Bad Astronomy
The entire universe in blog form

Aug. 9 2016 9:00 AM

NASA High Definition Camera Creates Stunning Slo-Mo Rocket Booster Footage

On June 28, NASA test-fired a solid rocket booster being built for its Space Launch System rocket. The test went well … but it wasn’t the only thing being tested.

A sophisticated new type of camera was also getting a shakedown run: It can record very bright and very faint objects all at the same time. The resulting slow-motion footage of the SLS booster test is mesmerizing:

The camera, called NASA’s High Dynamic Range Stereo X (or HiDyRS-X), uses a variation on high dynamic range processing. HDR pictures, when done in the standard way (like in many phone cameras), can show a broader range of brightness. Instead of taking a single picture, the camera takes several at different exposures, then uses software to analyze the images and creates a composite that takes the brightest parts of the scene and uses the shortest exposure for them, while using the longer exposures for fainter parts. When combined, everything looks exposed correctly.

This won’t work for video, at least not easily. Taking multiple exposures takes time, and if you’re trying to see something that moves quickly—like a rocket plume—that’s a problem! This is where the new camera is very clever: it uses onboard technology that exposes each individual pixel separately, so that bright and faint parts of the shot are balanced in each individual video frame.

The results are stunning. A normal video camera shows the rocket plume as being hugely overexposed compared with, say, the engine nozzle (see the image at the top of this article). But in the HiDyRS-X video you can easily see both, allowing for accurate tracing of plume dynamics, which is critical if you want to understand how the rocket engineering affects the thrust.

While I am no fan of the SLS (to say the least), I am still mightily impressed with this footage. A camera like this will be massively useful not just for NASA but in many other applications. In fact it was NASA that helped it get developed; it was created by engineer Howard Conyers under the auspices of the Big Idea Challenge, a design competition looking for innovative, game-changing ideas. It looks like they found a good one here.

Tip o’ the lens cap to Fark.

Aug. 8 2016 9:00 AM

GOP Sen. Ron Johnson: Lack of Global Warming Is “Scientifically Proven.” Yeah, About That …

Last week I wrote about a senior Republican congresswoman, Marsha Blackburn, who not only denies climate change is real but made the bizarre statement that the Earth is actually cooling.

I know, right? But not to be outdone by his colleague in the other chamber, Sen. Ron Johnson, R-Wisconsin, decided to let loose with a stream of nonsense on the same issue in an apparent attempt of what I can only think of as one-downmanship.

On the Glenn Klein radio show on Wisconsin’s WRJN on Tuesday, Johnson decided to let the world know his grasp of science is at best tenuous, and he’s more than willing to grease his fingers. As an example, he said this:

First of all the climate hasn’t warmed in quite a few years, that is proven scientifically.

Oh, senator. If you want to talk scientifically, then the global warming “pause” you’re referring to doesn’t exist. We’ve had nine record-breaking high temperatures globally in a row. The year 2015 was the hottest one on record, beating the previous record-breaking high temperature year of 2014. Every single year of the past 13 years has been among the hottest ever recorded.

“Proven scientifically,” the senator says. Right.

But he’s not done letting loose the zombies of denial. He continues:

So, that’s why they changed the terminology from “global warming” to “climate change.” That covers everything. Climate has always changed, it always will.

This is one of the most egregious of the denier lies, and one of the most aggravating: Changing the framing from “global warming” to “climate change” was a Republican strategy. It wasn’t progressives who did that, it was Frank Luntz, a Republican strategist, who did it to make it sound less “frightening,” the easier to downplay it.


Then he makes a more subtle but still grossly incorrect statement:

… [Measured from ice cores, over hundreds of thousands of years] we’ve had temperature variations of 22.7 degrees. There were men and women 20,000 years ago, but not enough building campfire to produce CO2 to cause those glaciers to recede or to cause those temperature variations… There are greater forces at play.

I’ll admit he does say one correct thing there; surface temperatures measured in Antarctica from the Vostok ice core show a variation of roughly 22° F over time. But note that phrase: “over time.” Natural variations in climate do occur, and no scientist will deny that. As I wrote in the post about Blackburn, the problem is that as humans dump carbon dioxide into the air at huge rates, the speed at which the temperature is now changing is unprecedented. Slow variations are bad enough, stressing the environment and forcing species to adapt; but if it happens too quickly it’s not possible to adapt quickly enough. Rapid climate change can force huge numbers of species to go extinct, and the effect it will have on humanity is profound and terrible.

