Bad Astronomy: Misconceptions and Misuses Revealed, from ...

BAD ASTRONOMY GOES HOLLYWOOD 251
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