Crash Course Astronomy Episode 7: Gravity
I was traveling last week and couldn’t put up a post about Crash Course Astronomy when it came out. So, belatedly, here is Episode 7: Gravity!
Writing these episodes can be a tightrope walk. Gravity is an interesting topic; since we’re still early in the series, I wanted to go over the aspects of gravity we’ll need to talk about planets and moons, asteroids and comets. That means discussing it as a force, how it makes things move, how orbits work, and the difference between mass and weight. That also means not getting into things like how gravity curves space, and why massless photons are still affected by gravity. I mention it but don’t go into details. Think of it as a teaser for a later episode.
I wrestled over discussing how gravity is a force that accelerates things. This is part of Newton’s Second Law of Motion: A force acting on a mass will accelerate it.* The gravity of the Earth is independent of the mass it’s working on; it’s a property of the Earth itself. If you drop two objects of different weights, they’ll fall at the same rate (ignoring air resistance). My friend Brian Cox demonstrated that quite ably.
The objects will accelerate, which means that the longer they fall, the faster they’ll go. That acceleration is a property of Earth’s gravity, and will be the same for any object. Drop a ball near the ground, and it will accelerate at a rate of about 9.8 meters per second for every second it falls. After one second it’s moving at 9.8 m/s. After two seconds it falls at 19.6 m/s, and so on.
But the force it feels is different than a ball that has a different mass. That’s the weird part that can be confusing. Gravity accelerates everything the same, but if you have more mass you feel more force. When it comes to gravity, we call that force weight. Because the force is bigger we think a more massive ball will fall faster, but it doesn’t because the acceleration is the same as it is for a less massive ball.
But if you want to stop a heavier ball, you’ll have to apply more force than you would on a lighter ball. When the heavier ball hits the ground, it hits harder than the lighter one, even though they’ll impact at the same speed.
Now, did you notice the verbal switcheroo I just pulled? I talked about the more and less massive balls in one paragraph, then called them heavier and lighter in the next. That’s sloppy (though I did it on purpose to prove a point)! In deep space, with no (or negligible) forces acting on them, they both weigh the same: nothing. But their masses are different. Wheee!
If you think you get this now, yay! Good. But here’s a test: What weighs more: a 5 pound helium balloon, or a 5 pound block of cheese? The answer may seem obvious, but explaining it isn’t all that easy.
Maybe I’ll need to make a bonus video with that. I’ll need a big balloon. I wonder if I can get George Clooney and Sandra Bullock to guest star?
*Actually an unbalanced force; if you have another equal but oppositely directed force acting on it, the object won’t accelerate. If it’s moving it’ll still move, but if it’s just sitting there it won’t start to move. See why you need to simplify sometimes? You just need to be careful that you don’t oversimplify and make things worse. That’s another reason writing these episodes can be tricky.
The Week in Political Buffoonery
As someone who understands science and math, I know that when you look into a particular population looking for instances of a particular behavior, sometimes those behaviors will cluster in time. You might go a few weeks with very few instances, and then suddenly see a big clump of them happening at the same time.
Of course, when we’re talking anti-science buffoonery in politics, there is a vast, vast sample size. The statistics are pretty good.
Still, last week there were a large number of forehead-smackingly nonsensical ridiculosities. Out of them all, here are three guaranteed to put a dent in your desk where your head slams into it.
1) James Inhofe Disproves Global Warming Because Snow
Sen. James “Global warming is a hoax” Inhofe (R-Oklahoma) has never met an argument against climate change too silly and obviously wrong not to repeat. Last week, he actually stood on the floor of the United States Senate, and talking about global warming, he—and I can’t believe I’m typing this—pulled a snowball out of a plastic bag and said,
I ask the chair, you know what this is? It’s a snowball, just from outside here. So it’s very, very cold out. Very unseasonal.
Yes, Sen. Inhofe, it snows, because it’s winter. The planet is warming up, but it still gets cold in the winter (at least it does for now). If your average low temperature in February is, say -10° Celsius, then it can warm up a few degrees and still be below the freezing point of water. That’s grade-school math.