There’s one other thing Johnson says worth pointing out (though there’s plenty more wrongness to be had in that interview):

… the question is, how much does man cause changes in our environment, changes in our climate, and what we could possibly even do about it?

Actually, that question had been asked and answered. Essentially all the global warming we’re currently seeing now is caused by human activity (without it, the Earth actually would be cooling slightly). Scientists who study climate overwhelmingly agree about that.

And there is something we can do about it:

Vote science deniers out of office.

And hey, isn’t Sen. Johnson up for re-election this November?

Aug. 7 2016 9:15 AM

The Complicated Trajectory to Understand a Comet

In the summer of 2014 the Rosetta spacecraft approached and entered orbit around the comet 67P/Churyumov-Gerasimenko. No mission had ever done that before; humans had sent missions flying past comets, and even one to smash into a comet, but no long-term stay had ever been attempted.

Comets have very little gravity, so the term “orbit” is a bit loose here. Rosetta shifted around the comet, constantly changing its trajectory to accomplish the science needed to better understand the bizarre little wordlet. The European Space Agency released a short video outlining the spacecraft’s path as it moved around, and it’s worth watching:

I like how they highlighted important mission milestones, like when orbit was first achieved, and when the Philae lander was deployed (and when it was last contacted). Part of the mission objective is to sample the environment around the comet; as the ice on the comet is warmed by the Sun, it turns into gas, dislodging dust and small debris from the surface. Observing how this process works will help scientists understand what comets are made of and how they’re put together, and you can see how it zipped around the comet both close and far, exploring these different volumes of space around it.

One big day was Aug. 13, 2015, when the comet achieved perihelion, its closest approach to the Sun (at about 1:50 in the video). The amount of light and heat received was at a maximum, and after that started to dip down. Rosetta kept its distance, in part to get an overview of the comet, but also to keep it far from any bigger (or even eruptive) outgassing events.

In 2016 Rosetta dipped low over the comet, then moved very far away to put the comet between the spacecraft and the Sun, so that the space around it was backlit, the better to see the material ejected. The images it sent to us were dramatic, to say the least.

It also shows the final orbits of the mission, leading up to the biggest day of all: Sept. 30, 2016, when the spacecraft will set itself down on the surface, ending this grand adventure.

But not the grand adventure. Rosetta may have been the first spacecraft to orbit a comet, but it won’t be the last. We’ve learned so much! And part of being a pathfinder is learning how to do such a mission in the first place. It’s not easy, which is a big part of why I’m showing you this video; look how complicated the path was, and imagine how difficult planning it was. But that’s what we humans do, when we so desire: We take the hard way, accept the challenges and risks, and begin the journey.

May this one go on as long as humans look up and wonder.

Aug. 6 2016 9:00 AM

Iridescent Sunset Mammatus

If every there is a Colorado summer sunset that doesn’t leave me standing slack-jawed and awestruck, just turn me into Soylent Green. My wonder and joy will be dead.

This was sunset in late July 2016. Lower-altitude cumulus clouds are silhouetted, but the trailing edge of large anvil-headed cumulonimbus was lit at low angle by the Sun (which had already set behind the Rocky Mountains from my location). Mammatus clouds were forming; weird bulb-shaped clouds that are common in patches, but also sometimes (and more rarely) seen in huge fields across the sky. The low Sun lit only the bottom edges of the mammatus, giving them an eerie glow.

Aug. 5 2016 9:00 AM

Perseid Meteor Shower Peaks Aug. 11 and 12 with a Possible Strong Outburst!

The annual Perseid meteor shower peaks this year on Aug. 11 and 12, with the best viewing after local midnight. The shower is one of the very best of the year, with 60 or more shooting stars visible every hour.

I have a viewing guide below, but first there’s some unusual news: The shower may have a rare outburst, a big uptick in activity, this year!

The Perseids are debris from the comet Swift-Tuttle, which orbits the Sun every 133 years. When it gets close to the Sun, the heat from our star turns the ices in the comet into gas, forming the long tail. Small bits of rocky debris also slough off and trail behind the comet. When the Earth plows into these, they burn up in our atmosphere to form the shower.

However, they’re not alone in space. Jupiter’s gravity tugs on the stream of particles, causing their orbits to shift. Sophisticated computer simulations indicate that this year, the Earth should be plowing through a denser than usual part of the stream, creating as many as 200 shooting stars per hour!

