Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing "Hoax" - Philip Plait (2002)
Part V. Beam Me Up
Chapter 24. Bad Astronomy Goes Hollywood: The Top-Ten Examples of Bad Astronomy in Major Motion Pictures
hoosh! Our Hero's spaceship comes roaring out of a dense asteroid field, banks hard to the left, and dodges laser beams from the Dreaded Enemy, who have come from a distant galaxy to steal all of Earth's precious water. The Dreaded Enemy tries to escape Earth's gravity but is caught like a fly in amber. As stars flash by, Our Hero gets a lock on them and fires! A huge ball of light erupts, accompanied by an even faster expanding ring of material as the Dreaded Enemy's ship explodes. Yelling joyously, Our Hero flies across the disk of the full Moon, with the Sun just beyond.
We've all seen this scene in any of a hundred interchangeable science-fiction movies. It sounds like an exciting scene. But what's wrong with this picture?
Well, everything, actually.
A lot of science-fiction movies are good fiction but bad science. Most writers have no problem sacrificing accuracy to make a good plot, and astronomy is usually the first field with its head on the block. How many times have you sat through one of these movies and shook your head at the way astronomy was portrayed? I spent a lot of my youth in front of the television watching bad sciencefiction movies, and while they did help foment my interest in science, they also put a lot of junk into my head. So in the name of astronomers everywhere, I have compiled a Top-Ten list of Bad Astronomy in movies and TV. Some of these examples are specific and others are generalizations culled from hundreds of movies I've watched late at night or on Saturday mornings. The results are compiled into the scene above.
Let's pick apart that scene and find out just where it goes wrong. Go ahead and make some popcorn, sit back, drink some soda out of an oversized cup, and enjoy the show. And please! Be considerate of others; keep the noise to a minimum. Speaking of which ...
1. Whoosh! Our Hero's spaceship comes roaring out ...
Well, as they say, "In space, no one can hear you scream." Sound, unlike light, needs something through which to travel. What we hear as sound is actually a compression and expansion of the matter-usually air-through which the sound wave is traveling. In space, though, there's no air, so sound can't propagate.
But we live on a planet with a lot of air and we're accustomed to hearing things make noise as they go past us. Cars, trains, baseballs: they all whiz through the air as they pass us by. If we see something moving past quickly and quietly, it looks funny. Andre Bormanis, writer and science advisor for the Star Trek television series, confirmed a rumor I had heard for years: Gene Roddenberry, creator of Star Trek, wanted the original starship Enterprise moving silently through space. However, pressure from network executives forced him to add the familiar rumble and the "whoosh" as it flew past. In the later seasons, though, he removed the rumble. The "whoosh" in the opening credits stayed, though, probably (I'm guessing) because it would have cost too much to change the sequence. I guess the budget for space travel is tight even 200 years in the future.
There is a situation in which sound can propagate across space, when sound waves travel through an interstellar gas cloud. Even though they look thick and puffy, like the clouds after which they are named, a typical nebula (Latin for "cloud") is really not much more substantial than a vacuum. The atoms in the vast cloud are pretty far apart, but even a few atoms per cubic centimeter adds up when you're talking about a nebula trillions of kilometers thick. These atoms can indeed bump into each other, allowing sound to travel through the cloud.
Most processes that create "sound" in these nebulae, though, are pretty violent, such as when two clouds smash into each other or when a wind from a nearby star traveling at several kilometers per second slams into the nebula and compresses the gas. These processes generally try to push the gas around much faster than the nebula can react; the atoms of gas "communicate" with each other at the local speed of sound. If some atom is sitting around minding its own business and another one comes along moving faster than sound, the first atom is surprised by it. It's literally shocked: it didn't know what was coming. When this happens to a lot of material it's called a shock wave.
Shock waves are common in nebulae. They compress the gas into beautiful sheets and filaments, which we can "ooohh" and "ahhh" at from our nice comfortable planet safely located a few hundred light-years away. I imagine property values near the Orion Nebula are at a premium. The view is unparalleled, and if you choose your site correctly the ghostly whispers of swept-up atoms will remain unheard.
2. . . . of a dense asteroid field ...
Ever heard the term "asteroid swarm"? Well, it's more like an "asteroid vacuum." In our solar system the vast majority of asteroids are located in a region between Mars and Jupiter. The total amount of area defined by the circles of their two orbits is about one-quintillion (1018) square kilometers. That's a lot of room! Astronomer Dan Durda puts it this way: imagine a scale model of the solar system where the Sun is a largish beach ball a meter (1 yard) across. The Earth would be a marble 1 centimeter (1/2 inch) in size located about 100 meters (roughly the length of a football field) from the Sun. Mars would be a pea about 150 meters away from the Sun, and Jupiter, the size of a softball, about 500 meters out.
