Bad Astronomy
The entire universe in blog form

Aug. 15 2016 9:00 AM

Chemtrails? Nope.

I’ve spent a lot of time debunking silly conspiracy claims in my time. NASA faked the Moon landings, the Mayan calendar predicted the end of the world in 2012, a mysterious planet named Nibiru would wipe out life on Earth in 2003, the government created fake snow in Atlanta that wouldn’t melt and scorched when burned … I’ve even debunked government officials who claim other government officials are covering up conspiracies.

So when I say I haven’t bothered debunking chemtrails because they’re too goofy even for me, you can glean how I really feel about them.

Still, a handful of people are extremely devoted to the idea that the government is spraying us with chemicals from airplanes, and what you think are simple contrails are actually high doses of mind-altering (or climate altering) chemical compounds meant to keep us under control, I mean, come on, wake up sheeple!

Sigh.

In fact, when you see clouds coming from airplanes they really are just the product of condensation of water vapor. But why let facts get in the way of a good conspiracy?

Still, it’s worth trying. That’s why scientists from the University of California–Irvine and the Carnegie Institute got together and researched the topic. They knew they wouldn’t convince the conspiracy theorists, but having a solid source of objective science might help inform the public discourse.

They surveyed hundreds of experts in contrails as well as those who study atmospheric deposition (how various chemicals fall to the ground from the air), presenting them with the evidence provided on various chemtrail websites (mostly in the form of photos of airplane trails and analyses of water and soil samples), asking them to evaluate it.

In the end 77 scientists reported back, and the results were not terribly surprising. Ninety-eight point seven percent (76 out of 77) of the scientists said they had encountered no evidence of a secret large-scale atmospheric program, or SLAP. Everything they saw on the conspiracy websites showed that what they were seeing was the natural consequence of airplanes flying around all on their own without government nefariousness.

Of course, the first thing you’ll notice is the one scientists who dissented. In that case, it’s hardly a smoking gun:

The one participant who answered yes said the evidence s/he had come across was “high levels of atm[ospheric] barium in a remote area with standard ‘low’ soil barium.”

In other words, they found some unusually high amounts of barium, which hardly supports the idea of wide-spread cover-ups of mind control techniques—and it sounds like the scientist in question was simply saying he or she can’t rule SLAP out, which is a far different thing than saying it’s real. When I can’t find my keys in the morning I can’t rule out that dinosaur ghosts hid them from me. It just seems a tad unlikely.

The research is actually rather interesting, and I encourage you to read it. But as the authors note, it won’t make a dent in the conspiracy theories. The first thing you’ll find out when you deal with people like that is that any evidence against them is part of the cover-up. This is what I call a philosophical cul-de-sac; they’ve removed themselves from any possible evidence and criticism, and at that point I’ve learned to walk away. At least to walk away from them specifically; in some cases it’s worth pursuing the discussion with the public because they’re liable to hear about it, and a place to find actual facts and debunking is a handy thing to make available.

Don't panic
Don't push the button, Frank.

Shutterstock/Shay Yacobinski

So I’m glad these scientists went to the effort, even though it may seem silly. Conspiracy theorists usually don’t make a big splash in real life, but if they get the ear of a politician, time, money, and effort can indeed be wasted, sometimes on a big scale. Given how anti-science so many members of Congress can be, I don’t think there’s any idea too silly for them to not take seriously.

If Congress critters think the Earth is cooling, that it’s only 6,000 years old, that vaccines are dangerous, and that the existence of snow disproves global warming, then chemtrails don’t seem like that much of a stretch.

Aug. 14 2016 9:00 AM

NASA Video Shows Meteor Shower … From Above!

Late last week marked the peak of the annual Perseid meteor shower, generally one of the most dependable shooting star shows of the year. You can usually spot about a meteor per minute streaking across the sky, leaving behind a momentary trail of vaporized rock that fades rapidly as it cools in the upper atmosphere.

Meteors burn up about 90 to 100 kilometers above the Earth’s surface. So what happens if you happen to be 400 kilometers up, orbiting the Earth? What would it look like if you were looking down, toward the Earth, during a meteor shower?

That video was made on Wednesday using a camera on the International Space Station, specifically designed to look for meteors from above.

Did you see the two meteors in the clip? One happens at six seconds in, the other at 16 (the bright flash at the start of the video is lightning in a storm). It looks like they’re right over the surface, but perspective distorts that; they’re way up high.

Here’s a funny thing, too: At best only one of those meteors was from the Perseids! The meteors in a shower all appear to come from one part of the sky, as the Earth plows through the debris. It’s like driving through a rain storm, where the drops hit your front windshield because that’s facing into your direction of travel.

