Mars Is Going Through a Bit of a Dry Spell. How Do We Know? Rusty Meteorites.
I love meteorites. I have quite a few myself; while I’ve never found one on a hunt I’ve bought them from collectors. There’s a wealth of science in them; many are as old or even older than Earth, having formed in the early solar system. Others are from asteroids that got smacked by other asteroids, the impact sending out shrapnel that eventually impacted Earth.
Of course, other planets get hit by them too. We’ve seen asteroid (or comet) impacts on Jupiter… but we’ve also seen meteorites on Mars. In 2005 the rover Opportunity found a meteorite on Mars, the first time we’d ever seen one on another planet’s surface. Many more have been found since then.
It turns out that finding meteorites tells us more than just about them: They can be used to measure the environment in which they sit, too. A team of scientists used some Martian meteorites to do just that, and discovered something rather interesting: Mars has been very, very dry for the past several million years.
Now, we know Mars is dry. But there’s some evidence for moisture; for example, the Curiosity rover found daily and seasonal moisture exchange between the surface and the atmosphere.
Lots of meteorites contain iron. Some are mostly iron, like a peculiar looking one found by Curiosity just recently. Others are mostly rock (called stony meteorites), but even they are rich in iron. While out in space that iron is pristine, but once it lands on a planet like Mars, weathering can begin, including oxidation. Under water, for example, the iron in meteorites will rust. That can also happen if there’s moisture in the air, too.
Combining all this, the scientists looked at several meteorites found by rovers on Mars, including the chemical analysis done by the rovers (Opportunity has a spectrometer, an instrument that can determine the chemical composition of specimens). They examined the data and found that the meteorites contained oxidized iron — most likely due to Martian weathering.
They also were able to make various assumptions about the ages of the meteorites; for example some are near a crater that has been dated at 50 million years old. That’s an upper limit to their age; they could have been from that impactor, or they may have fallen later. Others were dated using similar methods.
What the scientists found is that the rate of oxidation is at best the same as what it would be at some of the driest places on Earth (like Antarctica), and could be far slower than that, perhaps as much as ten thousands times slower.
What this means is that in recent times, at least at these locations, Mars is dry, dry, dry. Perhaps at other spots the conditions are wetter, but the resting places for the meteorites are positively desiccated. As it happens, Mars may be in an interglacial period, an epoch of time when it’s a tad warmer than usual, with drier conditions at the equator. These meteorites support that idea.
In some sense that’s good news; it means that interpreting the geology at these places is easier, since weathering is low. But it also means that finding extant life on Mars may be harder. Looking at higher latitudes where we know there's ice under the surface is still worth trying, though.
I love all this. One aspect of doing scientific investigation is looking around you (or whatever you’re using to look around) and seeing what there is to see, inventorying it, and then figuring out what you can do with the tools at hand. And in so many cases, nature provides! It’s funny to think that rocks from space can hit a bigger rock from space, and from that we can make all sorts of measurements, even from tens of millions of kilometers away.
But this is why we explore space, why we send rovers and landers and orbiters and flybyers to other worlds. Sometimes we don’t know what we’ll measure until we get there, and we won’t even know how we will measure them until we get there. But once we’re there, entire worlds are open for us to investigate.
No, There’s No “Huge Blue Globe” in Front of the Sun (Sigh)
For reasons that elude me now, I decided to check on Facebook on Sunday night before going to bed. On the right sidebar, I noticed that it said that “NASA” was trending. That surprised me; had I missed some important event or amazing new Hubble image being released?
I clicked on the link, saw the news item, and let out a long sigh. This is what I saw:
Yup. Another “Space telescope takes a picture we don’t understand and therefore it must be a UFO/Nibiru/NASA coverup/End times/cats-and-dogs-living together situation.” In this case it’s a huge blue globe appearing “in front of the Sun.” Except, of course, it’s nothing of the sort.
Pardon my snark, but this ain’t my first rodeo here. I’ve had to debunk stuff exactly like this dozens of times, and it’s almost always the same story.
On the Facebook trends page there were links to a few articles, the first being to that epitome of accuracy, the U.K. tabloid Daily Mail (for context, I heard the Mail got a science story right once, but I’ve never been able to verify that). The article quotes people making a lot of breathless claims, like the Sun “reacted” to the sphere, or that it might be a “rouge [sic] planet.” A photo caption claims it’s a huge blue sphere and it’s “mystifying scientists.”
