Bad Astronomy. Misconceptions and Misuses Revealed, from Astrology to the Moon Landing 'Hoax'

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 exo-solar 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 made-for- 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