[alnorth]

Today I was wondering how the hell we could know how far away stars are, and when I looked it up, the answer was pretty obvious. There's also a technique involving measuring brightness and color, but for most stars that aren't incredibly far away, we just use basic trigonometry. Measure the angle of a star, wait 6 months for the earth to be on the other side of the sun, measure the angle again, and do the math. Since we know the diameter of our orbit, thats all you really need.

The angle measurements obviously have to be extremely precise because we're talking about something that is ludicrously far away compared to our orbit. After about 400 light years we apparently lack the ability to measure the angle with enough precision to use the simpler trig method.