Bad Astronomy
The entire universe in blog form

April 24 2016 9:30 AM

A Twice-Lit Moon Kisses the Horizon

Sometimes you see a photograph that’s just so wonderful you can’t wait to show it to other people.

It was taken by Petr Horálek, a European Southern Observatory Ambassador—the ambassadors are a group of excellent photographers who shoot pictures of the ESO observatories for public outreach.

The photo was taken on April 6, just minutes before sunrise. Smack dab in the center is Venus, cruel twin of the Earth, covered in clouds so reflective they make the planet the third brightest natural object in our skies.

Below it is the crescent Moon, less than a day before its new phase. The crescent is so thin it’s almost an afterthought. Amazingly, the rest of the Moon’s surface was unlit by the Sun. So why can we see it? Earthshine! Light from the Sun hits the Earth, reflects off of it, illuminating the Moon, which then reflects it back into space, and to Earth. Our planet is very bright in the lunar skies, 50 times brighter than a full Moon. That’s enough to softly bathe the surface of our satellite in light.

Note too the Moon looks a little squished. That’s an effect of our atmosphere, which curves along with the Earth’s surface. Near the horizon, the light from the bottom of the Moon goes through a thicker layer of air than the top part of the Moon. The air acts like a lens, bending that light, making the Moon look flat.

Horálek timed this photo perfectly, getting the shot just as the Moon cleared the distant mountains. Had he waited much longer the Sun would have lit things up too much anyway. This was a time exposure, too: You can see the faint stars of Pisces surrounding the Moon and Venus.

And let’s not ignore the foreground! The silhouetted dome houses the 1.2 meter VLT Auxiliary Telescope, part of the Very Large Telescope array. See the two people crouched nearby? That’s my friend Babak Tafreshi on the left and Yuri Beletsky on the right, wrapping things up after a long night of photography in the incredibly rich and dark skies of this remote location in the high desert of Chile. I’ve featured both their works on this blog many times; click their names to fill your eyes and brain with delight.

I dream of capturing a photograph like this some day. But I just dabble in this; Horálek, Babak, and Beletsky are professionals. I might feel a pang of jealousy seeing shots like this, but it evaporates rapidly as I take in the sheer beauty. I’m glad there are so many people out their willing to collect the few photons the Universe graces us with, and share them with the world.

April 23 2016 9:30 AM

Valley of the Cosmos

Photographer Michael Shainblum is a wonder. His photographs are just stunning, one after another. I’ve been following his work for years, and every time he posts something it’s awe-inspiring.

Oh, you want an example? Then how about this for your eyeballs?

April 22 2016 9:15 AM

Noon on a Comet

A couple of weeks ago I posted a dramatic shot of the comet 67P/Churyumov-Gerasimenko backlit by the Sun, taken by the Rosetta spacecraft from a distance of a few hundred kilometers. I mentioned how the spacecraft was on a long looping path that would soon take it back to the comet, passing directly between it and the Sun at a distance of about 30 kilometers, which should make for some very pretty pictures.

Well, here you go: As promised, the image above shows that exact event! Rosetta was 29.9 kilometers above the surface of 67P when it took that shot on April 12, using the OSIRIS wide-angle camera. As you can see, shadows are nearly non-existent, and only appear where there’s a sudden change in the topography of the comet (cliffs, shelves, and the like) near the edge of the comet.

And that glowing spot left of center is real, too! There are lots of fancy names for it, including the zero phase effect and heiligenschein, but I think my favorite is “opposition surge.” Poetic and scientific, all at the same time.

There are two reasons for it. One is that from the spacecraft’s view, the Sun is directly behind it, so the Sun’s light is shining straight down on the comet. At that spot directly below the spacecraft you don’t see shadows, so the surface looks brighter. Not only that, but some types of terrain bounce sunlight straight back in the direction it came. If you’re on that line, you see that spot on the ground being brighter than the area around it.