Sure. Except no.
I’ll explain in a sec, but first things first: How did this all start? Apparently, a woman named Pamela Johnson posted about this on Facebook, which got the ball rolling. It’s an image from NASA’s STEREO A spacecraft, one of a pair of probes orbiting the Sun. They were launched in opposite directions, designed to take images of the Sun from different angles, and provide a more global view of our tempestuous star. STEREO B has been having some issues lately due to hardware problems, but STEREO A is still ticking along, on the other side of the Sun from the Earth.
The image is weird, certainly. Johnson makes some, um, unorthodox claims about it involving New Age things that I won’t delve into.
Being more of a sciencey persuasion, I looked at the image carefully to try to figure out what I was seeing. I went to the STEREO image search page and found images from that date. Quite a few show the anomaly, while others don’t. At the top of this article is a cleaner shot of one of the images, taken on Thursday at 17:29 UTC.
The two bright spots with vertical lines going through them I recognized as planets right away; planets are bright and overload the detectors a bit, bleeding light into neighboring pixels (this is called blooming and happens all the time in digital detectors, including spacecraft that observe the Sun; UFO hunters and Planet X conspiracy theorists tend to go bananas over such things). Incidentally, the planet to the lower right is Venus, and the one closer to center is … Earth! Because STEREO is on the other side of the Sun, the Earth is in its field of view. So that’s us! Cool.
As for the giant blue ball, that’s no mystery: It’s the Sun. I mean, clearly that’s what it is. The real question is why it appears to be superposed on the image of the planets.
Briefly, the image comes from an instrument on STEREO called the Sun Earth Connection Coronal and Heliospheric Investigation, or SECCHI. This has several detectors on it, including the Heliospheric Imager, or HI, which is a visible-light camera designed to look at the Sun’s corona, its faint atmosphere that streams into space. [Update: To be clear, it doesn't point directly at the Sun, but instead off to the side to better see the corona.] The image showing the two planets is from HI.
But the image of the Sun is definitely not in visible light. I knew right away it was either in ultraviolet or X-ray; the Sun writhes and fumes under its intense magnetic fields, and that’s best seen at those higher energy forms of light.
So why is there a visible light image combined with a UV one? Instead of supposing there are higher dimensional beings warning us about the oncoming Trump presidency, I did something truly silly: I contacted some scientists involved with STEREO who might know the actual answer. Karen Fox, Joe Gurman, and Alex Young at NASA’s Goddard Space Flight Center quickly got back to me. The answer is pretty simple, and makes perfect sense: Sometimes, the image processor onboard STEREO gets overloaded, and becomes “confused.” When that happens, the images get corrupted, and sometimes two images from two different cameras get combined.
That’s precisely what happened here. The HI image was combined with one from the Extreme Ultraviolet (aha!) Imager, producing the bizarre image seen. EUVI takes images at various wavelengths of UV light (think of them as different colors), and this one is from a 17.1 nanometer image, which is where highly energized iron atoms emit. These trace the Sun’s activity well, and that’s why the image shows so many interesting features. The bright spot is where magnetic activity is especially intense, most likely due to a sunspot.
I found an EUVI image from around the same time as the weird one. The features were very similar. I rotated and flipped it to match the HI image (different cameras have different orientations and readout directions); here they are side by side.
Not-so-incidentally, each wavelength seen by EUVI is displayed using a different color to help distinguish them. They aren’t true colors—our eyes can’t see in the ultraviolet—but done as a way to easily identify each wavelength and keep them straight. The EUVI 17.1 nm images are colored blue. So it’s not a “huge blue sphere.” It’s a huge ultraviolet one that’s been colored blue.
AKA the Sun.
So there you have it. No conspiracy, no higher power. Just a glitchy computer.
Of course, another way to think about it is this: It’s a glitchy computer in a space probe launched in 2006 on a huge rocket that took it around the Earth’s orbit to the other side where it uses a complex and sophisticated suite of powerful scientific instruments to track our Sun in wavelengths invisible to the human eye so that we can better understand what it’s like to live in the outer atmosphere of one of the Universe’s most mighty denizens: a full-blown star.
Reality is WAY cooler than nonsense.