This outburst should occur on the night of Aug. 11 and 12. It’s not clear if it will happen, or when—these things are pretty difficult to predict—so I advise you go out shortly before midnight and stay out as long as you can. If you miss it, don’t fret: The shower will still be nice the next night, too. As I describe below, the later at night you can stay out the better.

So, ready for the viewing guide? Here you go. I’ve adapted the previous year’s guide to be appropriate for 2016. Watching a meteor shower is easy and fun, and I highly recommend it. Even better, the roughly half-full Moon sets around midnight, so it won't be around to wash out the meteors! So get out and take a look.

Oh, one more thing: If you have cloudy skies, don't fret: NASA will live-stream the shower! So you can always watch on your computer.

The Eta Aquarids are another fine shower. Note how the meteors all appear to radiate away from one point in the sky, called the radiant. See below for the explanation.

Colin Legg, used by permission

Perseids 2016 Viewing Guide

For the tl;dr crowd: The best time to go out is Thursday night Aug. 11/Friday morning Aug. 12 after your local midnight. Find a place with wide-open skies, lie back, and look up. You don’t need a telescope or anything like that. The meteors should zip across the sky about once per minute or so on average, appearing to come from near the constellations of Cassiopeia and Perseus in the northeast.

Meteor showers occur when, as the Earth orbits the Sun, it plows through the debris left by a comet (or, in one case, a weird asteroid) that is also orbiting the Sun. Comets are basically dust and gravel held together by water ice, and as the Sun warms the comet, the ice sublimates (turns directly to gas) and the rocky bits are sloughed off. They orbit the Sun in more or less the same path as the comet, and when the Earth rams through them, they enter our atmosphere at high speed, heat up, and glow.

And we get a meteor shower.

Due to perspective (the same effect that makes raindrops always seem to be coming from ahead of you when you drive a car through a rain shower) the meteors appear to come from a point in the sky in the constellation of Perseus, near the W-shape of Cassiopeia. They radiate away from there, so that point in the sky is called the radiant, and the shower gets its name from the constellation.

By the way, I did a whole episode of Crash Course Astronomy on meteors. It’s not specific to the Perseids, but it’s chock full o’ fun science.

Now, on to the FAQ!

When is the best time to watch?

Technically, the meteor shower starts around July 17 and lasts until late August. Realistically, though, it peaks over the week around Aug. 11–13. This year, the best time to watch is Thursday night/Friday morning after local midnight (that’s when your part of the Earth is facing into the oncoming meteoroids and you see more). However, a night before or after will be fine, too. The later you wait in the evening the better, but even a couple of hours after dark will be fine.

How many will I see, and how often?

The Perseids average about 60–100 meteors per hour. I usually see a lot fewer than that because my skies aren’t particularly dark. Meteors are random, in that you may see three in a row in a few seconds, then nothing for five more minutes.

A lot of people have the misconception that you’ll see meteors zipping across the sky everywhere like fireworks. It’s not like that; expect to see one per minute or so. Trust me, it’s still wonderful!

Speaking of which, don’t expect to go outside and see tons of meteors right away. Your eyes take a few minutes to adjust to the darkness (it takes about a half hour to get fully adapted) so give it a few after going out. Patience!

And remember, if there's an outburst, you might see many more! It's worth going out to see.

The Perseids over Denver in 2012. Note how they can be anywhere in the sky, so the wider open a space you can be in, the better.

Thomas O'Brien, used by permission.

What direction should I face?

Up! Seriously, meteors can appear anywhere in the sky (though they tend to head in a direction away from Perseus), so the more sky you can see the better. Try to get away from buildings and trees. I have a spot in my yard with fewer trees and where my house blocks the light from nearby towns. See if you can find something similar.

Do I need a dark sky?

Being away from city lights helps a lot. Many meteors are fainter and get washed out if the sky is bright from light pollution. However, I grew up in the Washington, D.C., suburbs and usually saw quite a few meteors, so incredibly dark skies aren’t critical. Just nice.

Do I need a telescope or binoculars? A camera?

I think this comes up due to movies and TV shows (and commercials in fact) where they show people out in a field looking through a telescope during a shower. But this is a terrible idea! Meteors zip across the sky from random spots, so you want to see as much sky as possible. A telescope only lets you see a tiny part of the sky at once. Bent over an eyepiece, you’re likely to miss everything. It’s like trying to watch fireworks through a soda straw.