The Sun is in the opposite side of the sky as that spot, hence the term “opposition,” and the surge is pretty obvious. Heiligenschein means “halo” in German, and if you’ve ever seen a faint glow around the shadow of your head as walk past a patch of dewy grass, you’ll understand that term, too.

As for zero phase, the technical term for the angle between the source of light, the observer, and the spot illuminated is the “phase angle.” When they’re all on a line that’s defined as zero. The term should actually be familiar to you in another guise: The angle between the Sun, you, and the Moon defines the Moon’s phase! Surprise! You know more technical stuff than you probably thought.

By the way, the Rosetta shot is looking up at the flattish “underside” of the comet, the broad region across the wider of the two lobes making up 67P’s rubber ducky shape. You can see part of the smaller lobe, the “head” on the left. The shape looks funny when shadows go away; it’s hard to tell what’s what. Shadows actually help us understand the terrain, and can be used to make 3-D maps of the surface. But this zero phase angle helps too; the surge can be used to understand better the surface on much smaller scales; different sized grains of ice or other materials change the brightness of the surge.

Fantastic! Science and geometry come together to form beauty. As they often do.

April 21 2016 11:45 AM

A Seriously MASSIVE Bubble Blown in Space Celebrates Hubble’s 26th Anniversary

On April 24, 1990, the Hubble Space Telescope was lofted into orbit on board the Space ShuttleDiscovery. Sunday is the 26th anniversary of this grand event, and to celebrate, the good folks at the Space Telescope Science Institute have created a new and simply spectacular image.

Get a load of this!

That is the Bubble Nebula, aka NGC 7635. It looks almost delicate, doesn’t it? Like a thin soap bubble floating in space.

But that's a lie. Nothing about this tremendous beast is delicate.

April 21 2016 9:00 AM

Look! Up in the Sky! It’s a Bird, It’s a Plane … Actually, It’s a Bird and a Rocket.

If you look up into the sky long enough, you’ll see the weirdest things.

Astrophotographer Grahame Kelaher was in Western Australia late at night on Feb. 6, and he saw the odd, fan-shaped blue glow in the photo above moving across the sky. He wasn’t surprised, though: He planned for it!

That’s not some nebula—it’s actually the glow from fuel dumped into space by the Centaur upper stage of a United Launch Alliance Atlas V rocket! The Atlas launched from Florida on Feb. 5,* carrying an Air Force Global Positioning System satellite GPS IIF into orbit.

The Atlas was configured for this launch as a two-stage vehicle. The lower, first stage, lobbed the upper stage, called a Centaur, and the GPS sat high above the Earth. The Centaur then burned to put itself into an elliptical “parking orbit,” then it burned again to achieve the desired near-circular orbit 20,450 kilometers from the Earth’s center (roughly 14,000 kilometers above the surface).

Once that happened, it performed three tasks: It released the satellite, it made a “collision avoidance maneuver” to make sure it wouldn’t accidentally hit the satellite, and then dumped the remaining fuel in its tanks into space for safety.

These events occurred when the Centaur was over Australia, and Kelaher captured them on video!

In the video you can see the plume of gas lit by the Sun (it was 03:00 local time, but the Centaur was high enough up to be in sunlight). Because it’s essentially a vacuum that high up, the gas cloud expands without friction and moves along with the Centaur and satellite. You can see (what I presume is) the GPS satellite moving along with the plume, just to the lower left.

Moving across the sky they appear to pass several well-known astronomical objects, including the fantastic globular cluster Omega Centauri and the spectacular Carina Nebula.

Because the launch time and orbit were known in advance, Kelaher could know in advance to see them … as he had been hoping and planning to for six years!

Patience pays off.

I’ve never seen anything like this, though I once saw a rocket booster burn up in re-entry many years ago, and it was amazing. This would really be something to observe! Rocket launches can create all kinds of truly spectacular and bizarre sights. And I’ll add that you can see many satellites with the naked eye (check Heavens Above for local listings of visible satellites), and it can be a real kick to spot one and identify it.