If you collected all the asteroids in the main belt and balled them up, they would be in toto about the size of a grain of sand. Now imagine crushing that grain of sand into millions of pieces and strewing it over the hundreds of thousands of square meters between Mars and Jupiter in the model. See the problem? You could tool around out there for months and never see an asteroid, let alone two.
In The Empire Strikes Back Han Solo has to do some pretty tricky maneuvering in an asteroid field to avoid being turned into Smuggler Paste by the Imperial starships. Those rocks were pretty big, too, dwarfing the Millennium Falcon. Let's say the average asteroid in that swarm was 100 meters across, and the average distance between them was 1 kilometer (0.6 miles)-we're being very generous here! Given the average density of rock (a couple of grams per cubic centimeter), that would give each asteroid a mass of about a trillion grams, or about a million tons. That in turn means the entire swarm, if it is the same size as our own asteroid belt, would have a mass of about 1030 grams. That's about a million times the mass of our own asteroid belt, or the combined mass of all the planets in our solar system. That's one big asteroid swarm. No wonder Solo could hide his ship there!
It's possible that in other solar systems, asteroid belts are bigger. We have just started detecting planets orbiting other stars, and these exosolar systems are very different than our own; we have just the beginnings of a cosmic diversity program. We don't have the technology yet to know what the asteroid belts in these other systems look like or if they even have asteroid belts. Still, a lot of movies use a very dense asteroid "storm" to advance the plot. (The original TV series Lost in Space used one to throw the Jupiter 2 off course, and Star Trek used it as an excuse to damage a vessel so that it could be rescued by Kirk and crew.) How many of them can there be? I suppose we'll just have to wait and see.
3. . . . banks hard to the left ...
Once again we run into a lack of air up there. We moribund humans are conditioned to expect airplanes to bank as they make turns. Tilting the wings of the plane helps redirect the thrust to the side, turning the plane. But note what is doing the pushing: air. Need I say it? No air in space.
To make a turn in space, you need to fire a rocket in the opposite direction that you want to turn. Need to escape to port? Thrust starboard. Actually, banking makes the situation even worse: it presents a broader target to a pursuing enemy. Keeping the wings level means less ship to aim at. Speaking of which, why do so many movies have spaceships with wings in the first place?
To be fair, I'll note that banking has one advantage. When a car makes a turn to the left, the passengers feel a force to the right. That's called the centripetal force, and it would work on a spaceship, too. Extensive tests by the Air Force have shown that the human body reacts poorly to high levels of acceleration. A seated pilot accelerated upward experiences forces draining blood away from the brain, blacking him out. If he's accelerated downward, blood is forced into the head, an unpleasant feeling as well. The best way for the body to take a force is straight back, pushing the pilot into his or her seat. So, if a pilot flying a spaceship banks during a turn, the centripetal force is directed back, pushing the pilot harder against the seat. Blacking out during a space battle is not such a hot idea, so maybe there's some truth to banking in space after all.
One other thing: if the spaceship has artificial gravity, then the computer should be able to account for and counteract any centripetal force. So if you see a movie in which Our Heroes have gravity onboard and still bank, you know that you're seeing more bad astronomy.
4. . . . and dodges laser beams from the Dreaded Enemy ...
If screenwriters have a hard time with the speed of sound, imagine how difficult it must be for them to work with the speed of light. Perhaps you've heard the phrase "300,000 kilometers (186,000 miles) per second: not only a good idea, it's THE LAW!" They aren't kidding. According to everything we understand about physics today, nothing can travel faster than light. Now I accept that someday, perhaps, we may find a way around that limit. No one wants to do that more than astronomers: they would give up their biggest grant to climb aboard a spaceship and zip around the Galaxy. To be able to actually see a planetary nebula from up close, or to watch the final seconds as two madly whirling neutron stars coalesce in an Einsteinian dance of mutual gravitation: that's why we went into astronomy in the first place! But right now, today, we know of no way to travel or even to transmit information faster than light.