Having said that, if you have binoculars or something else, why not use them every now and again just to see the sky? You’re outside, it’s dark, and the wonders of the heavens await! Just be aware you’re trading off seeing some meteors if you do, but scanning the Milky Way with binoculars for a few minutes is totally worth it.

As for taking pictures, getting good shots of meteors can be a bit tricky. I suggest reading the guides at the American Meteor Society, Sky and Telescope, and PetaPixel. What you get out of the effort depends on what you put in, usually. But even inexpensive digital cameras can do the trick.

Meteors, meteoroids, meteorites? What?

Meteoroids are the solid bits of debris. Meteors are what we call them as they shine brightly, ramming through our air. Usually they burn up, but if they make it to the ground we call them meteorites. So a meteorite is a meteoroid that survives being a meteor.

How fast are the meteors traveling?

A typical Perseid is moving at about 60 kilometers/second (35 miles/sec) when it enters our atmosphere. That’s 200,000 kph (130,000 mph)! That’s incredibly fast; rapid enough to get from the Earth to the Moon in just two hours.

Geez, that’s fast! Are we in any danger from the meteors?

Nope. These are generally not much more substantial than snowflakes or grains of sand. They burn up 90–100 kilometers above the ground, far, far above your head.

Perseid from above
How amazing would it be to see a meteor from above? Astronaut Ron Garan caught this Perseid from the International Space Station in 2011.


Are astronauts in danger from meteors?

Not really. The odds of the space station getting hit are incredibly low, even over the course of many years. But in 2011 astronaut Ron Garan got a photo of a Perseid meteor burning up in the air below him. How cool is that?

Why do they leave a smoke trail?

That’s not really smoke; it’s vaporized meteoroid bits! As the meteoroid screams through the air, it gets hot because it’s violently compressing the air ahead of it—when you squeeze a gas it gets hot, and the meteoroid is squeezing the air hard. Bits of the particle melt and blow off (astronomers call this “ablation”) forming the long trail (technically, we call it a “train”) and can take a few seconds to cool and fade.

One meteor got really bright and I thought I saw a puff of smoke that lasted for a few minutes. What was that?

Pushing through our air at high speeds puts the meteoroid under incredible pressure. It can break apart, and the pieces burn up much more rapidly. This can cause a pulse or multiple pulses of light, basically explosions. The meteoroid can disintegrate, creating a big puff of ionized particles that sometimes last for several minutes (this is called a “persistent train”), which then gets twisted in high-altitude winds. It’s rare, but spectacular. I’ve never seen one.

Why are some meteor trains long and some short?

The length of the train depends on the angle of the meteor toward you. If it’s headed right at you it will appear foreshortened, so it looks really short. If it’s headed tangentially from you, more or less across the sky, it’ll appear longer.

Its like someone throwing a ball right at you to catch versus watching two people play catch from the side. Perspective counts.

Can I listen to the shower?

This may seem like a weird question, but the answer is yes, kinda. They happen so high up that any sound they might make will never reach your ears, so in that sense, no.

But, meteors are so hot they ionize the air around them, stripping the electrons from the atoms and molecules. Ionized air makes an excellent reflector of radio waves, and so a meteor will make a radio “ping” as it zips through the sky. You can listen to this live at the Space Weather Radio site. It’s eerie.

I have more info about this in an earlier post.

Where can I get find out more about meteors?

I’m glad you asked. Here are a bunch of links that’ll keep you occupied until the show starts. Enjoy!

Aug. 4 2016 9:00 AM

Senior House Republican Says Earth Is Cooling

With the election coming up, I hear a lot of people making the claim that both parties are the same.

This makes my head explode. The GOP’s platform literally lists out its anti-science stance, from abstinence-only education to “clean coal.” The former has been shown to be worse than useless (abstinence-only education doesn’t teach concepts like condom use and sexually transmitted diseases, so those kids go on to have sex anyway—because they’re human—and wind up with higher rates of STDs and pregnancy), and the latter simply doesn’t exist.

I hardly need to lay this out; when GOP politicians talk, they make their stance quite clear. And that stance is facing firmly away from scientific reality.

As further evidence I give you Rep. Marsha Blackburn, R-Tennessee. She is a senior congresswoman, having been in the House since 2003, and has received nearly $300,000 from fossil fuel interests during that time, so you can guess where this is going.