What the Heck Is Going on at the North Pole?
I’ve written quite a bit over the past few years about the death spiral of sea ice at the North Pole. Every year the amount of ice goes up and down with the seasons, growing in winter and declining in summer. But, on top of that there has been a trend downward, such that year by year we see less ice all the time.
Because of that we tend to see records set nearly every year. For example, this year in March the Arctic sea ice reached its maximum extent,* but it was the lowest maximum extent ever seen since satellite records began in 1979.
Starting in September every year the ice begins to reform, growing to a maximum. It reached that point on Sept. 10 this year, when it had the second lowest extent on record. After that day, though, it started to grow again.
Except … it didn’t. It started to, but then in early October the growth just stopped. A couple of weeks later it started to rise again, but stalled a second time in late October. In the weeks since then the amount of ice has actually fallen a bit. We are now at record low ice for this time of year, and have been for weeks.
Mind you, it’s winter up there. The Sun shines at most a few hours a day at the southern edge of the Arctic Circle right now. Yet temperatures in the Arctic are soaring; in mid-November it was an average of a staggering 22° Celsius, or 40° Fahrenheit, above normal.
Holy cripes. What the hell is going on?
The obvious answer is: global warming. Like I said, as time goes on, average temperatures go up, and amount of ice decreases.
But there’s a less obvious but more important answer, too. And that is: global warming.
That’s not a typo. The proximate cause of the temperature spike has been a weak jet stream. That blows around the pole, and generally keeps the cold air up there and the warm from the south away. But the jet steam has been weak lately, and warm air has been able to push up into the Arctic and keep temperatures up.
So why is the jet stream weak? Yup. It’s global warming. One thing that powers the jet stream is the difference in temperature between mid-latitudes and the more northern ones. As the planet warms, that difference has fallen (the Arctic warms faster than lower latitudes do), and that has weakened the jet stream.
But there’s more. Because the planet is warming, the sea surface temperatures are going up as well. Water that’s usually frigid in October (like the East Siberian and Barents Seas) has been warmer, so ice growth is slow.
There’s a subtle thing happening here too that’s important. It’s not just that we’re seeing slower ice growth, but the high temperatures are actually melting old, thick ice as well. So it’s not just the extent that’s dropping, it’s the volume as well. That’s important because thin ice comes and goes, melting faster in the summer, but the old thick ice should be here to stay. That’s no longer the case; we’re losing that too.
Here are two videos showing that. The first, from NASA, shows a map of Arctic ice over the years:
The second, by Andy Lee Robinson, shows this even more clearly using a graphical approach:
I have to add that another graph has been making the rounds, showing the total global sea ice extent. It’s troubling as well, but it comes with a caveat. Here’s the graph:
This follows the amount of sea ice at both poles, Arctic and Antarctic. It’s not really a good way to understand what’s happening because the physical conditions at the two poles are very different, and the amount of ice at each is ruled by different circumstances. Combining them just confounds all this.
Right now it’s approaching summer in the Southern Hemisphere, and we expect Antarctic ice to decline. However, even so, it’s falling faster than usual, and the extent there is lower than normal, too.
I include this graph because so many people are talking about it, and it’s important to understand that scientists don’t usually combine the two poles into one graph that way.
However there’s a second point to make as well. Whenever I write about Arctic ice, a herd of climate change deniers converge in the comments and on social media, barking about how Antarctic sea ice is unchanged or even on the rise. But—shocker—that’s crap. The two are unrelated; Antarctic sea ice tends to be relatively steady year to year, and, as you can see, despite that it is pretty low right now.
And they also ignore the fact that Arctic ice has been steadily decreasing for decades. Well, steadily until the past few weeks.
It’s possible that the boreal ice will get its act together and start growing again this season. It’s also possible it won’t. Time will tell.
But time is not on our side. It’s entirely possible we’ll see our first ice-free Arctic summer in just a few decades. Not centuries, or even a century. But maybe by 2040.
The reason this is a concern is twofold. One is that as the northern ice melts, it dumps a lot of fresh water into the oceans. This changes the salinity of the oceans, and that changes how the water flows from the Arctic to the equator and back again. This heat exchange powers a lot of our climate and weather, so having this break down is, in a word, terrifying.