But the two meteors in the video are traveling at right angles to each other (one moves up, the other to the right). From the height of ISS all Perseids should travel in more or less the same direction, so at least one of those was not a Perseid! It’s possible neither were, but I can’t be sure without knowing the direction of the ISS movement, the exact time of the shot, and information like that. Still, the video is very cool.

It was made as part of a joint venture between the U.S. Southwest Research Institute and Japan’s Planetary Exploration Research Center, part of a project called Meteor Composition Determination. Besides taking video like the one above it also employs a special type of spectroscopic device called a transmission diffraction grating. This acts like a prism, breaking up the light of the meteors into colors. The resulting spectrum reveals the composition of the meteoroid (the solid bit of debris that burns up); every element has a unique pattern of colored light it emits as it glows. Since these meteors come from comets, it’s a way of studying comets right here on (well, above) Earth.

I went out with friends to see the shower on Friday night. We didn’t see too many over the two hours we were there; maybe a dozen or so. To be honest, being north of Los Angeles I’m surprised it was dark enough to see any, and the Moon was up too). But in this case it was just as much fun to hang out with friends as it was to watch the show. Meteor showers are wonderful, and I urge you to go out and watch one sometime. The next good one is probably the Leonids in November, and then the Geminids in December. Mark your calendars!

Aug. 13 2016 9:00 AM

When the Sun Never Sets

One of the funny things about living on a big spinning ball of rock and metal in space is that what you see depends on where you are.

Where I live, in Colorado, the Sun rises every day, makes an arc in the sky, then sets some time later. The same is probably true for you, too. What’s really happening is that we’re affixed to that spinning ball, and as it sweeps us around we move in a tilted circle, sometimes on the side of the Earth facing the Sun, sometimes facing away, but always in motion.

That view changes dramatically with latitude. If you go far enough north, then after the (northern) Vernal Equinox in March, the Sun never sets. The Earth’s North Pole is tipped toward the Sun, and even though it spins some parts of the Earth are in constant daylight, and remain so for months at a time.

I’ve seen time-lapse videos taken from cameras fixed to a tripod, showing the Sun moving around in a circle (or sweeping back and forth over the horizon). But what does it look like if, instead, the camera tracked the Sun’s path along the horizon as it moved?

Why, it would look like this.

That video, created by Witek Kaszkin, is pretty amazing. It sweeps along, moving horizontally as the Sun does too, keeping the horizon in the same place. As the Earth spins, the Sun bobs up and down over the course of a day, and also moves all the way around the sky. It’s a peculiar way of showing the motions, but I like how it shows the Sun’s change in altitude over the day, rising and sinking, but never setting …  it almost does, but in reality it just gets behind some tall, distant mountains.

The video was taken in April 2015, not long after the equinox, so the Sun does dip low to the ground, though never reaching it. The camera was at 77° north latitude, near the Polish Polar Station Hornsund at Svalbard, a few hundred kilometers east of Greenland (Kaszkin has another video from the same location showing a solar eclipse, which is really cool, and there’s a video of polar bears visiting the station, too).

If the Sun’s motion in the video confuses you, then I suggest reading a post I wrote about why the Sun never sets on the North Pole in summer, which has a more detailed explanation (and another cool video as well). The fun part of all this is how the motions and positions are all relative; the Earth is tipped, or the Sun is. The camera sees the Sun moving, or the Earth moving. The Sun bobs up and down, or really you do as you spin around the Earth.

What you see depends on your point of view, and if you change the way you see it you change what you see.

If there’s a life lesson to be had there, feel free to take it.

Tip o’ the axis to Greg Owen.

Aug. 12 2016 9:00 AM

ORION. Holy Wow, Orion.

At a distance of 1,300 light years —just 13,000 trillion kilometers, which is close on a galactic scale—the Orion Nebula is one of the most magnificent objects in the sky. It’s so luminous that you can see it by eye even in mildly light polluted areas, and when you use binoculars you can tell it’s not a star, but something fuzzy and big, hinting at its true nature.

That nature comes into clarity when the nebula is photographed using a telescope. That reveals it to be an immense cloud of gas and dust, light years across, a factory for creating stars, colorful and spectacular.

But why describe it when I can show you? Behold!

Aug. 11 2016 9:00 AM

A Chance to See Moons Around the Exoplanet Beta Pic B in 2017

I don’t usually write about observations that haven’t been done yet, but this is so interesting I wanted to tell y’all about it. Next year, due to a quirk of geometry, it’ll be possible for astronomers to search for moons or other debris around the exoplanet Beta Pictoris b. They won’t be able to see the planet itself, but if there’s stuff around, that might be detectable.