During the Republican National Convention, the Washington Post held a series of live interviews and had her on with Jay Faison, a conservative philanthropist. In the video, the interviewer asks about climate change, and her response is stunning, even for a GOP Representative:

The nonsense she says starts at 1:15 or so. First off:

Certainly Congress, when Pelosi was the speaker, had a select committee to investigate global warming and then they decided they would make it climate change …

Cripes, this again? It was not liberals who started using the term “climate change” to replace “global warming”: It was Republican strategist Frank Luntz who got that started on the GOP side. Her claim is pure Orwell. Also, those terms have different meanings: Global warming causes climate change.

But she wasn’t done …

… but then they decided to make it climate change, because the Earth is no longer warming. And has not for about the past 13 years. It has begun to cool.

What the WHAT?

I would direct you to this graph of global temperatures:

global temperatures
Global temperatures compared with the average from 1951–80. I'll note this was created by a group initially skeptical of global warming. Click for details.

Berkeley Earth

It’s not just that Blackburn is wrong. It’s that she’s exactly, precisely wrong. She couldn’t be more wrong. Every single year of the past 13 years is among the hottest ever recorded. The years 2014 and 2015 are Nos. 1 and 2, by the way, and 2016 is looking to edge them out.

What she said is pure, unfiltered baloney (and she’s been saying it for a while now). The moderator’s expression and reaction looks like she hit him with a brick; it looks to me that he’s stunned by what she said and not sure if he should rebut her or not. A few minutes later (around the 3:04 mark) he does say something, stating (correctly) that climate scientists would strongly disagree with what she is claiming. So she decides to dig deeper:

The point is, it’s not a settled science. There’s a debate in that arena. And there are those that say it has cooled, it has leveled off. Then there are those who say no I still agree with the hockey stick theory, and I agree with the IPCC. I think it’s still warming. The point being … it’s not something you would say it’s a settled science.

Wow. Actually, yes, the science on the basics of human-driven global warming is settled. There are lots of details left to determine, as there is in any field of science. But we’re making the extra carbon dioxide, we’re dumping 40 billion tons of it into the air every year, it’s causing the Earth’s temperature to go up on average, and that’s having a wide and profound series of effects on the climate. That is the science.

There is no real debate on the science; only nonsense and smears by those who deny the reality of global warming. Sure, there are people who say the Earth isn’t warming, but those people are overwhelmingly not climate scientists. If someone says the Earth is cooling they need to retake middle school science class. And they certainly shouldn’t be in a position of power in the government.

Hockey stick diagram
The hockey stick diagram shows temperatures on Earth are rising more rapidly now than they have in the past 11,000 years.

Marcott et al. (via Climate Desk)

And by the way, the “hockey stick” is not a theory; it’s a set of reconstructed temperature measurements going back thousands of years, showing that the rate the planet is warming is unprecedented for many millennia. Her use of the term "theory" sounds to me like a way to belittle the idea, a common rhetorical ploy.

Hearing all this malarkey from a senior congresswoman is more than aggravating, it’s frightening. Deniers like her spin and deflect and say whatever flies into their heads, and all the while the thermometers creep upwards. And she’s the vice chairman of House Committee on Energy and Commerce, because of course she is.

So to get back to my original point: Yes, there is indeed a vast, yawning gulf between the two parties in many ways, and perhaps none greater than the very real threat of global warming. So when you have a friend who makes that “both parties are the same” equivocation, let them know that that’s just more hot air.

Tip o’ the blinders to Daily Climate and Bloomberg BNA.

Aug. 3 2016 9:00 AM

SpaceX Fires Up a Second-Hand Booster

On May 5, SpaceX launched a Falcon 9 rocket carrying a communication satellite into space. A few minutes later, the automated first stage booster guided itself back to Earth, landing on a drone ship in the Atlantic.

That booster was cleaned up, checked out, refitted, and on July 28, SpaceX performed a full-duration test firing of it at its McGregor, Texas, test facility. Watch!

This test is a very big deal. The entire purpose of bringing the first stage booster back is to reuse it, saving money. Instead of building a new one at a cost of $60 million, it might only cost a few million to reuse one previously flown.

The test was a critical component of that. As you can see, the rocket was held down during the firing to test out how it performed. It apparently went well, but I’m waiting to hear about specifics.