Second, the Arctic is our climate canary-in-a-coal-mine. Because it’s so sensitive to warming, studying it shows us what we’re in for as our planet inexorably heats up.
*Extent is a term climate scientists use, and it’s a little different than just the area of the ice. When they measure the ice they divide the area into regions, and if a region is more than 15 percent ice they say it’s ice-covered.
This Is NOT the Milky Way. Except It Is.
In 2013, the European Space Agency launched the Gaia astronomical observatory. Its mission: Map the positions and motions of a billion stars in our galaxy. Yes, a billion.
The first data release was pretty cool, and some of the early release images were lovely as well. In 2015 the ESA released a nifty map of the Milky Way generated by Gaia data, but it wasn’t actually a photograph: They used engineering data from the observatory itself to map out where stars in the sky were, with denser patches mapped as brighter. Because the image is large and the resolution high, it looks like a photo.
Zen Pencils Takes on Science, Religion, and Relativity
Regular readers may be familiar with Gavin Aung Than’s wonderful web comic Zen Pencils: He takes famous quotations (or quotations from famous people, or just really, really good quotations) and draws a comic around them, illustrating them in ways that augment and expand their meaning*.
In a recent comic, he illustrated the wonderful words of Albert Einstein, who was describing how a sense of mystery is the foundation of both religion and science. Than uses a perhaps anecdotal scene where Einstein saw a man fall from a tree, which gave him the idea of the Equivalence Principle— that accelerating due to gravity and simply undergoing a force are the same thing.
I suggest you read the whole thing, as it’s lovely. Einstein commonly waxed poetic at the profound nature of science, and its fundamental ability to help us understand the Universe, and when he did he was quite moving.
And yet, I have to quibble with the Good Doctor. It’s a good quotation, but I don’t think mystery is the foundation of religion. I am not an historian, but from my own readings it seems to me that mystery was the jumping off point of most religions; the desire to explain the things we see around us and to answer the big questions.
But for most religions today, they claim to have the answers, and that removes the mystery. Oh, sure, there are bits about “God moving in mysterious ways” and other passages in religious texts, but these have always struck me as telling their adherents not to question, not to wonder why. Just accept.
Not all religions are like that, of course, and many religions have sects and subsects with different interpretations of their holy books and how to implement their words.
But what I like about science is that it doesn’t claim to have answers. It has methods. Yes, we do get answers, and many times they’re pretty solid. But science is all about leaving a little bit of room for further data, for an observation that doesn’t fit, for some new discovery to append or upend what we already know. Newton overturned Aristotle, and Einstein himself put Newton’s work into a larger framework; he didn’t negate it, but put it in context and showed where it could be more accurate.
I also quibble with Einstein’s phrasing, “This is religiousness.” In my opinion a better word for that would be numinous, which is arousing spiritual emotion. That’s different than actual religiousness in my book.
But like I said, these are quibbles. His point is solid, and I agree with it: There is a depth and profundity to science for those who pursue it honestly and with an open mind. The language of the Universe is written in the behavior of the Universe; science and math are how we read it.
* Full disclosure: He also made a comic out of one of my own blog posts, making it approximately a bazillion times better.
The Supermoon and Global Warming: A Taste of Things to Come
There is one real thing about the “Supermoon”: It causes flooding. But it needs help in the form of global warming.
I wrote about the so-called “Supermoon” on Monday. The basic idea is that we get a “Suupermoon” when the Moon is full at the same time it’s also at its closest point to Earth in its orbit. According to the lore, the Moon will look bigger and be brighter.
While technically true, these claims tend to be overhyped and breathless, leaving people thinking they’ll see a ginormous Moon in the sky. That’s not the case; as I point out in the article earlier this week the “Supermoon” is only about 10 percent closer than it is when it’s at apogee (the farthest point in its orbit from Earth). You’d never notice the difference in size unless you measure it. It does get brighter, by about 20 - 30 percent, which again is tough to notice on your own.
But there is one thing I didn’t mention in that article, and this is a very real and potentially disastrous effect: Tides.
