I haven’t written about our laser-eyed nuclear-powered red-planet roaming friend in a while. But the Curiosity rover recently celebrated its second year on Mars (which is really just over one Martian year on Mars). It’s still rolling along—literally—heading for its ultimate target: Aeolis Mons, aka Mount Sharp, the 5.5 kilometer-high peak in the center of Gale Crater, Curiosity's landing site.
Of course, it’s finding a lot of fun souvenirs along the way, and doing amazing science. Caltech put together a nice video as a retrospective of the past two years, as well as a look forward to what it will do soon.
It’s narrated by a couple of folks who might sound familiar, too. I won’t give it away (but it’s on the YouTube page show notes).
Nice. I have a public lecture I give about Curiosity, and it’s one of my favorites to give of all time. The human effort that went into building, launching, landing, and using this machine is nothing short of Herculean, and still it marches on. It’s a triumph, and I quite seriously choke up during the talk every time. I’m so proud of what we can do.
Congratulations to everyone who is involved with Curiosity and also to those who are building the 2020 rover too. Whenever I see Mars in the night sky, I see it as more than just a red dot: It’s an entire world, and one we’re just now starting to explore.
Did I Say 30 Billion Tons of CO2 a Year? I Meant 40.
Every now and again a global warming denier will say that humans aren’t putting much carbon dioxide into the air, and it’s less than a lot of natural sources. I’ve pointed out that in fact, humans throw about 30 billion tons of it into the atmosphere every year, 100 times as much as volcanoes do. I got that number from a paper published a few years back.
Well, I just found out that paper is out of date. Guesss what the more accurate, current number for the human-made CO2 pollution put into the air every year is?
40 billion tons.
Yeah. 40. As in billions of tons. 40.
That number comes from an assessment made by Le Quéré et al. in a paper measuring the total carbon budget for the planet in 2013. I found out about this new, updated number when I wrote about the launch of NASA’s Orbiting Carbon Observatory, or OCO. I mentioned the older number in the post, and got an email from David Crisp, OCO’s science team leader (!) correcting me.
It’s almost impossible to grasp what 40 billion tons means. A cubic kilometer of water weighs a billion tons, but it’s hard to imagine a cube 3.5 kilometers (2.2 miles) on a side—the equivalent amount of water weighing 40 billion tons. The largest class of aircraft carrier weighs about 100,000 tons, but picturing 400,000 of them still strains the imagination (not to mention vaporizing them into the air every year).
It’s a vast amount.
Funny, though, it’s small compared with the total mass of the Earth’s atmosphere, which is a staggering 5 x 1015—5 quadrillion— tons! By mass, this extra CO2 is only about 0.0008 percent of the Earth’s total air.
But it adds up. By volume, CO2 is about 400 parts per million (ppm) of the atmosphere, or about 0.04 percent. How much are we adding? Looking at the Keeling Curve, which measures the concentration of CO2 in the air, we’ve added about 20 ppm in the 10 years from 2000 to 2010—that’s 2 ppm per year.
So, that 40 billion tons of extra carbon dioxide we dump into the air every year is accumulating at a rate of 2 parts per million when you look at the entire atmosphere.
That sounds pretty small. But is it?
I wish. For some things, it doesn't take a lot to make a huge difference. As doctors will tell you, dose makes the poison. Four hundred ppm sounds like a small amount, but this concentration of carbon dioxide in our atmosphere is enough to raise the average temperature of the Earth significantly … and we’re putting more of it into the air every year.
Forty billion tons worth. That’s why the planet is heating up. That’s why the climate is changing. That’s most likely why we’re seeing more extreme weather, hurricanes getting stronger, droughts drier, forest fires more intense.
This is our fault, and it’s also most definitely our problem. There is hope … but we need to get our heads out of the sand together and take action. Now.
Venus and Jupiter, Together
Over the past few mornings, the fourth and fifth brightest objects in the sky have been getting cozy. Venus and Jupiter are very close together just before sunrise, and have made for some lovely photo ops.
The planets orbit the Sun in roughly the same plane; if you looked at the solar system from the side it would look fairly flat. To us on Earth, in that plane, the planets all stick more-or-less to a line that circles the sky, which we call the ecliptic. It’s not perfect; some planets have orbits that are slightly tilted, so it’s not exactly beads on a string. But sometimes they do pass pretty close together, and it makes for a striking sight.