Clearly, Inhofe is an Axial Tilt Denier, too. I wonder how he’d feel knowing that he has a lot in common with a Saudi cleric.
As Stephen Colbert has said, the idea that winter disproves global warming is like nighttime disproving the existence of the Sun. If you want details, Jon Stewart did a great job slam-dunking the it’s-cold-outside-therefore-no-global-warming dumbosity.
Snark aside, Inhofe’s head is quite firmly in the sand, and he’s an embarrassment to the Senate. I hope this is his “Michael Dukakis in a tank” moment. Thank heavens another Senate member, the wonderful Sheldon Whitehouse (D–Rhode Island), took him to task for this.
2) House Science Committee Member Doesn’t Vaccinate
Speaking of dangerous rhetoric, on the House side, Rep. Barry Loudermilk (R-Georgia) took a moment in a public town-hall meeting to let everyone know he didn’t vaccinate his kids:
Great, huh? He tried to follow up later saying he’s not against inoculation, but it’s clear he doesn’t understand the issue (and by the way Jenny McCarthy says she’s not anti-vax, either). And we know Tea Partiers tend to be anti-vax as well, though it’s usually about being anti-government, not anti-science per se.
Did I mention Rep. Loudermilk is on the House Science, Space, and Technology Committee? It may be past time to change its name.
And Rep. Loudermilk, when a GOP strategist tells you to resign over something ridiculous that you’ve said, you really, really need to rethink your position.
3) A Load of Taurus
American politicians don’t hold the monopoly on anti-science nonsense. Unhappily, facing away from reality knows no country’s borders. Case in point: Tory MP David Tredinnick thinks that a lot of the U.K.’s health problems could be helped by turning to astrology.
Just go to that link and see if you can count how many logical fallacies he relies on to back up this sentiment. Have a calculator handy. In the meantime, I’ll just leave this here.
So yeah, I’m being a bit snarky, but remember, these are critical topics—the environment, public health, and the health of science itself. If these politicians are willing to dump evidence-based reasoning by the side of the road, then what else are they willing to do? And they make our laws.
It’s time to dump them. If your representatives don’t believe in reality, then next election time it’s your responsibility to show it to them.
Me vs. Hank Green: SciShow Quiz Show
Part of the vast Hank and John Green video empire includes SciShow, a YouTube channel that has a variety of different science shows on it, like SciShow Dose (quick videos on interesting topics), News, Infusion (longer videos, like the vaccine one I posted about recently), and many more.
They also have Quiz Show, where two sciencey-type people go head to head in a snarky contest to see who knows more science, but which in reality just shows who can guess the answer better than the other.
When I was up at the HQ last time filming some episodes of Crash Course Astronomy they asked if I wanted to be on Quiz Show, and never one to give up an opportunity to make a fool of myself on camera, I said sure. So they pitted me against the man himself, Hank, in a battle of brains. Who will win? Find out for yourself:
So, congrats, Ian! I hope you enjoy your swag. And yes, I was very pleased with myself for deducing the answer to the second question, getting it right for the right reason. SCIENCE!
Ticket to Space
My friend Dan Durda is many things: an astronomer, a planetary scientist, an artist, a pilot.
He’s also an astronaut. Or he will be, very soon.
He works at Southwest Research Institute here in Boulder, Colorado, which is a company that does a lot of work in space; the New Horizons Pluto probe instruments were developed there, for example, and the principal investigator, Alan Stern, is there. Dan’s very interested in the behavior and structure of asteroids, which is difficult to study here on Earth.
So he and his fellow scientists at SwRI got an idea: Go into space.
We’re at the doorstep of cheaper, more reliable access to space. Ticket prices are within reach of wealthy individuals and, perhaps more importantly, companies that do science. A lot of Dan’s experiments can be done easily in the few minutes of weightlessness these suborbital flights provide.
But why not get all this from Dan himself? He recently gave a TEDxBoulder talk about this, and it’s really good.