The plan is to fly a mission using a previously flown booster for the first time sometime later this year. SpaceX has plans to reuse a Dragon capsule that was previously used as well; up until now every one flown was new. On top of all that, the first flight of the Falcon Heavy may be later this year as well.

SpaceX has been having quite a year, with several launches so far and the announcement of plans to send an uncrewed Dragon capsule to Mars starting in 2018. Between their progress and that of Blue Origin, things are looking up for commercial spaceflight.

Aug. 2 2016 9:00 AM

Blue Origin Test Flight Was a Successful Failure. Literally, in Fact.

Some good news from Blue Origin: Jeff Bezos, the CEO of the rocket company, reports that the last test flight, where one of the three crew capsule parachutes was intentionally undeployed, was a success.

This was the fourth flight of the company’s New Shepard rocket—literally, it’s the same rocket that had been launched and then landed vertically three times in the past. The rocket is suborbital, which means that it essentially goes straight up, deploys (ejects) the crew capsule, then lands back down vertically using its engine while the crew capsule comes back down via parachute. The whole flight lasts just a few minutes.

For this flight, which was on June 19, one of the main goals was to deploy the crew capsule with only two parachutes, to see if it can still land safely in the event of a single parachute failure. In an email sent out to a mailing list, Bezos reports that the capsule (which was uncrewed) descended at about 37 kilometers per hour using only the two ‘chutes before firing its retrorocket to slow its speed just before touching down. That “took out most of the velocity,” and then a crushable bumper ring absorbed the rest of it for a safe landing.

Blue Origin put together some pretty cool video of the flight:

At 1:50 you can see the rocket itself landing perfectly, right back on the launch pad. At 2:10 the crew capsule parachutes deploy, and then touchdown is at 2:53. I’ll note that when I watched this live on the web I didn’t see the retrorocket fire, and I was concerned the landing was too fast. Even in this video I don’t see it, but when I played the video at ¼ speed, I could see that the dust from the ground starts billowing just before the capsule actually makes contact, so clearly that’s from the retrorocket firing.

Blue Origin also released a couple of pictures of the crushable rings; one shows them under the capsule as its being hoisted up after landing, and the other shows the rings removed. As you can see, the rings were hardly compressed at all, showing that the landing wasn’t nearly as rough as you might expect with one parachute knocked out.

crushable rings on crew capsule
The crew capsule (top) with crushable rings underneath; the rings removed show little damage (bottom).

Blue Origin

This is all pretty good news. There’s a market for suborbital flights like these, both for tourists who want the thrill of falling from more than 100 km up and for scientific researchers interested in the effects of microgravity. Plus, this is also another step along the way for Blue Origin to launch orbital missions, which is far, far, more difficult but also more profitable and important in the long run.

SpaceX has been doing that for a few years now, but Blue Origin entering the arena is good for everyone as well. As long as price competition doesn’t compromise safety, the more private companies going into the space, the better it’ll be. SpaceX has shown space flight can be done for a fraction of what NASA can do it for otherwise, and I suspect Blue Origin will be able to as well. They’re working on their next generation orbit-capable engine and rocket, so the next few years should prove pretty interesting.

My congratulations again to Blue Origin! I do love seeing some of the science fiction I read as a kid becoming reality.

Aug. 1 2016 9:00 AM

The Milky Way Crosses Its Heart … With a Galactic X

You know how we know there’s a giant peanut in the center of our galaxy? Because X marks the spot.

That was a fun thing to write. It also has the advantage of being true.

artwork map of Milky Way
Artwork depicting the Milky Way seen face on. The bulge is the yelow-red ellipse in the middle.

NASA/JPL-Caltech/ESO/R. Hurt

Our Milky Way is a spiral galaxy, with a broad disk 100,000 light-years across filled with gas, dust, and stars. In the center is a bulge of older stars, which was once thought to be more or less spherical. In more recent times it’s understood to be what’s called a “bar,” an elongated shape more like a Tic Tac.

Barred disk galaxies are pretty common. When we see an external galaxy face-on the elongated bar is usually pretty obvious. When we see them edge-on, though, it’s harder to distinguish from a spherical bulge.

We’re inside the disk of the Milky Way, so we see our galaxy edge-on. That’s made the central bar difficult to study in detail. Plus, all that gas and dust in the way is a pain, blocking our view.