Jupiter is currently on the other side of the Sun from us, more than 900 million kilometers (almost 600 million miles) away. Venus is also on the other side of the Sun from us, but much closer: 240 million km (150 million miles) away. Jupiter is a far bigger planet, but Venus is closer and more reflective, so it appears the brighter of the two.
The photo at the top of this post is a part of a larger portrait of the pair as they appeared on the morning of Aug. 18, 2014. It was taken by Jerry Lodriguss in New Jersey, from a cranberry bog (which explains the light mist covering the ground). He also took the photo below:
You can see two moons of Jupiter (Io and Europa) just above it and to the right, as well as an airplane zooming by to the left. Make sure to take a look at a time exposure Lodriguss took of the two rising; they appear as long, colored streaks moving up from the horizon
Due to the complicated dance of orbits of the two planets (and our own Earth, changing the perspective on the pair), Venus is moving toward the Sun in the sky, rising later every morning, while Jupiter is slowly pulling away form the Sun, rising a bit earlier. The two are still close together for the next few days, so if you’re an early riser it’s worth getting up just before sunrise to look for them. Simply look east, but you’ll need a good view of the horizon; they’re not very high up.
Oh—so if they’re the 4th and 5th brightest objects in the sky, what are the first three? The Sun, of course, and the Moon … and No. 3 is the International Space Station, though to be fair it is only sometimes brighter than Venus. No matter; while the ISS is fun to watch, there is something about looking at a planet in the sky and knowing it’s an entire world, hanging there for us to see. It’s very much worth an early morning to catch a glimpse.
In the Northern Hemisphere it’s summer. That means warm sunshine, gentle breezes, lake water evaporating and forming lovely, puffy clouds …
Oh. Did you think I meant here? No, no, no. I meant Titan!
Titan is Saturn’s largest moon, and it’s actually bigger than the planet Mercury. It has a thick atmosphere of nitrogen, with a surface pressure half again as much as Earth at sea level. It’s cold there, about -180° C (-290° F), cold enough that water ice is hard as rock, and methane is a liquid on the surface.
In fact, methane there is like water here: It can be a liquid or a gas, depending on the local conditions. One of the Cassini mission’s biggest surprises, and totally cool discoveries, is the presence of lakes of liquid methane near the moon’s north pole. Lots of channels line the surface, too, indicating that methane must evaporate from the lakes, condense as clouds, then rain out, running along the channels.
And now, with the onset of northern summer, Cassini has taken images of clouds forming over a lake named Ligeia Mare (Ligeia was one of the mythological sirens), and these images form one of the most amazing animations I’ve seen from the outer solar system:
Wow. The lakes are the dark regions, and the clouds form over the western edge of Ligeia Mare, blowing east (right). The winds are moving at about 12-16 kph (7-10 mph); breezy but not too bad. The wind chill is like minus a bazillion, but if you’re Titanian I’m sure it would feel refreshing.
These clouds have been anticipated by planetary scientists for some time, and have frankly been overdue. In late 2010, a huge storm swept over the equatorial region of Titan, and for some reason cloud formation has been suppressed since then. These clouds may mark the return of normal weather on the ridiculously huge moon.
It’s really odd to think of a moon having weather, especially one well over a billion kilometers from the Sun, where the temperature would nearly liquefy the oxygen out of our own air. But there you go. And it’s not just weather, but really in many ways it’s quite Earth-like. Methane lakes, a methane cycle, lots of organic compounds lying around … it’s no wonder a lot of scientists take the idea of exobiology seriously on Titan. Cassini has sent us a lot of amazing data, and a lot of tantalizing clues. I’d love to send a dedicated probe there, something that could land, move around, taste the local flavors. A few years ago it would’ve been the last place I would’ve thought to look for extant life, but nowadays it’s near the top of everyone’s list.
The Fiery Final Descent of a Spaceship
How Do You Weigh a Helium Balloon?
My friend Jenny Lawson—aka The Bloggess—is weird.
This isn’t casting any aspersions! She would be the first one to admit it. In fact, she does, constantly, on her blog. If you read her book, Let's Pretend This Never Happened, you'll find this assessment is ironclad.