What he said is true: We’re just starting off doing this work, and we don’t know where it will lead. There have been setbacks, for sure; the loss of the Virgin Galactic vehicle and its pilot last year, and the explosion of the Antares rocket upon liftoff.
As I have written many times before, while tragic, these sorts of losses are inevitable. They are the price we pay for pushing boundaries, and you’ll find most astronauts understand these risks. To use an analogy Dan made in the video, where would be now if airplane crashes grounded the airline industry in the early 20th century?
We’ll continue on, pushing our way into space. Again, as Dan points out, we cannot know where this will lead … except up. And that’s a direction I think we should go.
The benefits of cleaning out your inbox: I somehow completely missed this spectacular image when it came out a while back, but now that I’ve found it I can share it!
That's the Crab Nebula, one of the most well-studied and famous objects on all the sky. It the expanding gas cloud left over from a titanic supernova explosion, in this case the death of a very massive star. The light from this explosion reached Earth in 1054, and in the subsequent millennium the debris has reached a size of well over 10 light-years.
That’s 100 trillion kilometers, just so’s you know.
Kepler-432b: A Doomed Planet Orbiting a Doomed Star
Two independent teams of astronomers have just announced the discovery of an unusual planet with a grim future: Kepler-432b.
The planet orbits a star nearly 3,000 light-years away and was discovered using the Kepler observatory, which looks for telltale dips in star light as a planet orbits a star; if the planet’s orbit is seen edge-on from Earth, then once per orbit it blocks a small fraction of the star when it passes directly between the star and Earth.
Measuring the timing of the dip (and knowing some of the properties of the star) yields a lot of information about the planet, including its size, and the size and shape of its orbit. They also took spectra of the star, breaking its light up into thousands of individual colors, which yields one more crucial piece of information: the mass of the planet. The planet and star orbit a common center of gravity, and as the star moves in its orbit its spectrum changes due to the Doppler shift. This effect is pretty dang small, but measurable using precision instruments.
The results are pretty cool: The planet Kepler-432b is roughly five times more massive than Jupiter, but only about 1.1 times as wide. This makes it pretty dense, about as dense as Earth! Gas giants have a weird property that as they get more massive their size doesn’t increase much—instead, the pressure inside them increases, and their density goes way up. Jupiter is right at about the lower limit where that happens, so planets can be much beefier than Jupiter but not much bigger.
But what makes this system special is the star itself. It’s a little more massive than the Sun, but it’s what we call a red giant: A star that is starting to die.
At some point in the past, the star Kepler-432 ran out of hydrogen fuel in its core. The core of the star is shrinking and heating up, dumping all that heat into its outer layers. What happens to a gas when you heat it up? It expands. And so Kepler-432 has swollen up to a size about four times wider than our Sun. As it got bigger its surface area increased, too, and so, weirdly, the amount of energy coming through its surface per square centimeter has actually dropped, lowering its temperature. Cooler stars are red, so Kepler-432 is a red giant.
It will continue to grow as it ages, swelling to a much larger size than it is now. Much larger. Will it engulf the planet?
It may not grow enough to swallow the planet directly. However, as it gets bigger, it interacts with the planet via tides, and (through a complicated series of steps) will actually drop the planet closer in to the star.
It looks like this one-two punch is enough to doom the planet. The star will grow larger, the planet’s orbit will shrink, and then … doom. The planet will fall into the star, where it will plunge deeper and deeper, until it evaporates completely.
But don’t despair too much. As the planet falls inside the star, it takes a while to disintegrate. It orbits much faster than the star spins, so it may churn up the insides of the star like a whisk in a mixing bowl of batter. The star’s rotation will increase. As the star continues to age, it will fling off its outer layers, exposing the hot core at its center. This very dense, very hot object, now called a white dwarf, will blast ultraviolet light into space, illuminating and exciting the gas it ejected, causing it to glow. Because the star was spinning, this gas can take on fantastic shapes, including double-lobed patterns reminiscent of butterfly wings.