Going out under the night sky is never time wasted. The rewards are many, and if you do it enough, the bonuses can be pretty nice, too.

Tip o’ the payload fairing to the Ice in Space group on Facebook, and to Suzy Webb in particular.

* Correction, April 21, 2016: I originally misstated that the launch was on April 5.

April 20 2016 11:45 AM

The Future Is Here: A Festival Celebrating Science and Science Fiction

Are you a) a science enthusiast, 2) a science-fiction fan, and γ) live near Washington, D.C.?

Then you’re going to love this weekend: Smithsonian magazine is holding a festival called “The Future Is Here,” from Friday to Sunday, April 22–24. It’s a celebration of science and science fiction and how they interact. It’ll be a lot of fun.

Most of the events are free, but some require tickets (which are on sale now). The speakers range from NASA scientists to actors, writers, and producers of television sci-fi. For example, one speaker is a guy named William Shatner, of whom you may have heard. Also speaking is Chris Carter (creator of The X-Files), NASA Deputy Administrator Dava Newman, explorers Céline and Alexandra Cousteau, Arc Attack (Tesla coils playing music!), and seriously a much longer list of very cool people.*

Also, me. I’ll be there in two capacities. On Friday night I’ll be moderating the 12 Monkeys panel, with co-creator Terry Matalas and stars Amanda Schull, Aaron Stanford, and Emily Hampshire. 12 Monkeys is a new series on Syfy, a part of the network’s notable and in my not-so-humble opinion highly successful campaign to put out some seriously high-quality television shows (like The Expanse).

12 Monkeys is loosely based on the movie of the same name, about a group of scientists from the future who use time travel to try to prevent a global plague that wipes out nearly all of humanity. The first season has already aired, and the second started this past week. It’s a really good show, atmospheric and clever, and I dig it. On the panel we’ll be discussing the mechanics and philosophy of time travel, how the writers keep up with alternate timelines, and how the actors and crew keep up with what must be a bonkers filming situation. Multiple timelines and multiple time eras can’t be easy to track.

12 Monkeys
My character isn't quite fleshed out yet.

Photo by Syfy / NBC Universal (modified by Phil Plait)

In my second role at the event, I’m very pleased to be interviewing Dava Newman on stage, one on one, about NASA: where it’s going, how it’ll do it, what their plans are. I’ll also be giving a very brief presentation on what NASA means to me, introducing several other NASA speakers, and then also bringing in, via Skype, Andy Weir, the author of the best-selling novel The Martian, which you also may have heard of. I hear a pretty good movie was made about it.

I am very much looking forward to the festivities! I’ve been a science-fiction fan my whole life, and (obviously) also a science aficionado. The two are inextricably linked for me, each urging on and inspiring the other. The recognition this symbiosis gets now warms my heart and makes me hope for the future.

In many ways, that’s what both are about.

So please join me and all these fantastic guests for a weekend of looking up, looking out, and looking forward.

*Correction, April 20, 2016: This post originally misspelled Chris Carter’s last name.

April 20 2016 9:30 AM

So Maybe Not Aliens, but How About Comets?

So it’s been a while. Where are we now with the aliens-building-megastructures star?

A quick recap: As you may remember, citizen astronomers combing through Kepler spacecraft data found a very weird star. Kepler stares at thousands of stars looking for dips in their light, indicating a planet passing in front of the star. This is called a transit and is a massively successful way of finding such exoplanets.

Usually, the light from a parent star will have one dip every few days or weeks or so, as the planet orbits it. But the amateurs looking at the data from the star KIC 8462852 found something very different: Lots of little dips happening at irregular intervals, and the occasional big dip. And by big, I mean like 20 percent or more of the star being blocked. That’s colossal, and doesn’t make a lot of sense at first blush; even a huge planet might block only 2 or 3 percent of a star’s light.

The citizen scientists looking at the data were part of a team from Planet Hunters, an effort to get more people looking at Kepler science. They contacted their team leader, Tabetha Boyajian, who then published the data with a series of possible explanations, including perhaps a swarm of comets passing the star and blocking its light. More on that in a sec.