For further evidence: Just the other day, she was in a conversation with her husband, Victor.* She asked him, “What weighs more, five pounds of helium, or five pounds of cheese?” She wrote up the exchange on her blog, and tweeted a link it. I laughed when I saw it, and immediately replied:
@TheBloggess I actually know the scientific answer to this.— Phil Plait (@BadAstronomer) August 10, 2014
@BadAstronomer It has to do with which type of cheese, doesn't it? I'm awful with math.— TheBloggess (@TheBloggess) August 10, 2014
To which I made the obvious rejoinder:
@TheBloggess Yes! Swiss cheese weighs less. The holes, you know.— Phil Plait (@BadAstronomer) August 10, 2014
It only occurred to me recently to wonder about filling the Swiss cheese holes with helium.
But in reality, I do know the answer. This question is an old variation on the riddle, “What weighs more, a pound of lead or a pound of feathers?” The answer is neither: They both weigh a pound. But I remember hearing this riddle when I was but a wee lad, and being momentarily baffled. We humans sometimes confuse weight and density; lead is very dense, but a pound’s a pound the world around. A pound of feathers would take up a lot more space, but it would still weigh a pound.
But in the case of Jenny’s question, we get even more confused. After all, helium floats! If you had a balloon full of helium, and tried to weigh it on a scale, it would float away. If you could somehow tie it to the scale—and you had a scale with the decidedly odd characteristic that it could measure numbers less than zero—it would say the balloon has negative weight!
But that’s not really the case. Here’s the answer: A balloon filled with five pounds of helium would weigh exactly the same as a five pound block of cheese.
How can this be? Ah, let me explain.
What we think of as weight is really a force—the acceleration due to gravity acting on our mass. Mass is a property of matter that is independent of weight. I have a mass of about 80 kilograms, and I would have this same mass on the Earth, the Moon, or the surface of a neutron star. It’s basically telling you how much matter makes up me.
On Earth, with its one Earth gravity, I feel that mass as a weight. The Earth pulls down on me, and if I step on a scale it says I have a weight of about 175 pounds. If I were on the Moon, with 1/6th the Earth’s gravity, I’d weigh just shy of 30 pounds. My mass is still the same (80 kilos), but there’s less gravity pulling on me. I weigh less!
All matter has mass. Even helium. So let’s say I have some amount of helium—borrowing from Jenny, call it 2.3 kilos. On Earth, that would weigh five pounds. Earth’s gravity still pulls on that helium, and given that mass, the force works out to be five pounds.
But the difference between helium and cheese is that helium is very low density, lower than the air around it. That makes it buoyant. Buoyancy is a force too, like gravity, but it works in the opposite direction: It pushes things up. It only makes objects float if they are less dense than their surroundings, like a boat on water, or a helium balloon in air.†
Buoyancy works due to displacement. If I take a chunk of iron a centimeter on a side (the size of a six-sided die) and drop it in water, it sinks. The amount of water it displaces (pushes aside due to its volume) weighs less than the iron does, so down the iron goes.
But if I spread the iron out, make it bowl-shaped, it can actually displace a lot more water. If it pushes out the amount of water equivalent to its own weight, then it’ll float! The water it pushes out wants to flow back under it, and that is a force pushing up on the iron. When the water displaced weighs the same as the iron, the two forces balance. The iron floats. That’s how big steel ships float; they’re spread out, and they displace their own weight in water.
In the case of a balloon, the helium inside the balloon weighs less than the same volume of air the balloon displaces. This air outside pushes on the balloon, and up it goes!
So a helium balloon has two opposing forces acting on it: gravity pulling it down, and buoyancy pushing it up. Buoyancy wins, so you can’t really weigh a balloon, even though it does have weight.
Weird, eh? Think of it this way: If you could put a balloon with five pounds of helium in it in a vacuum chamber, then there’d be no buoyancy force pushing it up. Only gravity acts on it, so if it sat on a scale it would register as five pounds!
Tadaa! See? A five pound balloon weighs the same as a five pound piece of cheese. It would just be less tasty.
Still, I started thinking … how would you weigh a helium balloon? How could you know it weighs five pounds if you can’t weigh it on a scale?
I can think of a few ways. (Note: For all these methods, I will ignore the weight of the balloon material itself, which is hopefully small compared with five pounds.)
