The entire universe in blog form

Jan. 31 2015 7:30 AM

So, About That Huge Discovery Last Year About the Young Universe...

Well, this is disappointing. A team of astronomers announced last year that they thought they had strong and direct evidence for cosmic inflation in the extremely early Universe. But, after follow-up analysis, it turns out the evidence is far weaker, and it appears inconclusive one way or the other.



OK, so what’s the scoop? First, here’s the announcement from last year when it was thought that the evidence was really good. The details are there.

But here’s a summary: Right after the Universe formed, it’s thought that it underwent an extremely short (to us) period of rapid growth, way faster than the usual cosmic expansion we see today. This event is called “inflation”, and it explains a variety of conditions in the Universe today that would be pretty hard to understand without it.

The problem is, the evidence for inflation is indirect; circumstantial. It explains stuff we already see pretty well, but it also makes predictions about the Universe, too, but we haven’t seen that evidence yet. For example, inflation would have created ripples in the fabric of spacetime, called gravitational waves. These ripples would affect matter in the Universe, and that would in turn affect the light we see coming from the early Universe.

Until last year, that effect hadn’t been seen. The big announcement was that, using a telescope in Antarctica called BICEP2 (Background Imaging of Cosmic Extragalactic Polarization), that evidence had finally been seen. It made a big splash.

The problem comes in when the astronomers looked at things that might mimic the signal they were looking for. For example, dust (long, complex carbon-molecules that are much like fireplace soot) floating in space can look very much like the signal BICEP2 was seeking. The astronomers knew this, and used data from the ESA mission Planck to investigate it. Planck measured the amount of dust lying along the direction BICEP2 was looking, and the astronomers concluded the amount of dust in their line-of-sight was low. The signal they saw, therefore, must be from inflation.

And here’s the bummer part: They were using preliminary Planck data. When better data from Planck were released, the astronomers used that, and found that the amount of galactic dust in their view was much higher than they previously thought. That weakens their case considerably.

The bottom line is that they do still see some evidence for gravitational waves affecting the light from the early Universe, but it doesn’t look like it rises to being statistically significant, and it’s certainly not as strong as they first thought.

In other words, they cannot say if they have direct evidence for inflation or not. The new results neither prove nor disprove inflation. They’re inconclusive. The observations may all be the result of dust in our galaxy, or it may be that there is some excess signal caused by inflation. Given the current data, we just can’t say.

On a personal note, I reported on this last year as straight news. I assumed that such an announcement had been vetted and the results peer-reviewed. They hadn’t been at that time. As such, I think it’s up to the scientists making the claim to make that clear, and to be more circumspect in their announcement… just as it’s up to those of us reporting on big news to be skeptical and make sure that the process of peer review has been fully respected. That’s on me, and I blew it.

Mind you, I don’t necessarily have a problem with big announcements that are made when the scientists themselves aren’t sure what they mean. Specifically, I’m remembering the faster-than-light neutrino announcement, when the scientists said, basically, “Look, we’ve investigated this as much as we can, and we know it sounds crazy, but our results seem to say that FTL particles are possible. What did we miss?” They were very skeptical, and were asking for others to pitch in and see what they found. It turns out there was a loose cable in the equipment (yes, seriously), that messed up their timing experiments.

There were missteps in that whole mess, but overall I rather like the way it went. They had weird results, they couldn’t explain them, they asked for help, and a culprit was found. Next!

In the case of BICEP2 it was tougher because the results were very esoteric. Doubt was cast relatively quickly on the results, and I watched as rumors flew. I wanted to write a follow-up and say things may not be as they seem, but it was hard to separate fact from speculation. I decided to wait until there was better evidence one way or another. And here we are.

And there’s a final irony here: This new announcement was made by the BICEP2 team, but their results aren’t yet published. They’ve been submitted to a physics journal, and the Planck data they used will be made public next week. So even these results aren’t peer-reviewed yet!

The difference, though, is that this is not a paradigm-shifting announcement, but a retraction. The bar is set lower for such things, so I feel safe enough reporting on it. If, however, someone else comes along and says the retraction needs to be retracted, well, we’ll deal with that if it comes up.

