Candle in the Dark. I strongly urge you to buy and read that book; it’s magnificent, and many (including me) consider it Sagan’s best work. In one chapter, he talks about Maxwell and his equations, and it’s a paean to allowing scientists to study the Universe unfettered by politics (academic or governmental), allowing their imaginations to guide them.

In many fields of science there must be moral and ethical guidance, of course, but in theoretical physics it is the math and physics themselves that are the guide. Maxwell followed them and revolutionized a world. Einstein followed them and revolutionized our thinking about the Universe.

And today we celebrate the anniversary of both.

For science!

Although, in this case, one could quote Kenobi et al., 1977: “[A force] surrounds us and penetrates us; it binds the galaxy together.” While widely admired and quoted, many find Kenobi’s dabbling in mysticism a bit off-putting.

 To be fair, scientists before Maxwell knew that electricity and magnetism influenced each other, but Maxwell quantified it, defined it, and it’s from there that our modern power systems are derived.

Nov. 24 2015 12:21 PM

Blue Origin Milestone: Rocket Lands Safely After Trip to Space

Jeff Bezos’ rocket company Blue Origin just surprised everyone by revealing its New Shepard* rocket reached an incredible milestone on Monday: In a test run, the rocket took off vertically, reached space, then landed again vertically minutes later.

The rocket launched from their site in west Texas, accelerating to a top speed of about 4,600 kph, and achieving an altitude of more than 100 kilometers, the technical height defined to be the start of space (called the Kármán line). They also deployed the crew capsule at a height of about 6 km above ground, which parachuted safely back to Earth.


Blue Origin put together a nice—if somewhat misleading—video of the event. I say that because in the middle of the real footage they inserted CGI animation of a crew inside the rocket’s capsule; this was an uncrewed flight. Still, the video is cool:

I like the shots of the landing from various angles at the video’s end; it looks more like a Hollywood sci-fi movie than reality! But real it is. The descent is unnerving; the rocket engines don’t reignite until it’s only about 1,600 meters above the ground, and it decelerates pretty hard. That saves a lot of fuel and makes perfect sense, but it’s a little scary to see it! Still, the rocket performed extremely well, and landed only a little over a meter from the center of the launch pad. Amazing.

Blue Origin attempted a similar test flight in April, but the landing system hydraulics failed and the booster crashed. Apparently, and happily, this issue has been addressed.

So congratulations to Jeff Bezos and his team on this incredible test! This is very exciting to see.

New Shepherd
A different angle on the landing. The Sun and tilted horizon are on the left.

Photo by Blue Origin, from the video

However, I’m seeing some confused coverage of this event, and I want to clear a couple of things up.

First, yes, this launch is a big deal! It shows that Blue Origin is making excellent strides towards commercial space launches, a field currently dominated by SpaceX. Getting up to the Kármán line is a major achievement at all, let alone successfully deploying the capsule and then landing the rocket again. SpaceX itself is based on the idea of competing against big government contractors, so competition for them is good.

Bezos himself took to Twitter to announce the success, and made a subtle dig at Elon Musk and SpaceX at the same time:

I smiled, but I have to point out that, as great a technical achievement as this was, what Bezos has accomplished here is quite different than what Musk has been attempting.

The Blue Origin New Shepard is a suborbital rocket, designed to go straight up into space and back down again. The SpaceX Falcon 9 is an orbital rocket, which takes vastly more energy (in other words, much higher speed) to achieve its goal.

Musk responded on Twitter pointing this out:

He’s right. Landing a booster from an orbital flight is hugely harder than from a suborbital one. For orbital flights, the booster not only has to move far faster, it also will have a large horizontal speed relative to the ground to get to orbit, so slowing it is more difficult as well. SpaceX has not yet achieved a successful landing this way, but what they’re doing is literally an order of magnitude more difficult than what Blue Origin did.