For one, you could look up the density of helium in a balloon, then multiply it by the volume you’d need so that it weighs five pounds. In air, helium has a density of 0.2 kilograms/cubic meter, so you’d need about 11 cubic meters of helium to weigh five pounds, which would be a balloon about three meters across. That’s a lot of helium. In reality it would be a bit smaller, since the pressure inside a balloon is higher than the air around it, but eh. Close enough.
I thought of another way, which is to mount a scale upside down on the ceiling and let the balloon rest against it. But then I realize that won’t work; the force of buoyancy pushing it up is actually greater than its weight, that’s why it keeps floating up when you let it go outside (which sometimes leads to another inexorable force of nature, the force of a child crying).
But then I realized you could let a balloon go outside. It’ll float up, getting higher and higher, where the air is thinner (less dense) until eventually the weight of the air displaced by the balloon is equal to the weight of the helium in the balloon. At that point it will stop rising. You can then determine the altitude of the balloon (perhaps using a few spotters with known locations, and a bit of trig as they measure the balloon’s angle in the sky). Then look up the known density of air at that height, and the volume of the balloon (oops: measure that before you let it go) to get the weight of the air displaced. That’s equal to the weight of the helium! Well, more or less; the balloon will expand as it rises, but in principle you could find the helium weight this way. It’ll also be very high up, probably a few miles, but in principle this would work.
Still, that’s pretty complicated. A much easier and practical way is to buy a big tank of helium. Set it on a scale and weigh it. Now grab a balloon (a big one) and start filling it. When the scale says the tank has lost five pounds, you’re done! Note: My wife thought of this one, and then scolded me for making this too complicated. I suspect my own marriage is much like Jenny’s.
There are other ways, too, but they get a bit impractical (like cooling the helium until it’s a liquid, no longer buoyant in air, and then putting it on a scale; The problem with this is helium liquefies at 4 Kelvins, or -269° Celsius, which is -452° Fahrenheit. That’s a tad pricey and difficult of a procedure, as well as incredibly dangerous to do at home).
But the point is, it’s entirely possible to have a five pound balloon of helium. Mind you, it’ll lift a lot more than five pounds; a balloon that size can lift about 25 pounds. You could tie the cheese to it and it would still float away! That’s a waste of a balloon, and cheese. I don’t recommend this either.
@TheBloggess Actually, I may write a post on this. It’s actually fun science. Which is all science.— Phil Plait (@BadAstronomer) August 10, 2014
So there you go, Jenny. I told you I knew the answer to this, because science. In fact, I even tweeted it:
*I sometimes wonder if she makes these conversations up for the sake of humor, but then—having met them both—I rid myself of that outlandish notion.
†Update, Aug. 18, 2014 at 14:30 UTC: I originally said buoyancy only works on objects less dense than their surroundings, which was somewhat sloppy of me. It works on any object surrounded by a less dense medium, too; it's just that in that case the object won't float. I tightened up the language here to clear that up.
No, a Huge Asteroid Is NOT “Set to Wipe Out Life on Earth in 2880”
What is it about crappy reporting and asteroids?
The culprit this time is the UK’s Telegraph. In its search to become ever more Daily Mail-ian, it ran an article about an asteroid called 1950 DA with this headline:
Huge asteroid set to wipe out life on Earth - in 2880
Along with a not-so-subtle (but cool) piece of artwork of a gigantic asteroid impacting the Earth:
Yeah. The only problem with this: It’s very, very unlikely the asteroid will whack us in 2880, so at best that headline is hugely misleading. And this ain’t “at best.” The real situation will take a moment to explain, but as usual, really cool science is involved.
The Asteroid, and Its Really Cool Science
1950 DA has been in the news lately because a team of scientists examined how rapidly it rotates and found something remarkable: The asteroid spins so quickly that it should fly apart! You might think of asteroids as solid, monolithic chunks of rock, but we know that some are “rubble piles,” collections of smaller rocks held together presumably by their own gravity. They probably started out solid, but repeated collisions over the eons have riddled them with cracks, so they are more like gigantic bags of shattered rock.
1950 DA is one of these rubble piles. It’s also a rapid rotator; one “day” on the asteroid is only about two hours long. It’s about 1.3 kilometers across, which means that if you were standing on its equator, the pull of gravity down, holding you to the surface, would be slightly less than the centrifugal force outward. You’d be launched into space!