Time and Tides
Tides are complicated. How they work has been argued for centuries (Newton tackled them back in the 1600s!), but in the end it has to do with the way gravity works. I go over this in detail in my episode of Crash Course Astronomy: Tides:
Here’s a quick overview: The strength of gravity weakens with distance, so the Moon’s gravity pulls harder on the near side of the Earth closer to the Moon than the far side. This stretches the Earth a bit, making it somewhat egg-shaped. Measured from the center of the Earth, both the near and far side of the Earth bump outward a bit, pulled up by the Moon’s gravity. The way gravity works, these are places of lower gravitational potential, so fluids will flow in those directions. Water is a fluid, so it flows to these points, creating high tides, one at each “end” of the Earth. That’s why we get two high tides per day; the Earth’s rotation sweeps you past these two high tide points every day.
During a “Supermoon”, the Moon is closer to Earth. Its apparent size in the sky grows as distance shrinks — make the Moon 10 percent closer and it looks 10 percent bigger. Its brightness grows as the inverse square of the distance — make it 10 percent closer and it looks 1.1 x 1.1 = 1.21 = ~20 percent brighter.
But tides work with the cube of distance, so if the Moon is 10 percent closer the tides are 1.1 x 1.1 x 1.1 = 30 percent higher than when the Moon is farther away. The higher high tides we get when the Moon is close are called proxigean tides, and they happen every month. The unusually close Moon on Nov. 14 meant they were somewhat higher than normal, even for regular proxigean tides.
But there’s more. The Sun creates tides on the Earth, too. It’s far more massive than the Moon, but much farther away, so in the end contributes about half as much to the tides on Earth as the Moon does. When the Moon and Sun are in a line these forces all add up, creating even higher high tides (and lower low tides) than usual. We call these “spring tides”, and they happen twice a month, when the Moon is full and when it’s new.
So the “Supermoon” pulled a double whammy: It was closer than usual, and full, so tides were especially high earlier in the week. We had, and still this week are still having, proxigean spring tides.
The Rising Seas
If things were normal, that would be bad enough. Coastal areas prone to flooding see higher tides twice a month due to spring tides, and also higher tides once a month from the proxigean tides. When they line up it’s worse, but generally not catastrophic.
Unless, that is, a third force comes along. For example, if this happens when there’s a storm, off shore, things can get very bad. Low-pressure systems (like hurricanes or just big storms) draw water toward their centers. If one comes ashore, this can create a storm surge, inundating low-lying areas.
But there’s yet another factor here, and it’s the most pernicious of all: sea level rise.
Global warming is melting ice at the poles (yes, at both poles), and also causing water in the oceans to expand. This is causing the sea levels to rise up over time, by about three millimeters per year. That may not sound like much, but it adds up, year after year. It’s risen 85 mm — over three inches — just since 1993!
As Tamino points out at the Open Mind blog, this alone is enough to cause flooding in coastal areas like Miami and Boston during a normal high tide.
Proxigean tides aren’t normal; they are extra strong. That’s why the NOAA issued a coastal flood warning not just for Monday but for this whole week up until tonight. It’s not until then that the Moon moves away enough both from the Earth and the Earth/Sun line to weaken tides sufficiently to relent on flooding.
But there was flooding, in Portland, Maine, Charleston, South Carolina, and many other locations. From what I can find it was bad but not devastating. It’s what Tamino calls nuisance flooding, and — pardon the expression — it’s on the rise.
In other words, and to be very clear: Global warming is causing sea level rise, which is causing more flooding all the time, and it will get worse. A lot worse.
Remember the “superstorm” Sandy that hit New York City in 2012? It caused huge amounts of damage to flooding, and was itself linked to climate change. It also happened during a full Moon, when tides were worse. Every millimeter of sea level was important there; had it been a proxigean tide as well damage would have been even worse. As it was, it was near apogee (about 400,000 km away) so at least in that sense the effect was minimized. But sea level rise played a critical role there in the flooding.
Moon with a View
I’ve been saying the Supermoon is almost all hype, exaggerated by media. But in this case it really does have an effect, and nature itself will amplify it more and more, year by year. Global warming is making that inevitable.
I cannot end this without stating the glaringly obvious, and doing so bluntly as well: The election of Donald Trump as President is and will be an epic disaster. I mean that literally. With a Republican President who is demonstrably easy to influence, cabinet choices that are the height of assininery, and a Republican Congress all too willing to deny global warming and obstruct any and all attempts to do anything to mitigate it, we are facing a threat to our national security, our nation, and our way of existence. Every year, every month we wait to take action, has huge ramifications down the road.
