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 crew-members 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!