That would be odd enough on a solid rock, but since 1950 DA isn’t solid, that means it should fly apart. It doesn’t, which means there must be some other force holding it together. The scientists speculate over what that force might be, suggesting the van der Waals force, a complicated effect that can be thought of as an electrostatic charge between molecules (though that’s oversimplifying it). This idea has been around for a few years, but this is the first time it’s been studied in detail specifically for 1950 DA.
Learning about asteroids is fascinating and scientifically important, of course, but there are practical considerations as well: If we find an asteroid that might someday hit the Earth, we’ll have to do something to prevent that. One idea is to hit a dangerous asteroid with a space probe with enough force to alter the asteroid’s orbit. The physical characteristics of the rock will be a big factor in that; if it’s metal, rock, or a rubble pile it will react differently to the impact. The more rocks like 1950 DA we study, the better.
But of course, this is isn’t where the Telegraph went.
The Headline, and Its Really Not Cool Science
As it happens, 1950 DA is what’s called a “near-Earth asteroid,” because its orbit sometimes brings it relatively close to Earth. I’ll note that I mean close on a cosmic scale. Looking over the next few decades, a typical pass is tens of millions of kilometers away, with some as close as 5 million kilometers—which is still more than 10 times farther away than the Moon! Still, that’s in our neighborhood, which is one of the reasons this asteroid is studied so well. It gets close enough that we can get a decent look at it when it passes.
Can it impact the Earth? Yes, kind of. Right now, the orbit of the asteroid doesn’t bring it close enough to hit us. But there are forces acting on asteroids over time that subtly change their orbits; one of them is called the YORP effect, a weak force that arises due to the way the asteroid spins and radiates away heat. The infrared photons it emits when it’s warm carry away a teeny tiny bit of momentum, and they act pretty much like an incredibly low-thrust rocket. Over many years, this can change both the rotation of the asteroid as well as the shape of its orbit.
Predicting an asteroid’s position over the years is a dicey proposition at best. Small uncertainties in its measured position propagate into bigger errors down the line, so the farther into the future you try to predict where the asteroid will be, the fuzzier that position gets. As I’ve written before:
Think of it this way. Imagine you’re an outfielder in a baseball game. You see the pitcher throw the ball, and the batter swings. It’s a hit! But one-tenth of a second after the batter makes contact, you close your eyes.
Now, based on the fraction of a second you saw the ball move, can you catch it?
I would be willing to bet a lot of money you won’t. You weren’t able to watch the ball long enough to get a good fix on its direction, its speed, its position. It could land next to you, or it could fall 40 meters away, or it could be knocked right out of the park.
1950 DA is a bit of an exception, though. We have observations going back many decades (1950 is the year it was discovered), and we also have radar observations of it made in 2001, and those provide very accurate position measurements. This allows the orbit of 1950 DA to be determined farther into the future than most asteroids. Last year, another team of scientists looked into this. They accounted for a lot of small effects on the asteroid, including the YORP thrust, the gravity of the planets, the gravity of other asteroids, and so on. They found that the probability of an impact in 2880 is about 2.48 x 10-4, which is about 1 in 4,000. That’s really small.
That’s one reason the Telegraph headline is so awful (note: They also use an old probability of 1 in 300 for an impact, too). The other is simply due to its hyperventilating fear-mongering, something I find very distasteful. To say the least.
I’m no fan of the Telegraph; their predilection for printing global warming denial is loathsome, and they dip their toe into other forms of pseudoscience as well. I’ll note this story was picked up uncritically by other venues like MSN UK (which added its own errors; saying the asteroid was discovered by the team of scientists I write about above) and the Daily News, too.
Shame on them. And, just to be clear:
Tip o’ the Whipple Shield to Christine Pulliam and David Bustard for pointing these articles out to me.
My Life as a Comic
Oh, I do get around.
And now, it so happens, I’ve had something of a run-in with Red Sonja, too. A little while back, Dynamite Entertainment bought the rights to Red Sonja, and it’s been re-imagined by my pal Gail Simone. I really like Gail, and what she’s done with the character. The inherent sexism in the character’s backstory has been essentially erased, and now she’s smart, bawdy, strong—both physically, morally, and in her depth of thought—and sees a world that can be better. And she’s willing to cut off the head of a demon or two to make sure it happens. Gail is an outspoken supporter of women's and LGBT rights, so this new take on Red Sonja is no surprise for me. I like it.