Therein lies the problem. Laser beams travel at the speed of light, so there is literally no way to tell that one is headed your way. There's more: out in space, you can't see lasers at all. A laser is a tightly focused beam of light, and that means all the photons are headed in one direction. They go forward, not sideways, so you can't see the beam. It's just like using a flashlight in clear air: you can't see the beam, you only see the spot of light when it hits a wall. If you see the beam, it's because stuff in the air like particles of dust, haze, or water droplets is scattering the photons in the beam sideways. In laser demonstrations on TV you can see the beam because the person running the demo has put something in the air to scatter the beam. My favorite was always chalk dust, but then I like banging erasers together. Anyway, if you're in a laser battle in your spaceship, you really won't see the enemy shot until it hits you. Poof! You're space vapor (ironically, a second shot fired would get lit up by all the dust from your exploding ship). Sorry, but dodging a laser is like trying to avoid taxes. You can try, but they'll catch up to you eventually. And unlike lasers, the IRS won't be beaming when it finds you ...
5. . . . who have come from a distant galaxy ...
Even the awesome speed of light can be pitifully dwarfed by the distances between stars. The nearest stars are years away at light speed, and the farthest stars you can see with your naked eye are hundreds or even thousands of light-years away. The Milky Way Galaxy is an unimaginably immense wheel of hundreds of billions of stars, over one-hundred-thousand light-years across-
-which in turn is dwarfed by the distance to the Andromeda galaxy, the nearest spiral galaxy like our own. M31, as astronomers in the know call it, is nearly three million light-years away. Light that left M31 as you look at it in your spring sky started its journey when Australopithecus afarensis was the most intelligent primate on the planet. And that's the nearest spiral. Most galaxies you can see with a modest telescope are a hundred-million light-years away or more.
Now, doesn't it seem faintly ridiculous for aliens to travel from some distant galaxy to the Earth? After all, the distances are pretty fierce, and they have many, many stars to plunder and pillage in their own backyard. Science-fiction movie writers tend to confuse "galaxy," "universe," and "star" quite a bit. The 1997 NBC madefor-TV movie, Invasion, was advertised as having aliens travel "over a million miles" to get here. Ironically, ad writers wanted that distance to sound huge, but consider this: the Moon is only a quarter of a million miles away, and the nearest planet about 25 million miles away. The nearest star to the Sun, Alpha Centauri, is 26 million-million miles away. It sounds like they grossly underestimated the size of the gas tanks on the alien ships.
6. . . . to steal all of Earth's precious water ...
This is my personal favorite. It was used in the 1980s TV movie, V. and countless other pulp sci-fi movies. This may have started in the late 1800s, when astronomer Percival Lowell thought he saw canals on Mars and concluded that the planet was drying up. Obviously, an advanced race was trying to save itself via irrigation. Unfortunately, what he really saw were faint features on Mars that his all-too-human brain tried to connect up in his imagination. There are no canals on Mars.
On the face of it, that aliens want our water seems plausible: look at all the water we have on Earth. Our planet is three-quarters covered in it! Desperate for water, what would our proposed aliens do? After looking toward our blue world with envious eyes and parched tongues (or whatever they had in their mouths, if they even had mouths), would they come all the way in to the center of the solar system, using up huge amounts of energy to get in and out of the steepest part of the Sun's and Earth's gravity wells, to suck up water in its very inconvenient liquid form?
No way. Water is everywhere in the solar system. Every outer moon in our system has quite a bit of frozen water. Saturn's rings are mostly composed of water ice. And if that's no good, there are trillions of chunks of ice prowling the cold vastness of the Oort cloud, the cometary halo of the Sun that is almost a light-year across. Why expend all that energy to get to Earth when you can mine the ice out of all those comets, a trillion kilometers from the heat and fierce gravity of the Sun? And ice is a very convenient form of water. It may take up slightly more room than liquid water, but it doesn't need a container. Simply chisel it into the shape you want, strap it to the outside of your ship, and off you go.
Of course, in V, besides stealing our water, the aliens also came here to eat us. In that case, they did have a good reason to come to the Earth. Tough luck for us. Still, if I were some ravenous alien with a taste for human flesh, I'd simply gather up a bunch of cells and clone them to my heart's (or whatever) content. Why travel hundreds of light-years to eat out when staying home is so much easier?
7. The Dreaded Enemy tries to escape Earth's gravity, but is caught like a fly in amber.
How many times have you heard the phrase, "escape from Earth's gravity"? Technically it's impossible. According to Einstein, the mass of the Earth bends space, and the farther away you get, the less space gets bent. We feel that bending as gravity. But even Albert would agree with Isaac Newton that in general terms, the force you feel from gravity weakens proportionally as the square of the distance. So, if you double your distance from the Earth, you feel a force one-quarter what you did before. If you go 10 times farther away, that force drops by a factor of 100. You'll note that gravity drops off fast, but not infinitely fast. In other words, even if you go a billion times farther away, you will still feel some (extraordinarily small) force. Gravity never goes away, and if you forget that for an instant you'll be sorry. Toddlers tend to learn it pretty quickly.
