Units are nifty. Most non-science people are rather frustrated by them, but typically, it's a very nice, quick way to check equations to make sure they'll actually give you the sort of quantity you're looking for. After all, you don't want a distance coming out with seconds as the unit. Rather, you'd want something in meters, or parsecs, or furlongs, etc....
In astronomy, we tend to switch between units quite often. Meters are perfectly fine for describing diameters of planets, but aren't ideal for the size of solar systems. For that we use Astronomical Units (AU). Those work great on that scale, but fall short (har har) for sizes of galaxies. Lightyears or parsecs are much better there. For cosmological distances, we like megaparsecs.
Quite often in classes, professors like to make sure you're paying attention to your units and will give you something in a unit that needs to be converted to something else before it will cancel with the units of a particular universal constant. Most of us students that have been doing this for awhile realized that having to look up the conversion factor and do the conversion by hand gets tedious.
Fortunately, the great Google can do every unit conversion known to man. Need to know how many megaparsecs 245 AU is? Just type in "245 AU to megaparsec" and BAM! Google spits out your answer: "245 Astronomical Units = 1.18779352 × 10-9 megaParsec". Nifty. Now let's try to figure out what the hell the rest of this problem this professor is asking us actually means...
Pretty straightforward. But Google sure does know some weird conversions. I mean, who the hell asks for the "number of horns on a unicorn acre in tea spoons per light year"?
Monday, October 01, 2007
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