The new issue (#11) is a fun story, and I won’t give it away. But it’s worth picking up if only for a familiar character … and Gail says there’s more to come in #12. I will definitely be picking that one up, too.
*Correction, Aug. 16 at 16:00 UTC: ARG! I originally wrote that I was quoted in Ant Man, but it was in The All New Atom. That's my own silly fault: Gail wrote that issue as well, and when I was talking to her about it at a convention last year, I accidentally called it Ant Man. I was embarrassed by that! Now, somehow, the two have become conflated in my head, and apparently I am doomed to make that mistake over and again for the rest of my life. Sorry, Gail!
No, Google Moon Doesn’t Show an Alien Loitering on the Moon
This is Part N in what is apparently a never-ending series of articles that have a title that starts with “No, … .” You can find more in the related posts at the bottom of this post.
Update, Aug. 15, 2014 at 16:30 UTC: ARRRRG! I was soooo close. It turns out this object is actually a bit of dirt or debris that was in the lens of the camera that took it. This was in fact my first thought, but when I saw that the images used in Google Moon were from Clementine, I dismissed that idea, since the cameras used by space probes are very clean. What I didn't know (and didn't see in the Google Moon page) is that they also used Apollo images. The pictures in question were from a mapping camera on Apollo 15 (which is known to have had blemishes in its photos) and the link above explains the whole thing. I leave the blog post below intact so you can see my reasoning, but I also wanted to make sure you all see that I was right for mostly the right reasons, but in the end there was a critical piece of information I didn't have—what camera was used on what mission. My thanks to Mick West on Twitter for notifying me.
A video is making the rounds right now that doesn't-claim-but-still-kinda-claims there’s a picture of a figure standing on the Moon. Some sites use the word "alien."
First, here’s the video:
In the video, YouTube user wowforreeel shows this weird dark shape on the Moon. I made a screen grab of it, and you can see it at the top of this post. Note wowforreeel labels the upper left part of it “Man?” and the lower part “Shadow.”
Right away I can tell that’s wrong. Look at the crater to the left; see how the rim is lit on the upper left, and the lower right is in shadow? That means the sunlight is coming from the lower right, and shadows are cast to the upper left. If this object is real, it’s the part to the lower right, casting the shadow to the upper left. I can see why wowforreeel labeled it that way, though; the “shadow” looks like it’s following the contour of the lunar landscape, as a shadow would.
But it can’t be a shadow, as I pointed out, so that makes me immediately suspicious this figure isn’t real. I don’t think I have to make it particularly clear that I don’t think it’s an alien, or even an alien shadow. Nor is it a statue “thousands of feet high,” as one article doesn't-claim-but-still-kinda-claims.
In the video wowforreeel is using Google Moon, which itself uses data from the Navy’s old Clementine mission for lunar images from 1994. But I knew we have more recent images, so I went to the Lunar Reconnaissance Orbiter atlas of the Moon. Putting in the given coordinates (27°34'26.35"N 19°36'4.75"W), I quickly found far higher resolution imagery of that spot:
As you can see, nothing is there (note the image is rotated a bit relative to the Google Moon shot). Perhaps the alien got bored standing around since 1994 and walked off. Incidentally, the crater to the left in the Google Moon image is also in the LRO image (cut off at the bottom). It’s roughly 350 meters across—almost four times longer than a football field. The figure is only a little smaller, so if it’s an alien, it’s a tall one. I’ll note the surface around that location is undisturbed—no footprints, tracks, or markings of any kind except dinky craters. If there was something there 10 years ago, and it was removed before LRO got there and took a picture, you’d expect there to be some surface scuffling.
So, to my satisfaction, this establishes the object isn’t real. But then I wondered: Is this something in the Clementine images, or is it something in the way Google Moon stitched the images together?
To check, I went to the NASA Lunar Mapping and Modeling Portal, found the same area … and saw that this “figure” appears very close to where there’s an image discontinuity, where different images taken at different times are connected together to make the bigger map.
That makes me strongly suspect this is not in the original Clementine images but instead is an issue with the way the Google Moon software is stitching pictures together to make the map. I’ve seen that sort of thing before.
So: It’s not in the LRO images, it’s not in the original Clementine images, but it is right where two images are stuck together. That’s good enough for me.