Then, in my opinion, Musk made something of an unfair comparison himself. He tweeted:

True, but Grasshopper (a test vehicle designed to launch and land vertically) only got 744 meters above the ground, wasn’t designed for high-altitude flights (it’s a testbed for the F9 landing tech), and didn’t deploy a capsule. The later F9R tests based on Grasshopper were very successful as well, but only got a kilometer off the ground. What Bezos did yesterday was far more technically difficult.

Update, Nov 24, 2015, at 18:00 UTC: Musk has continued to tweet about this, correctly pointing out that suborbital flight and landing has been done before by SpaceShipOne and arguably the X-15 rocketplane. Musk also noted the series of water landing attempts using the F9 booster.

Mind you, suborbital flights are important. It’s more than just a tourist attraction (though a pricy one); real science can be done on such flights, even though weightlessness only lasts a few minutes. Blue Origin looks to be getting quite close to having the ability for these kinds of launches.

The company is known for secrecy, tending to announce achievements only after they’ve been reached. That’s understandable, and it can work to Blue Origin’s advantage in the media as a tortoise-and-hare story (one I think Bezos is happy with). That means details about their future goals are unclear, but the goal itself is obvious: getting in on the lucrative orbital satellite market as well. As I pointed out, the physics of this is quite different, and it’s a long journey there … but they just took a solid step in the right direction. Up. And back down again.

Correction, Nov. 24, 2015: I originally misspelled the rocket as New Shepherd; but it's punningly named after Alan Shepard, the first American in space.

Nov. 24 2015 9:15 AM

Just Another Day on Pluto

Pluto is an odd little beast.

You knew this, if you’ve been paying attention at all these past few months. But one thing that struck me recently is its 6.4-day rotation rate. That’s weird; most free bodies in the solar system spin either much faster than Earth or much slower. Jupiter, Saturn, Uranus, and Neptune have days that are shorter than Earth’s, ranging from 10 to 17 or so hours. But Mercury takes 60 days, Venus a whopping 243 days. Mars spins at almost the same rate as Earth, with a day 24 hours 37 minutes long.


So Pluto’s weeklong spin is an oddity. If you could watch it, what would it look like?

Well, it would look like the photo at the top of this post. Those images were taken by the New Horizons probe as it passed Pluto in July. As the spacecraft approached, it took a lot of snapshots of the little world, and over time was able to see it at various points in its day. These were collected, scaled to the same size, and arrayed to show a day in the life of the frozen ice ball.

Each shot shows the highest-resolution image taken for that particular point in the day. The shot at the 3 o’clock position was taken from farthest away (about 8 million kilometers), and the one at the 6 o’clock position was the hemisphere seen by the probe when it passed a mere 12,500 km over the surface.

You can see the familiar heart-shaped Tombaugh Regio, a flatter region that is covered in nitrogen ice (the left lobe, Sputnik Planum, is much smoother than the right lobe). I like how you can see different resolutions blurring the features at different times; it is physically showing you what can and cannot be seen clearly during various points in the flyby.

Charon, Pluto’s outsized biggest moon, orbits the world in that same 6.4-day period, and also spins at the same rate (this is not a coincidence). The New Horizons team also put together a similar mosaic for Charon:

The full face of Charon.

Photo by NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

I’ll be honest: Despite the somewhat lower contrast and details, I like this one better. I think it’s because the north pole of Charon is so clearly marked by the dark spot nicknamed Mordor Macula. It’s not clear why Mordor is dark (and red), but it may have to do with organic molecules from Pluto raining down on it.

Geez. Pluto and Charon are weird.

Which brings me back to the length of the day/month there. Charon and the littler moons may have formed by a huge impact; a big chunk of ice and rock smacked Pluto hard long ago, and the debris coalesced to form those moons. The impact could have changed Pluto’s rotation rate, and then tidal interactions with the newly born Charon would have modified it as well. Once everything locked into place, we got this weeklong spin of the three systems (Pluto itself, Charon itself, and the two together orbiting each other).