Another explanation is that aliens live on a planet orbiting that star, and are building giant solar collectors to generate the energy needed to sustain an advanced civilization. To be clear, we know this is incredibly unlikely to be the case, but it’s an intriguing idea. SETI even aimed its radio telescopes at the star to see if they could pick up any signals, but nothing so far.

Boyajian herself gave a TED talk about this star, and it’s well worth watching.

Still, Tabby’s Star, as it’s now colloquially called, is intriguing. I’ve never been convinced by the comet explanation. It seems the least unlikely explanation—faint praise!—but a new paper has come out giving it a bit of a boost. The researchers find that a swarm of comets could explain the clusters of smaller dips of starlight. It would take a few hundred comets if they’re each around 10 kilometers across, or a few dozen if they’re 100 kilometers across.

Their explanation actually works pretty well for the small dips, but it still makes me wonder. The comets would be very hard-pressed to explain the two very large dips in light seen in the star, meaning something else would have to be invoked to explain those. That’s not very parsimonious.

And a swarm of comets isn’t a stable thing; after a few thousand years it should break up. For this to work, you’d need a huge object, like the size of Ceres, breaking up for some reason (a huge impact?) with the pieces becoming these comets. Or it could be that we happened to catch the start of a bombardment, a long period of comets dropping down from the outskirts of their solar system, perhaps disturbed by the gravity of a passing planet.

Scientists don’t like coincidences; they’re like a magic wand, too easy to use to solve problems. But they do happen. And it’s worth remembering that we are seeing something very weird happening at this star, something we’ve never seen before, and all the other explanations are even less likely. We might not like picking the least bizarre explanation, but this star is really blowing the curve on what’s normal.

Interestingly, another astronomer found that the star appears to be dimming slowly, over the course of the past century or so at least. I have to wonder if that could be tied to the comets; they tend to be surrounded by clouds of gas and dust, which might contribute to an overall dimming. But other observations showed no signs of these clouds.


So, to answer my first question: Where are we with this star? Still scratching our heads, I think. Comets may explain some of it, but not all. It may be several related things happening at once, or maybe different things happening around the same time. Or it may be just one thing no one has thought of yet.

It’s a mystery, but a fun one. What’s going on? We just don’t know. But more observations (not just of this one star, but as many others as possible, too, to see whether Tabby’s Star is unique), and more people thinking about it are the way to go. The aliens idea may make this seem silly, but the data are real. Something is going on around this star. I don’t know what it might be, but what I can guarantee is that when we do figure it out, it’ll be something pretty amazing.

April 19 2016 12:30 PM

A Sooty Cosmic Spider 

I’m always surprised when I find a picture of a nebula I’ve never heard of before, especially when it’s big and splashy and very cool-looking, as well as scientifically really interesting.

So I got a bit of a shock when I saw this image of IC 417, aka The Spider Nebula, on NASA’s Instagram feed*:

April 19 2016 9:15 AM

Optical Illusion: Are These Lines Moving, or Is This a Spinning Square?

Our brains are a mess.

They evolved step by step, one function added to another in a million small steps that might help in one way, but that conflict with what another part of the brain is trying to do. When you couple that with the fact that our senses bombard our brains with signals, flooding them with input, our ability to make sense of any of the world at all is nothing short of astonishing.

But it doesn’t always work with optimal efficiency, leading to confusion, and sometimes short-circuiting our perception.

That’s why optical illusions are so wonderful. They lay bare these miscues, allowing us to perceive them and understand them.

Here’s a great example of this: Watch this looping animated GIF (adapted from a demo by Michael Bach). You’ll see two sets of parallel lines moving in perpendicular directions … until the green squares pop up.

Motion Binding illusion

Adapted from Michael Bach

Do you see the illusion? At first, the two sets of lines appear to move independently of each other, moving back and forth at a 45° angle, perpendicular to the motion of the other set of lines. When I watch, my brain has no trouble separating them.