Science is messy sometimes, and it’s made messier by the need and pressure to announce results… and the need and pressure on some of us to write about them. We all need to be more careful in the future.

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Jan. 30 2015 7:00 AM

Meet the New Boss, Very Much NOT the Same as the Old Boss

For those of you who don’t follow me on Twitter, I recently linked to an article that I think is very important. It was written by my friend Hank Green, about the reactions to his recent interview with President Obama.

Hank, as you may know, makes amazing YouTube videos about all manners of topics, with the overarching goal of making the world a better place. This isn’t some treacly greeting-card sentiment; Hank (and his brother John, and their team of amazing young people creating videos) honestly and openly want everyone to be better people. Their motto is “Don’t Forget to Be Awesome.” And they mean it.


Hank, along with YouTube creators Bethany Mota and Glozell Green, interviewed the president, asking him questions that were important to their audience. These included the government’s use of drones, net neutrality, Boko Haram, and racial tension. These questions were unflinching, unapologetic, and discussed without the manufactured “both sides” baloney so common in mainstream media.

The reaction to this by some of that same media was as predictable as it was maddening: disbelief and derision. This is what inspired Hank to write his article. I strongly urge you to read it.

Hank calls these older news sources “legacy media,” which is an interesting term. He describes how these current news media inherited their positions of popularity, as opposed to earning it; they’re not the same venues they once were. A lot of their inroads into our society, their ability to get their message out, is based on their past when things were very different.

And the trust they rely on now has, in many cases, been squandered if not cynically exploited and outright betrayed. The 24-hour news cycle is a huge factor in this, I think; that is a lot of time to fill, and nonsense loves to occupy that space. But corporate ownership is a huge part of the problem, especially when the owners are dogmatic ideologues with an agenda.

Apropos of that, one of my favorite parts of Hank’s article was his response to a tweet by Rupert Murdoch. The head of News Corp. (the right-wing company that owns Fox News) tweeted this:

Hank’s response was perfect. Perfect.

As Hank points out in his article, the average age of Fox viewers is not exactly young. Young folks in high school and college don’t get their news from Fox (or CNN or even MSNBC); they’re far more likely to get it from The Daily Show, from links on social media, and on YouTube.

It’s incredibly trite, but it’s true nonetheless: The future is online. A big chunk of the legacy media still haven’t quite figured this out. They just slap their printed or TV content online and call it good, but that’s not the way things work (or, at the least, it's not enough). And they’re starting from the wrong premise anyway. Younger folks don’t want to see five old rich white guys yelling at each other about women’s rights. They want a thoughtful take on it, from people who represent them better.

People like Hank, Mota, Green, and so many others have spent a lot of time being themselves online, and have built a huge capital of trust. That’s why their audience numbers in the many, many millions.

It’s not too late for legacy media. All they have to do is win our trust back. But trust is earned, not given, and earning that trust is hard work, something I don’t see too many in the old school doing much of. Resting on their legacy is how they got to this dying cul-de-sac in the first place.*

I have no specific solutions, no road map for legacy media to save themselves. This is new territory, and it's being mapped out as it's being discovered. Maybe we just have to wait for the old media to die off ... but that’ll take a while. They still have a lot of money and a maniacal grip on a lot of politicians.

But there’s hope; the president did speak to this new group, and he did reach their younger audience.

What I can hope for is that an entire new generation will reach their adulthood having grown up under the tutelage of this new wave of media and absorb those principles. All they need to do is don’t forget to be awesome.

I’ll leave you with this: the presidential interview. It’s really quite good.

*I’ll note that Slate started as a totally online magazine, which is one of the reasons it’s still going strong, and one of the reasons I was happy to hitch my wagon to them. They understand online culture, and don’t carry the baggage of Old Media.

Jan. 29 2015 5:37 PM

Crash Course Astronomy Episode 3: Cycles in the Sky

You live on a whirling ball of rock and metal. As it spins it also revolves around the Sun, and all this is set in a backdrop of thousands of visible but much more distant stars … and on top of that, there are other planets in the solar system moving around as well.

What does all this look like? Why, that’s the very topic of Episode 3 of Crash Course Astronomy: Cycles in the Sky.