The star in question is Beta Pictoris, which is about 60 light-years away (that’s relatively close). It’s more massive, hotter, and brighter than the Sun. It’s also considerably younger: It’s about 25 million years old, while our star is more than 4.5 billion years in age.

Beta Pic disk
The disk around Beta Pictoris is visible in this Hubble image. The starlight was blocked by a mask (black circle) to prevent it from flooding the image and making the disk impossibe to see.

NASA,ESA, D. Golimowski (Johns Hopkins University), D. Ardila (IPAC), J. Krist (JPL), M. Clampin (GSFC), H. Ford (JHU), and G. Illingworth (UCO/Lick) and the ACS Science Team

In 1983 astronomers found that Beta Pic was putting out more infrared light than expected, and detailed observations revealed it was surrounded by a disk of warm dust and debris, the material left over from the formation of the star (I remember doing a homework problem in grad school about the excess IR light from the star, using it to calculate the mass of the disk). As it happens, we see this disk nearly edge-on.

Then things got even more exciting: In 2003, observations using the Very Large Telescope directly imaged an exoplanet orbiting Beta Pic!

Called Beta Pictoris b, it has about seven times the mass of Jupiter, and orbits the star roughly every 20 years. In fact, its motion around the star can be seen; observations made in 2009 and 2010 show it on the other side of the star from where it was in 2003!

Beta Pic b
The exoplanet Beta Pictoris b is one of a few that has been directly imaged. It was seen in 2003 (upper left), again in 2009 (upper right), and again in 2010 (bottom). The size of the orbit of Saturn is shown for comparison.

M. Bonnefoy et al., published in Astronomy & Astrophysics, 2011, vol. 528, L15

Getting the exact orbit of the planet is difficult because it’s hard to get accurate enough observations to really pin it down. However, using new techniques, a team of astronomers looked at data from the massive Gemini telescope to get amazingly accurate positional data from the planet. What they found was good news and bad news.

The bad news is that the planet’s orbit is almost certainly not edge-on as seen from Earth (that would need a tilt of 90°, but the tilt they found is 88.8°—close but no cigar). That means the planet doesn’t actually transit its star, passing directly across the star’s face as seen from Earth. That would be nice, because that sort of observation can be used to get the planet’s size.

But not all is lost. The good news is that the planet gets very close to transiting the star, close enough that its Hill sphere will actually pass in front of it.

What’s a Hill sphere? Why, I’m glad I asked.

Gravity depends in part on how far you are from a massive object. As you move farther away, it weakens. If that object is a planet, and it orbits a star, at some distance from the planet the star’s gravity has more influence on an object in space than the planet’s gravity. If you’re closer to the planet the planet’s gravity dominates, and it can hold on to orbiting objects. That defines a spherical region around the planet, called the Hill sphere.

The size of the sphere depends on the mass of the planet, the mass of the star, and the distance between them. For example, the Earth’s Hill sphere reaches out to about 1.5 million kilometers. The Moon, orbiting 380,000 km away, is well inside that, so its motion is mostly influenced by the Earth (some people like to say the Moon orbits the Sun more than it does the Earth, but those people are wrong). Weirdly, Pluto’s Hill sphere is much larger than Earth’s, but that’s because it’s so far from the Sun that an object can orbit Pluto from farther away and still be heavily influenced by it.

The Hill sphere for Beta Pic b is more than 160 million kilometers in radius, which is pretty large. That means it can hold on to moons or some of that leftover debris out to that distance. Although the planet itself won’t transit the star, it turns out that this region will, starting in April 2017 and ending in January 2018. The planet’s closest approach to the star will be in August, which is when the transit could allow astronomers to probe material closest to the planet.

I won’t mince words: This is really cool! The astronomers suggest a campaign to observe the star during these times, though they note that the first half of the Hill sphere transit won’t be easily visible to ground-based telescopes because it will be near the Sun in the sky (though space-based ‘scopes should be able to take a peek). But the second half of the transit should be visible to observatories in the Southern Hemisphere.

Hopefully constant monitoring will be done. There’s no guarantee anything will be seen, but if a large moon does happen to pass in front of the star, this would be the first such exomoon ever seen (assuming none is found between now and then orbiting some other exoplanet). That’s a very big deal indeed. Moons orbiting planets gives us a chance to determine the mass of the planet, for one thing.

And for another, we’ll be detecting a moon orbiting a planet that in turn is orbiting an alien star!

That is just simply cool. But it’s also premature. We’ll have to wait and see, and keep our astronomical eyes open. This is a chance that won’t come back until Beta Pic b circles its star once again … in just another 20 years or so.