Scientifically, this system is fascinating; we don’t have too many examples of giant planets orbiting red giant stars (which may be in part due to the fact that they tend to fall into their stars!), so every one we find is important. The planet orbits the star on a long ellipse, too, which is unusual and difficult to explain. There are many mysteries to plumb here.
And metaphorically, well, this transformation is almost too on-the-nose: Like a caterpillar, the planet and star will transform into something magnificent, literally a butterfly shape. And it will glow fiercely like that for centuries, its beauty visible easily from telescopes even thousands of light years away.
The Universe is all about change, birth, destruction … and given that, perhaps Kepler-432b’s eventual fate isn’t such a bad one.
Postscript: You can read the papers published by the two teams who studied this planet: Ciceri et al., and Ortiz et al. Their results match pretty well, though, interestingly, Ciceri et al. find no evidence for a second planet orbiting the star, while Ortiz et al. do. Also, Ciceri et al. conclude the planet won’t be engulfed. I don’t think they included the work showing the planet’s orbital radius will shrink, though, which was considered by Ortiz et al., so I tend to agree with Ortiz’s team. The planet is doomed.
Ceres Is Getting Weirder
Dawn approaches Ceres.
The spacecraft Dawn, that is, and the asteroid Ceres, the largest of the rocks orbiting the Sun between Mars and Jupiter. Dawn has been headed slowly toward Ceres for many months now, and only recently has its target been big enough to see as more than a dot.
On Feb. 19, 2015, Dawn took the image of Ceres above from a distance of 46,000 kilometers (29,000 miles; roughly an eighth the distance of the Moon from the Earth). Earlier pictures already revealed a bright spot on the surface, and now the resolution is good enough to see it’s not one spot, but two. Like a distant car on the highway getting near, and seeing its headlights split from one bright glare to two, Dawn’s proximity to Ceres has allowed us to see the shiny spot is not alone.
It’s still too early to say what we’re seeing here. Ceres has a lot of water ice inside it, and it seems likely these spots are related to that. You can also see they’re located in a crater—which isn’t necessarily remarkable; as you can see the whole surface of Ceres is saturated with them. My initial thought was that an impact had revealed ice underneath the surface, digging it up. We see that in some craters on Mars, for example.
But now I wonder. It’s possible that we’re seeing cryovolcanism: literally, ice volcanoes. But it’s hard to understand what would drive that. Ceres is too small to have tectonics and has no moon that might generate tides to warm the interior.
At the moment, it’s a mystery. And that’s good! We've never seen Ceres in this detail before, so everything we learn about it will be new.
For example, look at the large craters on it. They look to me to be flatter than craters that size would be on other worlds. I suspect we’re seeing either a softer surface, or that ancient, big impacts melted ice under the craters which flooded the floors. We see similar things on the Moon, but in that case it was molten rock, not water, that filled the floors.
But I’m speculating, based on what we see so far. And these are still relatively low resolution images; compare them with what we saw when Dawn orbited Vesta, its first asteroid target, to get a taste of what’s coming. Dawn will enter orbit around Ceres on March 6, and will continue to orbit the asteroid for well over a year. What mysteries will it unveil that we haven’t even guessed at yet?
Gavin Heffernan is a photographer who travels to difficult-to-reach locations and shoots simply tremendous time-lapse videos of the landscape and night sky he sees there.
He just sent me a note that he’s created another video, and, well, holy wow. It’s another stunner: “Tempest Vermilion,” shot at the Vermilion Cliffs National Monument in Arizona.
You know the drill: Make it full screen, set it to high-def, crank up the volume, and let your eyes and brain soak it up.
This is the second part of a trilogy of videos Heffernan has created for BBC 2; the first, called “Wavelight,” is online as well. He and his collaborator, Harun Mehmedinovic, are also making a video about the effects of light pollution. Called “Skyglow,” it’ll be on Kickstarter in early April. Stay tuned for that.