It’s up to all of us to stay vigilant, and to act as resistance to the denial of reality by the GOP. We have just been handed a big setback, and one with global ramifications, but — hopefully — it won’t be forever.
Ice Crystals Above Clouds Dance to the Tune of Electricity
It looks like the cloud itself is writhing!
After I saw the video, I contacted a meteorologist I knew, and he was able to find the probable cause.
First, clouds can generate enormous electric fields, generally due to rising and falling ice crystals rubbing against each other. The charges separate, and if enough of them build up, they reconnect electrically—via lightning. A typical bolt of lightning can have tens of thousands of amps of current flowing, which is a lot.
Sometimes, long, needlelike ice crystals form in the air above a cloud. They can get an electrostatic charge, like when you rub a balloon against your hair. When they do, they tend to align themselves along the electric field of the cloud. When a lightning bolt discharges, the electric field of the cloud changes suddenly. This changes the orientation of the ice crystals all at once, so what you see is a flash of light whipping around. The general name for this effect is a crown flash (though it’s sometimes called a jumping sundog; “sundog” is itself a nickname for parhelia, bright spots 22° away from the Sun and parallel to the horizon, caused by ice crystals reflecting sunlight).
At least, this is what has been supposed. A new paper in the open-access Journal of Applied Mathematics and Physics put this to the test. They modeled the ice crystals using a ferrofluid, mineral oil with tiny iron-based nanoparticles suspended in it. When a magnetic field is applied, the particles line themselves along it, forming bizarre and lovely shapes. Here’s a cool video (unrelated to the cloud research) showing how they work:
In this new work, the scientists bounced a laser (representing sunlight) off a ferrofluid, and showed that the direction in which the beam got reflected changed as they repositioned the magnet, and it happened in a similar way as the real crown flashes above clouds. While this doesn’t prove the proposed explanation, it strongly supports it, and I find this hypothesis pretty compelling.
I’ve never seen a crown flash myself; they’re pretty rare, and the geometry has to be just right to create them. Maybe someday.
But I do get a consolation prize. The reason I heard about this research is that I was notified by the paper’s lead author Alberto Tufaile on Twitter. It turns out he found out about the phenomenon by reading my article on it! He and his team even reference it in the paper:
(That was from when my blog was hosted by Discover Magazine, if you’re curious; I moved to Slate in 2013.)
How cool is that? I don’t think my blog has ever been cited in a science paper before, much less been the starting point for the research itself! And, why yes, before you ask, I am pretty chuffed with myself over that.
But the real takeaway here is that there is stuff going on literally right over our heads that we still don’t fully understand, and may not even know about yet. So—and I bet you know what I’m about to say here:
Look up! You never know what you might see.
An Eerie Hex on Saturn
Two things I love: astronomy and cool clouds. I love them even more when I can enjoy both at the same time.
The image above is of Saturn, taken by the Cassini space probe on Sept. 5, when it was about 1.4 million kilometers from the planet, using its wide-angle camera equipped with a filter that lets through near-infrared light. This is just outside what our eyes can see, and it emphasizes the location of methane gas in Saturn’s upper atmosphere.
That hexagon, though! It’s so creepy looking, like it’s artificial, a construct. But it’s natural. It’s something like our jet stream, a circulating wind pattern that blows around the planet. These are called Rossby waves, and they’re powered by the planetary rotation. You also need a sharp wind gradient, a rapid change in wind speeds. On Saturn this happens at high latitude, near the north pole, which is why the hex forms there.
The video below shows this really well; scientists mounted a camera above a rotating cylinder filled with water (the camera spins with the cylinder, so the rotation isn’t apparent) and put a smaller disk inside it that spins more rapidly. Watch what happens as the fluid interacts with itself:
Boom! Hexagon. How cool is that?
Of course, Saturn’s hex is somewhat bigger: It’s 20,000 kilometers across, big enough to swallow the Earth with plenty of room left over.
If you need some scale, here’s an older shot from 2012 that’s in enhanced color:
See that white spot to the lower right? It’s bigger than Texas. So there’s your scale for you. Saturn is immense.