Tip o’ the dew shield to Jason Wang on the Exoplanet Imaging Group on Facebook.

Aug. 10 2016 9:00 AM

I Still Still Don’t Think It’s Aliens, but Tabby’s Star Keeps Getting Weirder

Just when you think Tabby’s Star can’t get any weirder, it goes and does.

You know this star: It undergoes very odd dips in brightness that have defied explanation. The star, formally called KIC 8462852 (but nicknamed Tabby’s Star after Tabetha Boyajian, the astronomer who led the team investigating it), has been observed by the Kepler spacecraft for some time now. Kepler looks for dips in brightness in stars indicating the presence of a planet orbiting it; the planet blocks a tiny bit of star light, and that drop in brightness can be detected.

But Tabby’s Star isn’t behaving itself. Instead of a smooth dip and subsequent rise in brightness indicating a planet, it suffers nonperiodic, asymmetric, and very deep dips in brightness. This is not at all what you expect from a planet. Ideas including shattered asteroids and swarms of comets explain some but not all of the dips.

After a while people began to wonder: What if advanced aliens were building huge megastructures around the star, in order to capture its light to power their civilization? I know, that’s a bit far-fetched, but it actually fits the data pretty well. No scientist really thinks that’s the case—it’s a reach, and no signals from aliens have been found—but nothing else works, either. It’s baffling.

Then an announcement was made that over the past century or more the star has been fading at an unprecedented rate. This finding was immediately called into question, though, and the issue of fading remained unresolved.

But now a new study, using data from Kepler itself, shows that Tabby’s Star really is fading, and at quite a clip: Over three years of observation it faded by nearly 1 percent, then took a sudden nosedive, fading by two percent in the next 200 days.

Tabby's star fading
Data from Kepler show Tabby's Star faded by 3 percent over about four years. The symbols represent various Kepler observations, and the gray line is a fit to other observations of the star.

Montet and Simon

I know, that doesn’t sound like much, but remember this is an entire star, a mighty source of energy. Stars like this one just don’t do that! What’s causing it?

The astronomers first looked at the data to make sure the fading was real, and after careful investigation concluded it is. It’s not some instrumental effect from Kepler itself, but instead is something happening on, at, or near the star.

They looked for other factors, like stars around it changing brightness, but don’t see anything amiss that might throw off the data. They looked at quite a few stars around Tabby’s, and only saw a handful that exhibit similar fading, but none with that sudden 2 percent drop.

Whatever that star is doing, it’s actually doing it.

So what could it be? It’s not a planet; it would have to be far larger (0.15 times the size of the star itself!) than any planet could be to make such a large dip, and the slow change would mean it was implausibly far from the star. A cloud of material might do the trick, slowly passing in front of the star and blocking its light, but that doesn’t explain the sharp dips, either.

The researchers find that a recent collision of asteroids or comets might account for almost everything seen; the big dips would be from clouds of material, and the smaller rapid dips from more solid bodies. But that doesn’t explain the centurylong dip, or the fading seen by Kepler (I’ll note the recent fading is consistent broadly with the much longer fading, but doesn’t necessarily prove it’s real).

Nothing explains everything we see. It’s a mystery.

Clearly, more observations are needed. A cloud of dust could redden the star, in much the same way that atmospheric haze on Earth makes the setting Sun look redder, so a change in the star’s color would be interesting. The astronomers also suggest looking for planets farther out from the star, perhaps a few hundred million kilometers from it. The gravity from a planet like that could, in theory, gravitationally align a disk of material around the star (think of it as a thick, dusty asteroid belt) that could explain some of the features.

Belt of Dust
A belt of debris might explain some of the observations. But not all.

Artist drawing by NASA/JPL-Caltech/T. Pyle (SSC)

Could that be what’s doing all this? Maaaaaaybe. There are still a few ideas tossed around that can explain Tabby’s Star’s behavior, but all are maddeningly, tantalizingly difficult to ascertain.

Mind you, I’m still not saying aliens. I really and quite seriously don’t think that’s it. It’s more likely we’re seeing a combination of effects doing this; a cloud of material sliding in front of the star, dimming it slowly, with thicker clumps causing the sharper fading. But even that doesn’t explain all the data.

The only thing we know for sure is that we haven’t ever seen anything like this before, and that we are seeing is really, really weird.

And weird is good! Scientists love mysteries, especially the distinctly odd ones. This is tremendously fun science, with more questions than answers. But with more observations and more clever analyses, I hope that will reverse. Even if it’s not a technologically advanced civilization, I want to know what is going on!

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.

Sheesh.

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.

READ MORE STORIES