In the meantime, take a look at these other amazing videos by Heffernan:
A Supermassive Black Hole’s Fiery and Furious Wind
When you think of black holes, you probably think they are chaotic destroyers of all; wandering through space devouring everything in their path, and once something gets too close, it’s gone forever.
That’s a little unfair. Actually, a lot unfair. They only eat stuff that’s nearby, for one thing. And for another, they’re sloppy eaters. Not everything falls straight down their gullet; a lot of it can swirl around the black hole in what’s called an accretion disk. Material in that disk can be heated to terrifyingly high temperatures, millions of degrees, causing it to glow fiercely bright. It can blast out X-rays, and even create an intensely strong wind of material that flows away from the black hole.
We also know that every big galaxy we look at has a supermassive black hole in its very center. If that black hole has gas and matter falling into it, the accretion disk can be huge and ridiculously, soul-crushingly bright. The luminosity of such an object can easily outshine the hundreds of billions of stars in the host galaxy, and make the black hole visible clear across the Universe.
This sets up an interesting problem. When you have a monster in the middle like that, how does it affect the rest of the galaxy? A curious fact was discovered many years ago; the mass of the black hole in a galaxy seems to correlate with how the stars in the galaxy orbit. You might think “duh” to that, but hang on. Even though a black hole can have a mass of a billion times the Sun, that’s a teeny tiny fraction of the mass of a galaxy with a few hundred billion stars in it.
Somehow, the black hole is affecting the galaxy around it on a huge scale. How?
The obvious way is through this wind, this cosmic hurricane of particles blasting outward from it at high fractions of the speed of light. Studying that wind is maddeningly difficult, though. For example, when we look right at the center of the galaxy, all we can see is the extremely narrow slice of gas between us and the black hole. That gas absorbs the light coming from the accretion disk, blocking it. As it happens, different kinds of atoms block different colors of light. One type of iron, for example, that has a lot of its electrons ripped away from the intense energy blasting away nearby, is really good at absorbing a very specific wavelength of X-rays.
That can tell you something about the gas, like how hot it is, and how fast the gas is moving away from the black hole. But what it doesn’t tell you is the overall shape of the wind. Is it blowing out spherically, like an expanding balloon, or is it focused into narrow beams?
Lots of black holes have those beams screaming away from them. We know this because we can see them. But not every black hole has them. So how can you figure out the shape of the wind?
Some astronomers have just announced they found a way. The black hole they observed is a billion-solar-mass beast in the center of the galaxy PDS 456, which is about 2 billion light-years away. It’s fairly well studied, and is a good example of a typical “active galaxy,” one with an actively feeding black hole in its core.
They observed it using two different observatories: XMM-Newton and NuSTAR. Both can sort incoming X-rays into their individual energies (think of that like color in light we see). XMM-Newton could see the gas blocking the black hole directly, but can’t detect any gas anywhere else. NuSTAR, however, is able to see the kind of X-rays that would be coming from gas surrounding the black hole … and it did. Looking at the spectrum of the X-rays, it found the unmistakable signature of gas expanding outward in a sphere (if you want technical stuff, it saw a classic P-Cygni profile).
This is a big deal. The geometry of the expanding wind can tell us its total energy. Think of it this way: Imagine you have a 1-watt light bulb. It looks pretty dim, because it’s sending light out in all directions. Only a little bit of the light is heading into your eye. But if I have a flashlight, it focuses the energy emitted, so it can gather up all the light being wasted in other directions and beam it toward you. The bulb in a flashlight can be a lot dimmer, but still look brighter to you because of that.
And that’s the basis of these new observations. They saw that the wind from the black hole is expanding in all directions, which means the astronomers could determine the overall physical nature of the wind. It turns out the black hole is blasting a wind that totals 10 times the Sun’s mass every year—and mind you, that vast amount of stuff is screaming out at tens of thousands of kilometers per second. If I’ve done my math right (and I have; I checked), that means the mechanical energy in that wind is a staggering 10 trillion times the total energy the Sun emits every second.