So if gravity is always around, it's not like you are floating carefree one instant and suddenly feeling a strong gravitational force the next. It's a gradual change as you approach an object. Star Trek would sometimes have the Enterprise lurch as it approached a planet and gotten "stuck" in the gravity, sending hapless crewmembers flying from their stations. Luckily, the universe doesn't behave that way.
You'd think after the second or third time that happened, someone down in the Enterprise's engineering section would have whipped up some seat belts.
8. As stars flash by .. .
When you're talking real estate in outer space, it's not location, location, location but scale, scale, scale. Planets are pretty far apart, but stars are really, really, really far apart. The nearest star to the Earth (besides the Sun) is about 40 trillion kilometers (25 trillion miles) away. Even distant Pluto is 8,000 times closer than that. You can go all the way across our solar system and, to the naked eye, the stars will not have appeared to move at all. The constellations will look the same on any planet in the solar system.
But actually, if you go to Pluto, for instance, the stars will appear to move a tiny but measurable amount. The European satellite Hipparcos was launched specifically to measure the change in the apparent position of stars as it orbits the Earth. By making exact position measurements, you can determine the distance to nearby stars. Hipparcos has already revolutionized our ideas on the size of the universe simply by finding that some stars are about 10 percent farther away than previously thought. The downside of this, of course, is that the commute for the aliens is longer.
I was once fooled by someone asking what was the nearest star to the Earth. "Proxima Centauri!" I piped up, but of course the real answer is the Sun. In the movie, Star Trek IV The Voyage Home, the Enterprise and crew need to warp past the Sun to go back in time. There are two problems with this scene. One is that you can actually see stars moving past them as they travel to the Sun; there aren't any. Second, at the speed of light, the Sun is a mere 8 minutes away. At warp 9 they would have zipped past the Sun in less than a second. That would have made for a short scene.
9. . . . Our Hero gets a lock on them and fires! A huge ball of expanding light erupts past us, accompanied by an even faster expanding ring of material as the Dreaded Enemy's engines explode.
Explosions in space are tricky. Stuck here as we are on the Earth, we expect to see a mushroom cloud caused by the superheated air in the explosion rising rapidly, accompanied by an expanding circle of compressed air formed by the shock wave as it moves along the ground.
The lack of air in space strikes once again. In the vacuum of space there is nothing to get compressed. The expanding shell of light that is the trademark of most science-fiction explosions is just another way to make viewers feel more at home. The debris itself expands more slowly; pieces fly out in all directions. Since there is no up or down in space, the explosion will tend to expand in a sphere. The debris will no doubt be very hot, so we might actually see what looks like sparks exploding outward, but that's about it.
Of course, it's a lot more dramatic to have nifty things happen during an explosion. The quickly expanding shell of light looks really cool, if implausible. Sometimes, though, it makes some sense. In the movie, 2010: the Year We Make Contact, Jupiter is compressed by advanced alien machinery until it is dense enough to sustain nuclear fusion in its core. The core ignites, sending a huge shock wave through the outer atmosphere. This would get blown off and be seen as an expanding shell of light. That was relatively accurate and fun to watch, besides.
A special effect tacked on in recent movies is the expanding ring of material seen in explosions. This started with Star Trek VI: The Undiscovered Country, when Praxis, the Klingon moon, exploded. The expanding ring that results is for my money the most dramatic effect ever filmed. I also have to give this scene the benefit of a doubt. The expanding ring we see during a large explosion on Earth is shaped by the ground itself. You can think of it as part of the explosion trying to move straight down but being deflected sideways by the ground. In space, you wouldn't get this ring, you'd get a sphere. But the explosion in Star Trek VI was not a simple one; it's possible the expansion was distorted by the shape of the moon. A flat ring is unlikely but not impossible.
In the special edition of Star Wars: A New Hope, released in 1997, the Death Star explosion at the end (hope I didn't spoil it for you) also features an expanding ring. Once again, I'll defend the effect: explosions, like electricity, seek the path of least resistance. Remember, the Death Star had a trench going around its equator. An explosion eating its way out from the center would hit that trench first and suddenly find all resistance to expansion gone. Kaboom! Expanding ring.
We see expanding rings in real astronomy as well. The ring around Supernova 1987a is a prime example. It existed for thousands of years before the star exploded, the result of expanding gas being shaped by gas already in existence around the star. Even though not technically caused by an explosion, it shows that sometimes art imitates nature.