Most small objects in the solar system have had their spin rate modified. Earth spun much faster before our own Moon formed in much the same way as Charon. Venus spins slowly and backward, so it may have been flipped over by an impact (or some other process we haven’t quite figured out). Mercury’s proximity to the Sun played havoc with its spin. Asteroids spin up due to sunlight.

So perhaps Pluto isn’t all that odd after all. It’s actually quite normal in its weirdness … or, at least, that’s my spin on it.

Nov. 23 2015 9:30 AM

Rep. Lamar Smith Continues His Harassment of Scientists

The saga of The Man in Congress in Charge of Science but Who Doesn’t Understand It continues.

For those new to this, Rep. Lamar Smith, R-Texas—chairman of the House Science, Space, and Technology Committee—doesn’t think global warming is real. He thinks it’s a huge conspiracy by climate scientists who fudge the data to make it look like the planet is heating up, because Obama.


I wish I were being hyperbolic. But this is literally true.

In Part 1 of our tale, Smith subpoenaed Kathryn Sullivan, the administrator of the National Oceanic and Atmospheric Administration, claiming that scientists in her agency were “altering the data.” Smith got this idea after a paper was published in Science showing that the global warming “pause” so lauded by climate change deniers didn’t, in fact, exist. This research was done by a team of NOAA scientists and, I’ll note, is correct. The “pause” isn’t real.

That didn’t stop Smith. He also demanded the data, methodology, and emails of NOAA scientists be released (despite the first two already being publicly available). We also learned that Rep. Eddie Bernice Johnson, D-Texas—who is the senior Democrat on the committee—sent Smith a letter accusing him of harassing and second-guessing scientists, and also pointed out he’s not qualified to assess the data or methods. This, too, is correct.

In Part 2, Smith made public his conspiracy theories about scientists fiddling with the data (they did this, Smith claims, “to advance this administration’s extreme climate change agenda”, in case you were wondering just how far removed from reality Smith is on this), and I showed why these ideas are nonsense (to be very very very very polite). In Part 3 I went into more detail, showing that Smith doesn't understand even the most basic principles of scientific data measurement.

And now here we are, at Part 4 of a presumably infinite series. His new claim? That the NOAA Science paper in question was rushed into publication, and that Smith has “whistleblowers” who will attest to it.

However, that’s at odds with the facts. Rep. Johnson wrote yet another letter to Smith, outlining where his claims are clearly wrong. She lays out a timeline, showing that the paper was submitted to the journal in late 2014, and took months to publish. Not only that, it relied on data from papers submitted to the journal in 2013—hardly a rush job.

I’ll note that these alleged whistleblowers had ample opportunity to file a complaint with NOAA itself. Yet no complaints have been registered (even though NOAA has an obvious and easy-to-find scientific integrity policy). 

Update, Nov. 23, 2015: A Washington Post article makes the case that not only was this paper not rushed, it actually underwent more scrutiny than usual.

On top of all this, Smith has sent several letters to NOAA and other groups—seven in total—with his demands, but only just now, in his most recent one, did he mention whistleblowers. That’s curious; Johnson has asked him repeatedly why he thinks the scientists have fiddled with the data, but he’s been silent on that.

It’s also curious, as Johnson notes, that Smith has declined to share any of the information about his alleged whistleblowers with any of the Democratic minority on the committee. If he’s not purely politically motivated, why wouldn’t he give this information to them? Who are these whistleblowers? What are their specific claims? Why has Smith waited so long to mention them?

I strongly urge you to read Johnson’s letter; it really shows that Smith’s actions are the results of political grandstanding. NOAA had been complying with his requests, as silly and wasteful as those requests were, but Smith ignored this and kept making more and more unreasonable demands. Finally, NOAA put its foot down; NOAA Administrator Sullivan has refused to comply any further.

I’ve been saying that Smith is harassing scientists, and he’s abusing his power of congressional subpoena. Now we have even more evidence: He’s been pressuring Commerce Secretary Penny Pritzker over all this, trying to get her to in turn pressure NOAA to turn over the scientists’ emails.* If NOAA doesn’t comply, he’s threatened to subpoena the secretary herself.