And that wind is blowing outward in all directions, so it can easily affect the gas around it, even thousands of light-years away. This in turn would affect how stars form in a galaxy, and explain the relationship we see between the black hole and the stars in the galaxy around it.
And here’s the really cool thing: We think those big black holes form at the same time as the galaxy itself. As the zillions of tons of gas swirl around in the proto-galaxy, assembling itself into stars, some of it is falling into the nascent black hole in the center of that maelstrom. It forms a disk around the black hole, heats up, and starts to blast out a wind. This wind slams into the gas around it, all around it, blowing it hither and yon.
When the galaxy finally coalesces as a massive island universe of billions of stars, the motions of the stars themselves still have the fingerprint of the black hole’s wind imprinted on them, even billions of years later. And that wind may have helped trigger more stars being born as it rams into and compresses the gas around it, just as it can also shut down star formation by blowing that gas away.
Our galaxy, the Milky Way, has such a black hole in the middle. It’s not a big one as they go, a mere 4 million times the mass of the Sun. But 10 billion years ago, when our galaxy was forming, it may have been active, and may have affected the young galaxy around it as well.
When you go outside at night and look at the stars, think on that. If you can see Sagittarius, you’re looking toward the center of our galaxy, where that monster dwells. It’s surrounded by billions of stars, so distant from us their light merges into a soft glow. But they’re there, those myriad stars, and their motions, their formation, even their existence itself may have been profoundly influenced by a black hole that we didn’t even know existed until a few decades ago.
Ah, science. It allows us to wonder about the inner workings of the Universe we live in, and then shows us how the pieces fit together. If there is a grander, more exhilarating adventure than that, I don’t know what it is.
Why Do Some People Refuse to Get Vaccines?
There’s been a lot of discussion in the media (both mainstream as well as social) about vaccinations, spurred because of the current measles outbreak in the U.S. I’m unhappy about the cause, of course, but I welcome the discussion. I’m just sorry it took an outbreak from Disneyland to get this conversation rolling.
A lot of people are blaming anti-vaxxers for the outbreak, but the truth is more complicated than that. Certainly Jenny McCarthy, Andrew Wakefield, and the organized groups spreading dangerous misinformation about vaccines have their share of it, but their influence isn’t almighty. There’s more to this story.
That’s why I’m glad my friend Hank Green has made an episode of SciShow explaining why people choose not to vaccinate.
Hank’s overview is pretty good, and very well laid out! But I want to add a few things.
One is that this is not just a hippie, liberal thing. Very conservative people, including libertarians, don’t want the government telling them what to do, so state-required vaccinations for children to allow them in schools is anathema to them. I’m not saying they’re right—in fact, they’re very, very wrong—just that this is what they think. Anti-vaccination sentiment is well distributed throughout the political spectrum.
Another is that overall in the U.S., vaccination rates haven’t fallen in recent times. But that casts a mighty wide net. If, instead, you look on smaller scales, you see pockets of low vaccination, regions where rates have dropped dramatically. Sure, some are liberal bastions like Northern California, but other places are affected for other reasons, like the Texas town influenced by a megachurch.
And, as always, I want to point out that I understand how parents feel here. I have a daughter myself, and my wife’s and my concerns for her health were and are strong. So I want to distinguish between parents out there trying to figure this all out, and the people who are actively and vocally trying to confuse them over this issue.
I know how important vaccines are, and my entire family is up-to-date with their vaccinations. I’m walking the walk.
Hank’s audience for SciShow tends to be younger folks, and I hope they take this lesson home (literally as well as figuratively). This issue of bias and evidence goes well beyond vaccinations, into the very trust we have of science itself. That’s something I’d love for younger folks to understand. Science is pretty cool, and the most important tool humans have to understand everything around us.
It also saves lives.
Addendum: Germany is facing a large-scale outbreak of measles as well, with nearly 600 cases since late last year (the population of Germany is one-fourth that of the U.S.). One boy, an 18-month-old, recently died from complications due to measles. My heart aches over this, which is why I write so frequently about vaccination. My thanks to Mat Johnson for alerting me to this.