By the way, it looks like Neptune has a well-defined hexagon at its south pole as well. I still haven’t been able to confirm this, but the image of it is pretty compelling. Uranus and Neptune aren’t as well observed as Saturn, because we don’t have orbiters there. Cassini has been tooling around Saturn for 12 years now, so it’s seen a lot. The mission is scheduled to end next year, but it’s been one of the most successful space adventures humans have ever undertaken. And the stuff we’ve seen from it … Saturn will continue to mystify us for generations.
I am constantly surprised by how the Universe can constantly surprise us. That may be one of the most fun aspects of science.
So, About Today’s Supermoon …
Hey, have you heard about today’s “Supermoon”? If you have, then chances are you’re heard a lot of hype about it being superclose and superbright and super, uh, super.
Except not so much. I mean, the stories are accurate as far as they go, but you need to put them in context. Yeah, the Moon will be closer than usual when it’s full, but by a margin so small it’s essentially meaningless. Let me explain …
But first, let me be clear: I always always urge people to go out and look at the Moon! It’s beautiful and fascinating and wondrous. If you can, use binoculars or a small telescope to get an even closer look; it’s an entire world hanging in the sky so there’s a lot to explore. Craters, impact sites, mountains, and more … it’s simply awe-inspiring.
But I want your sense of awe to be honest, and honestly stoked. This Supermoon stuff isn’t the right way to do it.
So what’s a “Supermoon”? It’s not a real astronomical term—it was actually coined by an astrologer, so don’t even get me started here—but in the popular vernacular it’s when there’s a full Moon within a few hours of the Moon being closest to Earth.
The Moon orbits the Earth on an elliptical path, so sometimes it’s closer to us than other times. Monday, the Moon reached its closest point to Earth (called perigee) at approximately 11:20 UTC (06:20 Eastern U.S. time†) when the center of the Moon was just a hair under 356,508 kilometers from the center of the Earth (astronomers like to use the centers of objects to measure distances, to avoid messy circumstances like nonspherical surfaces).
As the Moon orbits the Earth, its phase (the amount of lit surface we see) changes. When it’s near the Sun in the sky we see it’s dark, unilluminated side facing us, so we say it’s new. Two weeks later it’s opposite the Sun in the sky, and we see it fully illuminated, and we say it’s full.
Monday the Moon was full at 13:52 UTC (08:52 Eastern). That’s just a couple of hours after it was at perigee, hence the Supermoon stuff.*
But what does that really mean?
On average, the Moon’s perigee distance is roughly 360,000 km from Earth. Also on average, it’s about 405,000 km away at its most distant point (called apogee). That’s about a 10 percent difference. That in turn means the Moon looks about 10 percent bigger when it’s at perigee than at apogee.
That’s not much! And those are the extremes, too. If you’re an experienced lunar observer you might notice that difference, but for an average person I’d expect you wouldn’t be able to tell just by looking. The Moon is pretty small on the sky, far smaller than you think. Let me ask you this: If you held up a dime, how far away from your eyes would it have to be to appear the same size as the Moon? Here’s the answer, and it may surprise you. The point? A 10 percent change in size isn’t a big deal (and be careful not to be confused about the famous Moon Illusion, when the Moon looks bigger when it's on the horizon; that really is an illusion, and happens whether the Moon is near perigee or not).
It gets worse. Monday’s “Supermoon” is supposed to be closer to Earth than it has been for decades. That may be true, but by how much? The last time a full Moon was this close was on Jan. 26, 1948, when it was 356,462 kilometers away. That’s a difference of just 45 kilometers or so closer than it was Monday! Remember, this is the distance between the Earth’s and Moon’s centers … and the Earth is nearly 13,000 kilometers across! So this small difference in records is completely wiped out by the simple fact that someone standing on a different part of the Earth might be thousands of kilometers closer or farther from the Moon.
That’s why I don’t particularly care for glorifying “records” in cases like these. It may be true numerically, but in practical terms it doesn’t make any real difference.
Another Supermoon claim is how bright it’ll be, too. It’s true that an object closer to you will appear brighter, and it’s a strong effect. In the end the Moon will be about 20-30 percent brighter than a usual full Moon. That may be enough to notice, but atmospheric conditions (clouds and haze) could easily affect that, and it’s hard for people to simply compare one full Moon to another, because you have to remember how bright it was last time, a month ago, and that’s hard to do. I’m not saying you won’t notice! But the hype makes it seem like the Moon will be vastly brighter; a powerful orb searing the heavens.