When I sat down to write the syllabus (and later the scripts) for this series, the topic of motions in the sky was one I approached with a bit of trepidation. It’s not easy for most folks to picture how all this works; it can be hard to visualize what’s going on, especially when you’re changing your viewpoint from what’s physically happening (the Earth is spinning, the Earth is tilted, the Earth is moving around the Sun) to what you’re seeing from the Earth (stars rise and set, some stars are forever below the horizon from your latitude, stars change their position over the year).

I hope this episode makes this a little bit easier to understand. If it’s still hard to grasp some of this, that’s OK! It’s always hard at first; it was hard for me. I’ve been doing this a long time now though, so I have a lot of experience going outside and seeing how all these celestial gears fit together. It’s actually a fascinating feeling, looking up and knowing that everything is in motion, and it’s all working under the rules of gravity, momentum, geometry … things we can understand and predict. All the parts are working!

And you can be a part of this too. Go outside and look up. And not just tonight, but tomorrow, and the next night, and the next. Keep looking up. Get to know the night sky, its starry denizens, and its motions. It really is an amazing experience.

Wanna watch more Crash Course Astronomy? The playlist is on YouTube.

Jan. 29 2015 7:30 AM

Laser Rocket Aurora!

This is one of the coolest pictures I’ve ever seen. And bonus: It’s science!

Geez, where to start? OK, this is the Poker Flat Research Range in Alaska, where NASA launches what are called sounding rockets. These are not as big as rockets you might be used to, but they’re still hefty enough to get a payload up as high as 300 kilometers.


On Jan. 26, 2015, four such rockets were launched. In this wide-angle composite picture, you can see the fiery trails of the rocket as they headed skyward (I suspect the exposure started late or was interrupted for the launch on the right, since it starts already off the ground).

In each, you can see where the first stage booster cuts out, and the engine glow gets much dimmer. Then, higher up, the second stage ignites, propelling its payload even higher. The first stage booster continues up on a parabolic arc, then begins to fall. If you trace those arcs down, you’ll even see the impact points on the ground! That’s pretty wild.

The weird feathery glow is part of one of the scientific experiments launched. Called MIST, for Mesospheric Inversion-layer Stratified Turbulence, it releases a compound called tri-methyl aluminum tracer, which creates white expanding clouds. The shape of the cloud can be used to measure the amount of turbulence in the mesosphere, the layer of atmosphere about the stratosphere. The experiment was done in part to see how various molecules in the air are transported vertically in the upper atmosphere.

On the left you can see a green beam; that’s a powerful laser shot up into the air to measure atmospheric conditions at different altitudes.

Of course, the green glowy stuff everywhere is the aurora. And finally, the streaks in the sky are stars! These were time exposures, so the stars moved during the photographs, circling the north pole of the sky (called the celestial pole). Normally you’d see Polaris, the North Star, right in the center of those arcs, but it’s hidden by one of the TMA clouds.

I love science, I really do. But sometimes, I have to wonder: How much of that is because people get to do really, really cool stuff like this?

Tip o' the nose cone to Wigi Tozzi for the link to the video.

Jan. 28 2015 11:44 AM

SpaceX Drops Lawsuit Against Air Force

Last year, the space technology company SpaceX sued the U.S. Air Force over what it saw as an unfair practice; the USAF gave a “sole source” (uncompeted) contract to United Launch Alliance for a series of rocket launches for national security satellites. SpaceX said it had earned a right to be at the table to bid for such contracts. At the time, though, the problem was that the SpaceX Falcon 9 rockets had not been rated and approved for such missions.

The disagreement appears to have been settled: SpaceX has dropped the lawsuit, and for its part the USAF has agreed to help “complete the certification process in an efficient and expedient manner.” It’s also agreed to open up future launches to competitive bids while still maintaining existing contracts with ULA.


This sounds like a decent solution to me. SpaceX has been going gangbusters lately, and if there are no problems going forward (and it’s rocket launches, so you never know), then the Falcon 9 should be a competitive vehicle for the government to use for some of its necessary launches. ULA launches Delta and Atlas rockets, which are great and very reliable vehicles, but pricy.

