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

IDIOM’S DELIGHT 29
press my height. An Angstrom is a truly dinky unit: 100 million of
them would fit across a single centimeter. Angstroms are used to
measure the sizes of atoms and the wavelengths of light, and they
are too awkward to use for anything else.
The point is that you can make things easy on yourself if you
change your unit to something appropriate for the distances involved.
In astronomy there aren’t too many units that big! But
there is one that’s pretty convenient. Light! Light travels very fast,
so fast that no one could accurately measure its speed until the
nineteenth century. We now know it travels about 300,000 kilometers
every second. That’s a million times the speed of sound! No
wonder no one could measure it until recently.
So, astronomers use light itself as a big unit. It took the Apollo
astronauts 3 days to go to the Moon in their slowpoke capsule, but
it takes a beam of light just 1.3 seconds to zip through the same
trip. So we say the Moon is 1.3 light-seconds away. Light takes
8 minutes to reach the Sun; the Sun is 8 light-minutes away. Distant
Pluto is about 6 light-hours away.
A light-minute or -hour may be useful for solar system work,
but it’s small potatoes on the scale of our Galaxy. Light doesn’t
travel far enough in only one minute. For galactic work, you need
a light-year, the distance a beam of light travels in one year. It’s
equal to about 10 trillion kilometers, which is a long way. Proxima
Centauri is 4.2 light-years away; the light leaving a presidential
inauguration might not reach Proxima Centauri until after the president
leaves office at the end of the term!
The light-year is the standard yardstick of astronomers. The
problem is that pesky word “year.” If you’re not familiar with the
term, you might think it’s a time unit like an hour or a day. Worse,
since it’s an astronomical term, people think it’s a really long time,
like it’s a lot of years. It isn’t. It’s a distance.
That doesn’t stop its misuse. The phrase “light-years ahead” is
a common advertising slogan used to represent how advanced a
product is, as if it’s way ahead of its time.
I can picture some advertising executive meeting with his team,
telling them that saying their product is “years more advanced
than the competition” just doesn’t cut it. One member of the ad