Not only that, but his threats of Sullivan are atrocious. As Johnson points out, in what may be my favorite part of her letter:

I think it might be informative to take note of whom you are threatening. Dr. Kathryn Sullivan is PhD [sic] geologist, former naval reserve officer, former three-time NASA astronaut, former chief scientist of NOAA, and former member of the National Science Board. As an astronaut, Dr. Sullivan became the first American woman to ever “walk” in space. Dr. Sullivan is the very definition of service to country, and she is a role model for us all. I highly doubt Dr. Sullivan is intimidated by your threats, but it is an indication of how low the Majority is willing to stoop to perpetuate their anti-science agenda when a legitimate American icon is dragged through the mud in furtherance of an ideological crusade.


Smith is out of control. I earlier likened him to Sen. Joseph McCarthy, who, in the 1950s, went on a huge and reckless witch hunt, looking for Communists in government, ruining people’s careers and lives in the process. That likeness grows ever clearer into focus.

I don’t see any reason to change my assessment of Smith now. He is a demagogue, using and abusing his power to stifle scientific research, to create a climate of fear and pressure for those scientists, and to obfuscate and further cast doubt in the public’s mind about the reality of climate change and its effects (an effort that has of course found purchase with the usual right-wing media suspects).

This behavior is as appalling as it is damaging and clearly based on falsehoods. The world is warming up. We are seeing the effects of that now. And we know that it’s because of the damage humans are doing, pumping billions of tons of carbon dioxide into the air every year. These are facts.

But the majority of Republican senators and Congress members in charge of critical committees reject these facts, replacing them with their own fantasies of conspiratorial scientists. These people are putting our nation’s security at risk. It’s good news that some of the GOP in Congress are willing to be swayed by facts, but the sad and embarrassing truth is the ones in key positions are not. And while they fiddle, the world burns.

*Correction, Nov. 23, 2015: This post originally misspelled Penny Pritzker’s last name.

Nov. 22 2015 9:30 AM

The Milky Way, in 46 Billion Pixels

Well, this is cool: Astronomers at the Ruhr-Universität Bochum in Germany have created a ridiculously huge 46 billion pixel map of the sky! According to the press release, it’s the largest astronomical picture ever created in terms of pixel size (I have not heard of any larger, for what it’s worth).

Even better? It’s interactive. You can pan around, zoom in and out, and fiddle with the colors, too.


Here’s the link to the map. But, a couple of caveats. It’s not lightning-fast; I had to wait many times for it to load (I checked; my download speeds are around 20 Mbps). Also, without instructions it’s a little tricky to use, but if you play with it for a while you’ll get the hang of it. You can also type the name of an object into the finder box on the lower left; try “M 20” (the Trifid Nebula, screenshot shown below), “eta car” (for the bright star embedded in the Carina Nebula), or “M 16” (the Eagle Nebula, shown at the top of this post). By the way, nebulae appear green due to the filters they used to make the map.

The map isn’t of the whole sky; it’s actually a series of fields located along the plane of our Milky Way galaxy. Still, the numbers are impressive:

  • Total number of fields making up the mosaic: 268
  • Area of sky covered: 6° x 220° for a total of 1,323 square degrees (that’s more than 6,500 times the area of the full Moon on the sky!)
  • Total file size: 194 Gigabytes
  • Total number of stars: About 16 million
  • Number of variable sources: 64,151

That last one was part of the reason why they did the survey. Here’s the scoop: The observations were made with a pair of small, 15 cm (6 inch) robotic telescopes located in Chile. Each ‘scope has a very wide 2.7° field of view, and they observe each of the 268 fields roughly once per month. They can detect stars down to about 18th magnitude, which is pretty faint: The dimmest star you can see with your naked eye is about 60,000 times brighter!