Right now, the Delta IV Heavy is the most powerful rocket currently in use anywhere, capable of getting nearly 30 metric tons of payload to low Earth orbit, or LEO—that’s why it was used for NASA’s first Orion capsule test launch. The Falcon Heavy, due for its first test flight later this year, will have much higher payload capacity, putting 53 metric tons into LEO.

Once the Falcon 9 is approved by the USAF, I’d think that would pave the way for a similar process with the Falcon Heavy. SpaceX is confident it can launch the Falcon Heavy for a much lower cost than the Delta IV Heavy, too. Pricing, especially when it comes to government contracts, can be very tricky, so I’ll be interested to see how that pans out.

Taking a step back, the good news is there will be competition for launches, and that’s A Good Thing. It keeps companies on their toes, and tends to drive prices down. I’m all for competition, as long as the playing field is even, with no arbitrary (or political) roadblocks thrown in the way. 

One thing I’m still curious about: ULA uses a Russian-built RD-180 engine for their Atlas V first stage. Given Russia’s antics lately, that makes me uncomfortable. However, there’s news that ULA is partnering with rocket company Blue Origin (founded by Amazon’s Jeff Bezos) to build a replacement engine. That’s cool—for a short time a judge laid an injunction against ULA from using the Russian engines, though that was lifted soon thereafter. But Blue Origin is notoriously secretive, so it’s hard to comment on its ability to deliver. I rather hope that works out; again, more competition is better.

As an aside, Orbital Sciences Corp. (which has successfully—and not so successfully—launched rockets to resupply the space station) announced it is merging with rocket engine company ATK. Clearly, there's burgeoning business off-planet.

And on top of all this, very soon there will be American human-rated vehicles once again capable of taking humans into space. A lot of people are lamenting our current situation, but I remind them: This drought of American-launched human spaceflight is going to end soon, and when it does, there very well could be a solid future in space ahead of us.

Jan. 28 2015 7:30 AM

AMAZING Halo Display

Over the weekend I posted an amazing and lovely picture of a sun halo, taken in Sweden. That prompted Kalle Centergren, a self-proclaimed science nerd to send me a photo he took of a halo he saw skiing in Austria.

That’s the photo above, showing an incredible array of optical effects: The 22° halo, parhelia, tangent arcsparhelic circle, a supralateral arc, a Parry arc, a circumzenithal arc, possibly a 46° halo, and probably others I’m not even sure of. That is one of the craziest and most vivid displays I’ve ever seen.


But it gets better: Centergren took video, including some using a drone:

Seriously, right? I expect there was a lot of small snow crystals in the air, suspended over the slopes, creating all those ridiculously beautiful effects.

I went skiing once and tore my ACL. Centergren goes skiing and gets some of the most incredible halo footage I’ve ever seen. Seems fair.

Also, this made me laugh: I noticed that in the drone footage there’s a lot of what looks like detector noise; white specks that flash all over the field. I'm used to seeing this in astronomical data taken right off the telescope; they're caused by cosmic rays, little particles zipping though space that slam into the detector and deposit their energy behind. They’re a massive pain when you’re trying to observe faint objects; you have to go through a lot of careful processing to get rid of them.

So of course that was my first thought when I saw the footage; it's what I'm used to. But that's not at all what those flecks are: They're actually snow crystals blowing around in the air, the very same crystals causing the halo and other optical effects! They appear bright because they're near the camera, and flashing in the sunlight as the camera looks toward the Sun. 

There's an old expression in skepticism: When you hear hoof beats, think horses before you think zebras. In this case, my brain is trained to listen for zebras!

It goes to show that your brain can be easily fooled, even when nothing is really trying to fool you. It just happens. That's always worth keeping in mind.

Jan. 27 2015 11:41 AM

Astronomers Find Ancient Earth-Sized Planets in Our Galactic Backyard

Astronomers have announced what may be the most interesting exoplanet discovery yet made: five planets, all smaller than Earth, orbiting a very ancient star. And I do mean ancient: Its age is estimated to be more than 11 billion years old, far older than the Sun. These are old, old planets!