10. Yelling joyously, Our Hero flies across the disk of the full Moon, with the Sun just beyond.
The phases of the Moon always seem to baffle movie makers. The phase is the outcome of simple geometry: the Moon is a sphere that reflects sunlight. If the Sun is behind us, we see the entire hemisphere of the Moon facing us lit up, and we call it a full Moon. If the Sun is on the other side of the Moon, we see only the dark hemisphere and we call it a new Moon. If the Sun is off at 90 degrees from the Moon, we see one-half of the near hemisphere lit, and we call it half full or, confusingly, a quarter moon, since this happens one-quarter of the way through the Moon's phase cycle. This is explained in detail in chapter 6, "Phase the Nation."
In the 1976 British television program Space: 1999, for example, the Moon is blasted from Earth's orbit by a bizarre explosion (which in itself would be bad astronomy but is later explained in the series to have involved an alien influence). In the show, we would always see the Moon traveling through deep space in a nearly full phase. Just where was that light coming from? Of course, in deep space there is no light source, which would have made for a pretty boring shot of the Moon.
Even worse, in movies and a lot of children's books the Moon is sometimes depicted with a star between the horns of the crescent. That would mean a star is between the the Moon and the Earth. Better grab your suntan lotion!
Our fictionalized movie scene has some dreadful astronomy in it, and we haven't even touched on black holes, star birth, and what nebulae really look like. But what movies have good astronomy? Any astronomer will instantly reply: 2001: A Space Odyssey. In that movie, for example, the spaceship moves silently through space (a fact they evidently forgot when making the sequel 2010: the Year We Make Contact). There are countless other examples. An astronomer once told me that the only mistake in the movie is when one of the characters, on his way to the Moon on the PanAm shuttle, takes a drink from his meal and you can see the liquid in his straw go back down after he finishes sipping. Since there is no gravity on the shuttle, the liquid would stay drawn up in the straw. This is nit-picking at an almost unbelievable level, and I think we can forgive the director.
Surprisingly, the TV show The Simpsons commonly has correct astronomy. There is an episode in which a comet threatens to collide with the Earth. The comet is shown being discovered by an amateur (our antihero, Bart). Most comets are indeed discovered by amateurs and not professionals. Bart then calls the observatory to confirm it, which is also the correct procedure (he even gives coordinates using the correct jargon). When it enters the Earth's atmosphere, the comet is disintegrated by all the smog in the air of the Simpsons' overdeveloped city. That part can be chalked up to comedic license, but then comes an extraordinary scene: The part of the comet that gets through the pollution is only about the size of "a Chihuahua's head," and when it hits the ground, Bart simply picks it up and puts it in his pocket. As we saw in chapter 15, contrary to common belief, most of the time a small meteorite will not be burning hot when it hits the ground. The rock (or metal) is initially moving very rapidly through the upper atmosphere, which will melt the outer layers, but friction very quickly slows the rock down. The melted parts get blown off and the remaining chunk will only be warm to the touch after impact. In this episode of The Simpsons, they imply that the comet chunk is hot but not too hot to pick up. That's close enough for me.
After the original version of this chapter appeared in Astronomy magazine in April 1998, I received a letter from a young girl accusing me of ruining science-fiction movies for her. I have also received the occasional e-mail from my web site, where I review specific movies like Armageddon, Deep Impact, and Contact, telling me to either "get a life" or "learn how to just enjoy a movie." On the other hand, I get a hundred times as much e-mail agreeing with my reviews. Still, dissenters have a valid point. Do I really hate Hollywood movies?
Armageddon notwithstanding, no I don't. I like science fiction! I still see every sci-fi movie that comes out. When I was a kid I saw just about every science fiction movie ever made. I ate up every frame of rocket ships, alien monsters, evil goo, and extraterrestrial planets, no matter how ridiculous or just plain dumb the plot.
So what's the harm? You may be surprised to know that I think it is minimal. Although bad science in movies does reinforce the public's misunderstanding of science, the fact that science fiction does so well at the box office is heartening. Most of the topten movies of all time are science fiction, showing that people really do like science in movies, even if it's, well, bad. I would of course prefer that movies portray science (and scientists!) more realistically. Sometimes science must be sacrificed for the plot, but many times, maybe even most of the time, correct science could actually improve the plot. Thoughtful movies do well, too, like Contact and, of course, 2001, now a classic of science fiction.
If movies spark an interest in science in some kid somewhere, then that's wonderful. Even a bad movie might make a kid stop and look at a science book in the library, or want to read more about lasers, or asteroids, or the real possibility of alien life. Who knows where that might lead?
For me, it led to a life of astronomy. I can only hope that even bad astronomy, somehow, can spark good astronomy somewhere.