Many surveys go fainter, but then bright stars tend to blow those observations out. This survey was done specifically to reach middle brightness stars at high enough resolution to distinguish tightly spaced objects well.

The Trifid Nebula, a combination of glowing gas and dark dust that appears to split the nebula in three sections, giving it its name.

Photo by Haas et al.

By spreading out the observations over time, they can detect objects that change brightness. Some stars are variable, getting brighter and dimmer with time. Others are in binaries where one star blocks the other every orbit (called eclipsing binaries). Stars explode, asteroids fly by, and so on.

Analyzing this new dataset for his Ph.D. work, Moritz Hackstein found a total of 64,151 stars that changed their brightness, and nearly 57,000 of them were previously unknown! That’s pretty astonishing.

Surveys like this are precious and valuable. If an object changes catastrophically, we only get one chance to observe that event. This survey keeps a record of everything that happened in that section of the sky for nearly five years.

It’s also just fun to play with. I enjoyed scanning along its length, trying to see how many objects like nebulae I could identify. Only one big one stumped me (the Running Chicken Nebula, yes, seriously), but a couple of bright stars got past me, like Alpha Centauri.

It also gives you a sense of just how flippin’ huge the sky is. Zoom in, zoom out, pan around, but bear in mind: The total sky is about 40,000 square degrees. This map is therefore only about 3 percent of it.

There’s still a lot more to see.

Nov. 21 2015 9:30 AM

Black Holes Make Me Drool

Nobody’s perfect. Some people come closer than others, but that’s usually because of good editing. In my case, I have proof: Here’s the fourth Crash Course Astronomy blooper reel, showing that we don’t just bang these episodes out. We have to edit them a lot.

Ironically, even these outtakes are edited; not all of them are funny. My editor Nicole Sweeney, only picks the ones that a) make her laugh, and 2) make me look like a dork. Her job is way too easy.


Can’t get enough of this sort of thing? Then watch the first, second, and third blooper reels, too. And all the currently aired episodes of Crash Course Astronomy are available in one easy-to-binge list. Ten straight hours of astronomy!

Nov. 20 2015 9:30 AM

Great Photo of a Twisty Rainbow Cloud—Iridescent Pileus

Regular readers know how much I love a) clouds, and 2) optical phenomena in the sky, so I can say with complete honesty that this is by far the coolest pileus cloud with iridescence you’ll see all day.

OK, what?


Right. You’ll probably want some details.

This photo was taken by Beckie Bone Dunning on Oct. 29, 2015, when she was in Jamaica. There were storm clouds approaching, almost covering the Sun, when she snapped this shot. Being the huge dork that I am, I knew right away what was here.

First, the colors are from iridescence, a complicated physical phenomenon. I’ve written about this before:

Iridescence is a weird phenomenon. You need lots of tiny raindrops (or ice crystals) all the same size over a large portion of the cloud. In a rainbow, the lights goes into the droplets and gets bent (twice) to create colors. In iridescence, though, the light actually bends (diffracts) around the droplets. Different colors bend by different amounts, splitting the colors apart. The size of the raindrop needs to be roughly the same size as the wavelength of light, so when I say “tiny” I mean it: The drops must be less around a micron in size! A human hair, by the way, is about 100 microns in width, so these really are teensy drops.
But it’s more complicated than just that. The cloud also has to be what’s called optically thin; that is, mostly transparent so that on average a beam of light only hits one droplet and only gets bent once. If it hits multiple drops the colors get washed out. That’s why this happens more often near the edges of clouds, where they’re thinner. On top of that, the light waves interfere with each other, similar to how waves in a bathtub add together or subtract from each others’ wave heights as you wiggle around (and please, don’t deny you’ve ever done this playing in the tub; it’s fun, and educational!). These processes combine in complicated ways to produce these different colors.

Note that the colors in iridescence are different than the ones in rainbows because they're generated in a different way; you can get teal, pink, and more from iridescence.

So that explains the colors. What about the weird, twisty shape?