There’s a lot going on here, as far as the science goes. Let me explain. No, there is too much. Let me sum up. Here are the bullet points:

  • The planets were found using the Kepler space telescope, which uses the transit method: If a star has planets, and we see those orbits edge-on, the planets pass in front of their star as seen from Earth. This blocks a bit of the light, and we can measure that. The amount of light blocked (compared with known properties of the star like its size) tells us how big the planet is. The length of time it takes the planet to transit the star also gives us its orbital period, orbital size, and an estimate of its temperature.
  • The star is called Kepler-444. It’s a bit cooler, more orange, and smaller than the Sun (a K0 dwarf, if you want the details), and is about 117 light-years from Earth. That’s relatively close! Amazingly, it’s actually a triple-star system: There’s a pair of cool red M dwarfs orbiting each other, and the pair in turn orbits the K star. The binary is about 10 billion kilometers from the K star, about twice the distance Neptune is from the Sun.
  • The five planets orbit the primary K star, and are called Kepler-444b up to Kepler-444f. All five are smaller than Earth, and get bigger in order with their distance from the star: Kepler-444b has a diameter of 0.403 Earth, Kepler-444c is 0.497 Earth, d is 0.530, e is 0.546, and f is the biggest at 0.741 our home planet’s size.
  • The planets are not in any way Earthlike! The system is very compact; all five planets are quite close to their parent star—even the most distant one, planet f, is closer to its star than Mercury is to the Sun—and therefore pretty hot. They all orbit the star in fewer than 10 days. They’re pretty well cooked.
  • The system is very old. This was determined using a method called astroseismology, a bit like using earthquakes to observe the Earth’s interior. In this case, the surface of the star vibrates, like standing waves in a bathtub or the way a drumhead vibrates. The character of these waves depends on a lot of the physical properties of the star: its density, mass, surface gravity, size, and age. Very careful observations taken over many weeks were used to get the astroseismological results, and the age was found to be about 11.2 billion years, give or take a billion years. (I’ll note that in part this work was funded through the Pale Blue Dot project, which lets people adopt a star for a small fee that goes toward astroseismology research. Previously, the smallest exoplanet found used research funded through this group, too! And someone named Brian Finley had adopted Kepler-444, so congrats to him, too.)
  • Assuming the planets formed along with the star—a reasonable assumption—these planets have been around a long, long time. The Universe itself is 13.8 billion years old, and the Milky Way galaxy somewhat younger. These stars and planets formed when the Universe itself was young. Put it this way: When the Sun and Earth formed, these planets were already older than the Sun and Earth are now.

So what does all this mean?

Quite a bit, actually. For one, until now we weren’t sure just how old planets could be. We’ve found some Earth-sized planets older than us, but none this old.

Initially, the Universe was almost all hydrogen and helium, with the heavier stuff coming later. The iron and nickel in the Earth, for example, were formed in supernovae, massive stars that exploded billions of years ago. As the Universe ages, it gets more and more of these elements as more of these big stars explode.

When Kepler-444 formed, there were relatively fewer of these heavy elements, and spectra of the star confirm a paucity of elements like iron. We’ve discovered enough exoplanets now that we see an interesting relationship between heavy elements and planets: Gas giants (like Jupiter and Saturn) tend to form around stars that have more heavy elements; these elements aid in the formation of larger planets. But when you look at smaller, more Earth-sized planets, that relationship goes away. Smaller planets form around stars that have lots of heavy elements, and they also form around stars that have relatively few.

The Kepler-444 system supports this. A gas giant planet would’ve been seen, so it looks like these five planets are all it has (or the biggest it has), and each is small and presumably rocky.

But what of life?

Let me remind you, these planets are flippin’ hot. The coolest most likely has a surface temperature way above the boiling point of water. I wouldn’t think there could be life there.

But don’t be so specific. Take a step back and realize that what this means is that Earth-sized planets could form around Sunlike stars even 11 billion years ago! That may have profound implications for life.

You may have heard of the Fermi paradox: If life is easy to get started on planets, then where are the aliens? We do know that life formed on Earth not too long after the planet’s crust had cooled enough to support it. Let’s say it takes 4 billion years for those protozoa to evolve and build spaceships. It turns out that, even with the vast distances between stars and limiting your ships to far less than the speed of light, you can colonize the entire galaxy in just a few million years. That’s far less than the age of the galaxy.