NASA’s Wide-field Infrared Survey Explorer, or WISE, detects infrared light, which can get through that dust, so we can see the stars in the center of the galaxy more clearly. In a new study, astronomers found that the stars mark a huge X centered smack dab in the galactic core. That’s the image at the top of this article.

artwork of galactic bulge
Artwork depicting the double-lobed peanut-shaped Milky Way star bulge.

ESO/NASA/JPL-Caltech/M. Kornmesser/R. Hurt

So, what the what? What’s this giant X doing there? A big clue can be found in older observations using the VISTA telescope in Chile. This revealed the stars in the galactic core are arranged in a peanut shape, a two-lobed cloud with a thick neck between them. If you were above the Milky Way, looking down, that peanut shape would just look more or less like an elongated bar, but from the side the peanut is more obvious.

banana orbits of stars
Plots showing various possible banana-shaped orbits of stars seen edge-on. 1 kpc = 1 kiloparsec = 3,260 light-years.

Portail, Wegg, and Gerhard

It turns out the stars in that part of the galaxy don’t just orbit the center in circles like planets around the Sun. Instead, the overall gravity of the other stars in the bulge distort their orbits into weird shapes. Seen from the side, these orbits can look banana-shaped, or move up and down in complex patterns. Stars distributed all along these orbits trace out the peanut shape.

So why the X? That’s because the peanut is made of stars, and so it’s “transparent”; we can see stars all through it. When we look near the edges of the peanut we see more stars than when we look through the middle (an effect very similar to limb brightening). That’s what forms the X. Think of the two lobes like two cones tip to tip; the edges of the cones form an X. It’s the same sort of thing in the galaxy.

But there’s more! It’s hard to tell, but the two arms of the X are actually bigger on the left than on the right (this can be seen better in Figure 1 in this journal paper). That’s because that side of the peanut is closer to us! The center of the galaxy is about 26,000 light-years away, and the peanut is about 14,000 light-years long. Not only that, but it’s rotated away from us a bit; we see it nearly along the long axis but spun around by about 27°. That means the near side of the peanut is more than 10,000 light-years closer to us than the other side, making it look bigger. It’s pretty rare that we see such big structures close enough to us that perspective makes a difference in their size!

This has implications for the evolution of our galaxy. This structure is not terribly robust and would fall apart if we merged with another big galaxy; this means the Milky Way hasn’t suffered a large collision for many billions of years (we’re currently eating several smaller galaxies now, but those are far more gentle events—for us at least, not so much for the cannibalized galaxies). The dynamics of the stars in the bar also give clues to how they formed, and how they’ve evolved over the eons, too.

This is all pretty neat and shows that there’s still a lot we have to learn about our own neighborhood, cosmically speaking. A lot of this research depended on having the right tools for the job; specifically infrared telescopes to pierce the dust and powerful computers to calculate the very complicated orbits of the stars in the peanut.

Not only that but another advance that was critical to all this was … Twitter. Yes, seriously. One of the people working on this, Dustin Lang, created a website with the WISE images on it. He tweeted about it, and it caught the notice of astronomer Melissa Ness, who saw the X shape and realized what it meant, leading to their collaboration.

Social media indeed.

Astronomers are pretty good at rolling with the times. New tech and new techniques are part of the job. And when used wisely (har har) they can lead to some pretty beautiful insight into the Universe.

July 31 2016 9:15 AM

Help Make Women NASA Lego Minifigs a Reality

Quick: Name a female scientist.

Can you think of one? Folks reading my blog are probably more bent toward science, so I suspect the odds are better than if you ask that same question of the public. It’s been done, many times, and most people come up with Marie Curie. If you ask them to name a living female scientist, they come up empty.

That needs to change. Women have made a huge contribution to science, and the way we marginalize them is atrocious.

That’s why MIT news editor and science writer Maia Weinstock proposed the creation of a female scientist Lego minifigure set. The set would feature notable women: Margaret Hamilton, Katherine Johnson, Sally Ride, Nancy Grace Roman, and Mae Jemison, all of whom had critical roles at NASA.

Minifigs like this are very popular, and could be a great gift for boys and girls. And it would raise awareness of these important role models in NASA history and in science; something I’m all for.

This set does not yet exist; it’s been proposed and needs 10,000 supporters to go to the next step of being officially reviewed at Lego HQ. So sign up (it’s free) and give them a thumbs-up. It would be great to see this set get into the hands of thousands of kids (and, I’d wager, not a few adults) across the world.

Thanks to my friend Bonnie Burton for letting me know about this. Go read her article about it, too!