But then those squares pop up, and suddenly the four lines are all moving in sync, appearing like the attached sides of a square moving in a circular motion! The illusion is very strong.

This illusion is due to “motion binding.” This is where you see two or more sets of objects moving, and our brains let the motion of one set influence how we perceive the motion of the other. We see the two motions bound together, even if they aren’t.

It’s not a problem when the lines are separate. Those gaps are important, because it’s a clue to our brains that the two sets of lines are indeed different. But cover up the corners, and that piece of information is lost. The brain tries to link them together, and the motion suddenly becomes coherent as a whole.

I’ve seen lots of discussion about this online, but no one points out an important part: the lines themselves. Each line is a single, solid color. That doesn’t matter when the corners are not covered; the lines are moving in and out. But when the corners are covered, our brains interpret the motion as not just in and out, but also side to side a bit, sliding along their own length. But that motion is an illusion. It’s not real. It’s only the green squares covering up the gaps that makes it seem like the lines are sliding.

If the lines were not a solid color, but instead broken up into black and white squares along their lengths, that would be another clue to their motion, and the illusion would vanish, or at least be much harder to sustain (for more about this, read the demonstration on the right column of page 185 of this book).

I find this fascinating, and really engaging to play with. What happens if instead of looking over the whole picture, you instead concentrate on the motion of a single side of the “square”? If I do that, I can see the individual motions again, even when the green squares appear. But my grasp is tenuous, and if I lose my concentration suddenly, it’s a gyrating square again.

Amazing. And a very important lesson: What you see in the world may not be what’s really happening. Our eyes and brains are very, very easy to fool. We see patterns where none exist, no patterns where they do, motions when there are none, and more.

Seeing is not believing. Or at least it shouldn’t be. Remember that when someone reports a UFO, or a ghost, and says, “I know what I saw!” Because I’d be willing to bet they really don’t.

I love illusions, and how they show us not to necessarily trust our senses. Here are some examples that will hurt your brain.

Tip o’ the Necker cube to @nidavellir and to Slate video team member Shon Areih-Lerer for creating that animated GIF.

April 18 2016 11:45 AM

How Do You Get Better Science in TV And Movies? You Have to SEE.

Oh, do I love science fiction on TV and in the movies. I’m grooving on The Expanse, 12 Monkeys, Agents of S.H.I.E.L.D., and more. The science in a lot of these productions may not be perfect, but it’s pretty dang good. Certainly way better than it was even a few years ago.

A big reason for that is SEE: the Science and Entertainment Exchange. This is a program by the National Academy of Sciences—a very prestigious group—to increase the quality of science and the depiction of scientists in the media. I love this idea; most writers of these shows aren’t experts in the science, and when they talk to scientists, they can discover storylines they wouldn’t have even known existed.

The video network Great Big Story just put out a lovely short video showing a great example of this: How SEE got Agent Carter producer Wendy Wimming in touch with physicist Clifford Johnson to add some realism to the second season:

When I watched the second season of Agent Carter I smiled at the physics references; they rang true, and I knew SEE was involved.

I’ve worked with SEE for many years now; they put me in touch with a video game company to help them add real astronomy to the story, I’ve done several panels they’ve put together at San Diego Comic-Con, I’ve spoken at the Director’s Guild in L.A. on a panel they organized about the end of the world (and I got what is shirley the single greatest gift in my life from that), I’ve written for their website, and Rick Loverd, featured in the video above, is a good friend. I even helped him a tiny little bit on his comic book Venus.

So yeah. I’m a big fan of theirs. They do good work, getting more and better science out into the public. And in the end, they help make stories better.

And, as a good doctor once said, “We're all stories, in the end. Just make it a good one, eh?”

P.S. If the Agent Carter storyline of actress-and-scientific-genius Whitney Frost sounds familiar, she was based on real life as well, though I don’t think Hedy Lamarr was infected with a bizarre form of quantum matter.