Thursday, September 24, 2009

Lost in a web of stars

The day job is less busy now. In the inevitable letdown period, my attention has wandered skyward, to the Astronomy Picture of the Day. Along with the Galaxy Zoo and other random sites, the APOD largely satisfies my desire to learn a little astronomy without, um, actually going out and looking at the sky. Besides, I learn more this way, or at least I learn things that just looking up at the sky gives little hint of. That's why they have all those telescopes and high-tech instruments, after all.

For example, while you'll often see pretty posters of the Orion nebulae or the Trifid nebula, it's another thing entirely to see them in context and realize that, were our eyes sufficiently sensitive (and our surroundings sufficiently dark) even a clear, dark sky would be cloudy. And of course, Van Gogh's Sterrennacht springs to mind.

In the night sky most places we see very little beyond local stars. In major cities it can be hard to see even that much. This limited view reveals very little about the universe at large. Recent theories hold that the universe was born out of some sort of quantum foam and still reflects that structure. What are they talking about? If you zoom out far enough, it starts to make sense.

How can astronomers develop theories of how stars and galaxies form when the timescales involved are much, much longer than anyone's lifetime? They look at lots and lots and lots of stars and galaxies. On a clear, dark night the unaided eye can pick out a few thousand stars. Galaxies have stars by the billion, and there are plenty of galaxies. The Hubble Deep Field, for example, covers about two millionths of the night sky and comprises about 3,000 galaxies. Even the Galaxy Zoo's original million are only a small sample of what's out there.

From common experience, stars (except our sun, of course) are little pinpricks of light. Science tells us that's because they're mind-bogglingly far away. Only objects in the solar system are close enough to appear as anything more than points [well ... you have the Sun, the Moon, the Andromeda galaxy, the Magellanic clouds and the occasional comet ... but let's just agree that you'll see a lot more with a telescope, especially a big one or one in space --D.H. Dec 2015]. But with a good telescope, you can not only tell stars from points of light, you can not only see that stars are round, you can see one that isn't and pick out individual stars in a galaxy far, far away (well, actually a pretty close one by galactic standards).

With special equipment astronomers can see colors the eye can't, as in this lovely image of the Andromeda galaxy in ultraviolet (make sure your cursor isn't over the picture), or pick out otherwise hidden features and reveal the complexity of the processes at work in a nebula, or even show us what's right in front of our faces.

This is a really small sample of the APOD archive. Wander through it yourself and you'll find all kinds of wonders and not a few oddities. But beyond the pretty pictures, the real value lies in the descriptions, written by professional astronomers. It's one thing to read in a science article about this or that theory or process, quite another to see a principle illustrated by a real live picture from a real live observatory accompanied by a clear, concise paragraph rich in links to further pictures and other resources.

This is the kind of thing the web was made for. Certainly it's long been possible to subscribe to an astronomy magazine or go to the local library and get information of a similar quality, but the web enhances the experience considerably.

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