Perhaps you see the problem. If planets like Earth formed 11 billion years ago, and happened to form at the right distance for more clement conditions on the surface, life could have arisen long enough ago and started building spaceships long before the Earth even formed! They’d have planted their flags on every Earth-sized habitable planet in the Milky Way by now.

Where are they?

How long have aliens been around? Assuming any exist in the first place ...

Photo by Pictures/Phil Plait

We don’t know. There are too many “maybes.” Maybe Earth is special in some way that made life easier to form here. Maybe you need iron and nickel to build spaceships (but even then there are planets a billion or two years older than us that would’ve had plenty of such elements). Maybe evolution doesn’t always work its way to intelligence. Maybe every civilization advanced enough to manipulate its environment did so to its own detriment (cough cough). Maybe they blew themselves up. Maybe they’re out there but so advanced we don’t even recognize them.

Maybe we’re just the first.

That’s always been an idea in my back pocket to explain the Fermi paradox. Someone has to be the first. But that’s a bit tougher to swallow when you see rocky planets that are more than twice as old as our own home planet. Eleven billion years is a long time.

Clearly, we just don’t have all the information yet. We’re just getting started here! We’ve discovered thousands of planets orbiting other stars, but there are probably billions of them out there. Billions! We have a lot more data to collect, a lot more information to analyze, and a lot more thinking to do before we can solve this particular mystery.

But we’re working on it. Kepler-444 and its five, small, melted, ancient worlds are just one small piece of a puzzle that is vast and deep. And they’re a good start.

Jan. 27 2015 7:00 AM

Rosetta Catches a Comet’s Snowflakes on Its Tongue

I’ve seen a lot of stuff when it comes to space science and astronomy, and sure, I’m easily excited about it all … but still, it takes a lot to get me to boggle at something.

So this is me, boggling: This photo below shows grains of comet dust caught on the fly by the Rosetta spacecraft!


Yeah. That is very, very cool.

To be more accurate, they’re the remains of comet dust caught on the fly by the Rosetta spacecraft. OK, let me explain.

Comets are essentially dust, gravel, and rocks packed together by various types of ice. Generally speaking, we’re talking water, carbon dioxide, ammonia, carbon monoxide, and other things that are usually gaseous on Earth, but which are frozen in the depths of space.

Lots of comets orbit the Sun on long, elliptical paths, taking them out into the black, then back in closer to the Sun. As they near the Sun, the ice turns into a gas and blows off, and the other junk making up the comet are blown into space as well.

The Rosetta spacecraft is currently following along a comet, called 67P/Churyumov–Gerasimenko. It orbits the Sun once every 6.5 years, going out as far as Jupiter’s orbit (it’s called a Jupiter-family comet, in fact, a member of many comets with similar orbits), dropping down to just outside Earth’s orbit. As I write this, the comet is about 370 million kilometers from the Sun, a bit more than twice Earth’s distance, and still outside the orbit of Mars.

Still, that’s close enough that it’s already becoming active, and we see streams of gas flowing out of it. That means dust particles are coming off too. The thing is, “dust” is a somewhat generic term for tiny flakes of stuff that can have wildly different compositions. Rosetta is in the unique position to find out what 67/P’s dust is made of. So engineers and scientists gave it a shot.

That shot is COSIMA, the Cometary Secondary Ion Mass Analyser. Have you ever been in a snowfall and caught snowflakes on your tongue? That’s COSIMA, except it has a plate exposed to space instead of a tongue, and instead of snowflakes it’s catching, well, comet snowflakes.

When 67/P was still more than 450 million km from the Sun, and just 30 km from the comet, Rosetta caught several flakes of material from the comet. They impacted the plate at speeds of just 1–10 meters per second, roughly bicycling speed. The photo above shows two such specimens (the scale bars represent 500 and 300 microns, where a human hair is roughly 100 microns wide).

When they hit the plate they fragmented. If there had been lots of ice in them, they would have been held together better and wouldn’t have shattered, so right away this tells us the flakes were dry (not like Earth snowflakes at all). They also have a high sodium content, which matches lots of other interplanetary dust particles, particularly meteoroids that burn up in our atmosphere during meteor showers. We know those come from comets, so that checks out! This means we’ve actually found a sample of the parent material of meteor showers. Cool.