Ah, that’s because this isn’t just a cloud, it’s a pileus cloud. These are thin, cap-shaped sheets of cloud that form above rapidly rising columns of air. For example, in a cumulonimbus cloud, the shaft you see is due to the warm air rising, which usually bubbles into that cauliflower-shape head at the top. If there is a humid layer of air above it, the rising air will push it up (like a fist pushing through a rubber sheet), where it expands and cools. If it cools below the dew point, droplets form, and you get a pileus cloud.

Pileus clouds are thin and have tiny water droplets in them. Perfect to make iridescence! You have to be at the right spot to see them, when the clouds are near the Sun … which is exactly where Dunning was. Voilà.

Amazing. I’d LOVE to see something like this. I’ve seen both pileus and iridescence before, but never at the same time. I’d expect it’s rare where I live; we tend to get cumulonimbus clouds forming to our east, as air rises over the Rockies and picks up moisture as it crosses the plains. That happens in the afternoon, when the Sun is to the west, so they happen in opposite spots in the sky. Ah well.

But that arrangement does supply us with a lot of rainbows, so I can be pretty happy with that, too.

More cool weather stuff:

Tip o’ the nebular hat to Jacob Black.

Nov. 19 2015 9:30 AM

The Glory of Spirals

Because why not, here are two glorious spiral galaxies to brighten your week.

The first image is by my friend Adam Block, and it shows NGC 488, a tightly wound spiral about 100 million light-years away. I love how delicate it looks; the blue arms are well-separated but fluffy; I’d almost call this a flocculent spiral.


The inner region is very interesting; it’s much redder, which generally indicates the presence of older stars—blue stars are very massive and don’t live long, exploding as supernovae after only a few million years or so. That leaves longer-lived redder stars behind, so where you see big red regions you’re usually seeing a place where stars haven’t been born in a long time.

It’s interesting that you can still see a spiral pattern in the red inner region and a clear set of dust lanes as well. Thick dust is dark, blocking light behind it. Thinner dust, though, can scatter away blue light (like the Earth’s air does to sunlight, making the sky blue). I wonder if there’s just a lot of dust spread around that inner region of the galaxy, reddening it. A quick literature search didn’t turn up anything, though.

Either way, I strongly urge you to check out Adam’s larger and higher-resolution image of this object. It’s stunning, with bright stars and scattered background galaxies, with some of the latter many hundreds of millions or even over a billion light-years away. It’s gorgeous.

Speaking of gorgeous, the second image is of M 94, a much closer spiral at about 16 million light-years distant. Hubble observed it, showing just the inner region, producing this spectacular image:

Starburst galaxy Messier 94
M 94 via Hubble shows amazing detail in the spiral arms.

Photo by ESA/Hubble & NASA

That ring of blue stars is real; M 94 seems to be producing a lot of young stars in a circular region around the nucleus. The size of the ring indicates it may be due to a resonance phenomenon, forcing gas clouds and stars orbiting the galaxy at that distance closer together. It’s a bit like pumping your legs in time with swinging on a swing, forcing your arc to go higher; in this case it has to do with the gravity of the rotating galaxy as a whole “pumping” the orbits of objects within it. Anyway, it causes gas clouds to collide, collapse, and form stars.

That becomes a little more obvious in another shot of M94 from Hubble … well, actually the same shot, but this time including colors that highlight the presence of those gas clouds:

M 94
M 94 gets a little more surreal when the pink glow from hydrogen gas is added.

Photo by Robert Gendler, NASA/ESA, Subaru

Astrophotographer Robert Gendler put this shot together, and he included some data from the Subaru Telescope as well. The pinkish-red is emitted by the gas clouds, and the blue color of the young, massive, and very hot stars is a lot more obvious.

Man, I do so love splashy spiral galaxies. The science and physics involved in their structure is both powerful and sublime, and their beauty … well, that’s tough to match.

Want to learn more about spiral galaxies? Then do I have a Crash Course Astronomy episode for you!