What we’ve got here is a case of what’s called “anomaly hunting”—looking for things that don’t immediately make sense. If you look hard enough, especially in data you don’t fully understand or have experience with, you’ll always find something weird. But it’s a big jump from something weird to something paranormal. I’d say an infinite one.
No, a Nearby Supernova Won't Wipe Us Out
No, a Pole Shift Won't Cause Global Superstorms
No, Our Solar System Is NOT a “Vortex”
No, April 4, 2014, Is NOT “Zero G Day.” No.
No, We Are NOT in a Climate “Pause”
No, an Asteroid Is Not Going to Wipe Out All Life on Earth in 2041
No, the World Isn't Cooling
No, Asteroid 2003 QQ47 Is NOT Going to Hit the Earth Next Week
No, the Polar Vortex Does Not Disprove Global Warming
No, Global Warming Has NOT Stopped
No, That’s NOT an Artificial Light on Mars (but read the follow-up too, please)
The Faces of Ultraviolet
I spend a lot of time thinking about how narrowly we see the Universe. Our eyes perceive the narrowest slice of the electromagnetic spectrum, the huge range of flavor lights comes in. Radio waves, infrared, ultraviolet, X-rays, gamma rays—they make visible light, from blue to red, seem hopelessly parochial.
You don’t need to go far outside what the eye can detect to learn a lot about the world around you. Photographer Thomas Leveritt knew this and decided to find out for himself what he could see.
Using a special filter and camera setup, he went outside in Brooklyn, New York, and took video of people in ultraviolet, using a monitor so they could see themselves as well. The results are amazing, and, I must add, delightful:
The genius part here was giving people sunscreen. The camera detects UV from the Sun that’s reflected off people’s skin; the point of sunscreen is to absorb that UV so it doesn’t even reach the skin. Since no UV is reflected from sunscreen, it appears black in the video, even though in visible light it looks white. It looks like people are smearing crude oil on their faces, which is pretty funny.
Ultraviolet is slightly higher energy than the bluest light we can see. It comes in three varieties: UVA, UVB, and UVC. These go from longest wavelength (lowest energy) to shortest (highest energy). The Sun emits far more UVA than UVB, and not a lot of UVC. That’s good: UVC has enough energy to kill cells. What little the Sun emits is mostly absorbed by the Earth’s air and the ozone layer (which is why we launch space telescopes like Hubble into orbit; they get above Earth’s irritatingly UV-opaque air and can see the higher energy light coming from objects in the Universe).
UVB is absorbed by ozone as well, but some gets through. Some small amounts are beneficial, triggering vitamin D production in the skin. If you get too much, though, it causes sunburn, destroys vitamin A in the skin, and causes cancer.
UVA is less dangerous than UVB but still not great. Long-term exposure can indirectly lead to cancer (creating chemical compounds that are carcinogenic) and destroys collagens in the skin that “age” it.
I contacted Leveritt, and he informed me that he used an AstroDon UVenus filter and a camera with a CMOS detector. Looking that information over, I think he was detecting light around a wavelength of 330–380 nanometers, smack dab in the UVA range.
It’s fascinating to see how skin looks different there. Melanin, a pigment in the skin, absorbs ultraviolet light much more than visible, so in the video patches of melanin—freckles!—look very dark. Glass blocks UV light quite well, especially in modern eyeglasses which are coated with a layer specifically designed to protect our eyes from solar UV. In the video it’s obvious that works.
Interestingly, some people’s teeth are very reflective in UV, and others’ weren’t. Plaque, resins in fillings or crowns, food, and enamel all absorb different amounts and colors of UV, probably accounting for those differences, too.
All in all, pretty cool. I’ve seen lots of thermal infrared imagers at various fairs, science demos, and so on, but never a UV one. Part of the problem is a source; bright sunlight works so you can film outdoors, but UV lights and such are expensive. It would be fun to play with a setup like this, looking at different plants, animals, even the night sky. (Venus is a favorite for near-UV astrophotography, because it highlights the planet’s clouds.)
Leveritt is a gifted portrait photographer, and I’m glad he’s getting some attention for this. I suspect manufacturers of sunscreen will be lining up to talk to him once they see this video.
Tip o’ the sunscreen tube cap to Jennifer Ouellette.