"Seeing in the dark"

I got a great little email from Elizabeth Moody, an Outreach Educator for COSI on Wheels, a couple weeks ago, regarding astronomy and the non-visible parts of the electromagnetic spectrum (which is, you know, most of it). Our eyes are only sensitive to a small sliver of frequencies of light, so when we operate an x-ray or infrared telescope, how do they work and how do they make images that we can...see?

First it's important to note that no matter what kind of light it's observing, a telescope has two important jobs: it's a bucket to soak up as much light as possible, and a focuser to dump that light onto a sensor. The "sensor" is your eyeball if you're an old-timey professional astronomer or a modern-timey amateur astronomer. Usually nowadays the pros have gone all digital.

Think about what your eyeball does: it collects light - the iris - and dumps it onto a sensor - the retina. What gets sent to your brain is raw "data": how much of what frequencies of light and where that light came from. Lots of reds from the barnside, a good bit of blue above it, green below, etc. Your brain turns all that data into an "image", giving you a visual map of an idyllic farm scene.

So what if we have a telescope that collects x-rays? The sensor reads how much of what frequencies of light came from where, and tell it to a computer. It's just a bunch of numbers, and to make a picture some creativity is required. Maybe the high-energy x-rays should be colored purple-bluish, and the lower-energy ones we captured should be given a gentle soft red.

In the end, a computer paints a picture for us, but giving us the same kind of information our brains do with visible light. We can play the same game at any frequency, from radio to gamma-rays. In effect, modern telescopes make us all a Superman.