But what’s also interesting is what this means for the surface of the comet. These particles were emitted when the comet “turned on” again, getting close enough to the Sun to become active. Scientists think these grains were actually left over from the last time 67/P came ‘round the Sun. As the comet began to head away from the Sun, the flow of gas outward weakened, and wasn’t strong enough to lift dust away. That material then sat on the surface, and was lifted off as the outflow became strong once again a few months ago.

That outer mantle of older dust will be shed, and then more stuff deeper down will start to get flung away. When this happens the dust content may change, possibly showing us other types of material as well. Rosetta will be around for that; it will follow the comet for many more months as it gets to its closest point to the Sun (called perihelion). The comet should become more active, and we’ll get to investigate what lies beneath.

That to me is incredibly exciting. We know a lot about comets, but the devil’s in the details, and every comet is different. Heck, even a single comet changes a lot over the course of a single orbit, so by monitoring 67/P for several months, we’ll learn a lot about these weird beasts. And that’s the whole point.

Jan. 26 2015 7:00 AM

Comet Close-Ups Reveal an Alien World

After a 10-year voyage, the Rosetta spacecraft entered orbit around the comet 67P/Churyumov–Gerasimenko in August 2014, the first time such an achievement had ever been made. Most of the images made public at the time (and since) were from the wide-angle NAVCAM instrument, and only a handful of the higher-resolution OSIRIS camera pictures were released. 

But now the first results from the observations have been published, and quite a few close-up images from OSIRIS have been revealed … and they’re spectacular. The comet is a bizarre, alien place, where our notions of up and down get stymied, and where our “common sense” (from having grown up on a vast, heavy-gravity, be-atmosphered planet) is likely to betray us.

Here are some of those pictures that caught my eye.

Jan. 25 2015 7:45 AM

His First Halo

Swedish astrophotographer Göran Strand took that picture above. It shows a halo around the Sun, replete with parhelia, over Lake Storsjön. That’s his son in the photo.

Besides being extremely beautiful and poignant, it’s also just an astonishing shot. Strand used a 14mm wide-angle lens, which he needed because the full halo is 44° across, a quarter of the way around the horizon. A lens like that really compresses distance, so I’d guess his son was standing right in front of him.


Halos likes this are relatively common. They’re due to flat hexagonal ice crystals in the air. As sunlight enters a crystal it gets bent, refracting as it enters and as it leaves the faces of the crystal. The light gets bent by a total of about 22°, so crystals that distance from the Sun along your line of sight bend the sunlight toward you. Crystals closer to the Sun bend the light away from you so it’s darker inside the halo. Depending on the exact orientation of the crystal, some of the light gets bent more than 22°, so ice outside that 22° bright ring also bend light toward you, though not as strongly, so the halo fades away outside the optimal 22° angle.

When I say “degrees”, I mean an angular distance on the sky, where 90° is the angle between the horizon and the zenith, straight overhead. Your outstretched fist is roughly 10° (I have big hands, so for me it’s more).

The light forms a circle because that shape defines a constant distance from a point; for a halo that point is the Sun (the center of the circle), and the ice crystals 22° away from it fall along the circle of that size.

As it happens, red and blue light get bent by different amounts as they enter and leave the ice crystals; red light is bent a wee bit less, so the inner edge of the halo is redder and the outer part bluer. You can see that in Strand’s photo.

Parhelia—also called sundogs—are also caused by the hexagonal crystals. As the crystals fall through the air they align flat, face down to the ground. When the line between the Sun and crystal is parallel to the horizon, a lot more light gets bent toward you, so you get really bright spots on the halo on opposite sides.

It looks like he has a sun pillar in there, too: a vertical shaft of light caused when the flat crystals are slightly tipped, reflecting light toward the observer. That can only happen with crystals seen directly above or below the Sun.

I’ve seen halos and parhelia I-don’t-know-how-many times. Dozens certainly. Hundreds? Maybe. I look up a lot. If you haven’t ever seen this incredible and lovely display in the sky, then you know what to do.

And check out more of Strand’s photography. I’ve featured a lot of his work on this blog, and you’ll see why.