Space is a big-ass place.
It’s so damn big, in fact, that any relatively decent distance surpasses the capacities of our usual Earthling measurement units. So to avoid saying 588 x 10^8 miles or 9’460’730’472’580’800 meters, we just say 1 ly. Pretty cool, ha.
There are three units of measurement that are predominately used in astronomy, and thus also in science-fiction:
Astronomical units (AU)
An astronomical unit is the average distance between Earth and the sun. And isn’t it obvious we’d take our own planet as a point of reference to measure the galaxy, since it’s by far the most important flying rock out there? What? It is. IT IS. It’s… home. *watery eyes*
The Earth revolves around the sun in an elliptical orbit, which means it’s sometimes closer, sometimes farther away from the sun. Originally, one AU was defined as the length of the semi-major axis of Earth’s orbit, but for simplification purposes (tongue-in-cheek), a bunch of astrophysicists and mathematicians decided Earth’s orbit isn’t ‘perfect’ enough so they replaced our planet with a particle with infinitesimal mass and thus near to zero perturbations in its perfect elliptical orbit, and calculated the average distance between it and the Sun. And ta-da! you get an AU. Which is about 149’597’870’700 meters. *ouch*
AUs are usually used to measure distances within a planetary system. It’s easiest to imagine the position of a planet, asteroid belt or space-ship in a star system if you can compare it to that between Earth and the sun. I guess.
A lot bigger than AUs, are light-years. Much more practical for measuring interstellar distances. Otherwise we’d end up with big numbers again, and that’s migraine-inducing for everyone.
A light-year is the distance traveled by light in a vacuum in a year. That’s roughly 9.5 trillion kilometers, or 6 trillion miles. My head just exploded trying to visualize those numbers. See the angry looking cartoon eyes in the picture above? THAT’s how much I hate having to use gigantic numbers. Don’t get me wrong, I like math and physics, but we’re not that close, if you know what I’m sayin’. So no big numbers for me, thanks.
The light-year is the most common used measurement unit in science-fiction precisely because it’s that big. It’s also relatively easy to visualize, even though that visualization is mostly wonky. At least it feels right. You can feel a light-year. It’s a palpable, beefy distance (shut up).
To give you a sense of size, the nearest stars to our good old sun are Alpha and Proxima Centauri, and they’re 4.395 light-years away. That’d be 4.395 x 9’460’730’472’580.8 km = HEADSPLOSION
A parsec is even bigger than a light-year. In fact, it’s about 3.26 light-years. An ugly number, and it ain’t pretty to calculate, but what can you do, eh… (Except get a degree in advanced astrophysics and then write a paper on interstellar distances and change global measuring conventions. Should be easy enough.)
A parsec is the length of the long leg of a right triangle, whose short leg is 1 AU when the angle between the Sun and the Earth, as seen from outside, is 1 arcsecond (Or 0.000277777778 degrees. And here we have that awesome number-escaping again. Seems even mathematicians hate long numbers!).
To reuse our example, the distance between the sun and our nearest neighbors, Alpha & Proxima Centauri, would then be 1.347 parsecs.
Oh, and the word parsec comes from paralax of an arcsecond which sounds even more science-fictiony than light-year, time dilation, or plasma manifold malfunction.
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This post is part of the A to Z Blogging Challenge, April 2014.
In 2012, my D post was — Description – The Devil’s In The Details