Monday, April 09, 2007

Calibrating

One of my goals in this blog is to talk about the daily life of astronomers.A lot of people have an idea that we sit by telescopes on mountains. Ah, if only life were that glamorous (and I'm not sure that living the life of a hermit on a mountain is glamorous). Most of our time is sent in front of the computer, scrutinizing plots and numbers, and rarely stepping back to look at the really fantastic objects we are working on.

But this week is even more un-glamorous than that. I am working on calibrating pictures of star fields. I want to know exactly how bright every star in my digital image is. It's fairly easy to measure how bright they are in comparison with each other, but I want to be able to compare these stars with stars across the sky. It's a little like using an old balance scale. You can compare how heavy different objects are by putting them on opposite sides of the scale. But if you want to know how heavy something is in pounds (or kilograms), you need a set of measured weights. And if you want to be precise, you have to make sure that those weights are in pristine condition -- any nicks or cuts in the weights mean that a tiny amount of matter is missing. And you have to trust those measured weights, and hope that they truly weigh what they claim to weigh.

Likewise, with measuring star brightnesses, we have to use stars of know brightness to put things on the same scale. And tiny things can mess up our measurements -- perhaps there are some very thin clouds covering parts of the sky -- these will make stars appear slightly fainter than they really are, and we may not see those clouds. Or maybe the star we are using as a standard brightness indicator hasn't been measured as well as we would like. Or any one of a multitude of problems.

This work is boring, tedious, tiring, and less fun than watching paint dry or grass grow. But it is a crucial part of our work, because we can draw wrong conclusions if we are off by even a few percent. I won't bore you daily with details of each day's work, as this may take a while.

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