In reality, the full Moon is pretty bright anyway. If you notice the difference, terrific! But always be a little bit skeptical.
All in all, stuff like this “Supermoon” makes me conflicted. I love the idea that people will hear about it, go outside, and take a look at our nearest cosmic neighbor … especially if they otherwise wouldn’t. Getting people to go out and look up is a good contender for my Astronomical Prime Directive.
But I think they should be armed with the facts when they do, and be doing it for the right reasons. The right reasons are that the Moon is gorgeous, ever-changing, and honestly really fun to observe. Those are, in my opinion, the reasons you should go out and see it.
Either way: Go out and look up. Watch the Moon! When you do, you’ll realize it’s always super.
I’ve written about the Supermoon many times. Here are a few articles for your edification:
*Note that both these times are during the day for the U.S. That's OK; if you saw the Moon on Sunday night or wait until Monday night it'll still look full, and still be near perigee. It rises around 5 p.m. to 5:30 p.m. local time for you (it depends a bit on where you are in your time zone; check your local listing).
† Correction, Nov. 14, 2016: I originally wrote that 11:20 UTC was 07:20 Eastern time.
Time Lapse: Refraction
Air bends light.
Well, OK, not exactly. A beam of light could pass through air all day long (as long as you have a layer of air 26 billion kilometers long) and not deviate a whit. But if the density of that air changes, the light will bend. This is called Snell’s law, and you’re already familiar with it: It’s why a spoon in a glass looks bent or broken; the light from the spoon bends as it passes from water to air, distorting what you see.
The Earth’s atmosphere has layers to it, thin blankets of air of varying temperatures and densities due to winds carrying, for example, a layer of warm air over a colder one. Light passing from one layer to another gets its direction changed slightly, what scientists call refraction. This distorts our view of objects in space; on its way to our eye the light from stars passes from one layer to the next and refracts. The results can be quite dramatic.
The star trails images were shot in Chile (did you notice the stars appear to set “backward,” from right to left, compared with the way we Northern Hemisphere observers are used to?). Without an atmosphere, the animation would show the stars moving along graceful, smooth arcs, appearing to set as the Earth rotates under us.
But we do have air, and so instead the lines squiggle, moving back and forth. I have to admit, that took me a moment to understand. Refraction in these cases should bend light down, not left or right! But that’s actually what you’re seeing. As a star moves down, and appears to pass through different layers of air, its light is bent down, making it appear as if the star is higher than it really is. But at the same time, the star is moving down and to the left. The refraction makes the apparent vertical movement of the star slow, but it’s still moving to the left. The result is that the star appears to move mostly left, causing the sideways jiggle.
The effect is more dramatic when you see the setting Sun (or Moon). Stars are points, so they appear as lines in the time-lapse. But the Sun is a disk on the sky, and its shape distorts profoundly as its light passes through different layers; it gets squeezed and pinched. That’s because as the Sun sets, the light from different horizontal slices of it move through different layers of air.
Picture the Sun on the horizon, sliced in half by it. The disk of the Sun is thickest on the bottom (where you see its full diameter) and gets narrower as you go up. The air layers are horizontal, and might slice across different widths of the Sun’s disk. If light from a narrow slice gets bent enough it might appear to be below a thicker slice, and the Sun looks pinched.
I know, that’s all very weird. But there’s more: The amount of bending depends on the color of the light as well. Bluer light bends more than red, and that can change the color of what you’re seeing layer by layer. In the part of the video where the Sun is setting, some layers look red, orange, and even green! This can cause the so-called green flash, when you can see a brilliant green flash of light from the Sun just as the last bit slips below the horizon. I saw this for the first time in my life recently when I was standing on the upper deck of a small boat on the Pacific Ocean, and it was amazing. The effect is so particular that people standing on the lower deck, just a couple meters lower than me, didn’t see it at all!
If it’s hard to parse all this, I totally get that; these kinds of things can be hard to wrap your head around unless you’ve had experience thinking about them. But if you take away anything from this, it’s this: Light can bend, things aren’t always as they seem, and even something as simple as watching the stars rise and set can lead to profound insight into fundamental ways the Universe works.
Learning about everything begins with noting something and thinking about it. It’s a pretty good way to go about life.