One of the things that’s got to be frustrating about astronomy is just how little astronomers have to work with. They can’t walk up to a star and stick a thermometer in it or weigh it on a scale. They can’t even go around a star and look at it from a different angle. They can’t go anywhere the Earth doesn’t want to go, and the instruments on space probes don’t go very far or very fast. They can’t collect matter samples from distant stars and planets because matter, traveling at less than the speed of light, hasn’t had nearly enough time to get here. That leaves them with pretty much nothing but light. Okay, electromagnetic radiation of all frequencies, but it’s still just photons. Basically, all they can do is stand in one spot and watch.
And what’s amazing is that they keep coming up with ways of teasing unbelievable amounts of information out of the light that reaches us. They can see what its frequency distribution is, what spectral lines have been added or removed, which tells them what atoms and molecules are involved, and also whether that matter’s moving toward or away from us, and how fast. And a million other bits of information beyond that.
To illustrate, Sean Carroll (no, not
Sean Carroll the biologist,
Sean Carroll the cosmologist)
explains how scientists recently demonstrated that dark matter really exists.
Go read
the whole thing, because it’s clearly explained, with cool pictures.
In a nutshell, though, it’s an example of what I was talking about above, of teasing out all sorts of information out of light.
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