Wednesday, October 22, 2008

A pretty picture

Today's Astronomy Picture of the Day is quite stunning:
The spiral galaxy NGC 7331
Image Credit: Vicent Peris, Gilles Bergond, Calar Alto Observatory, APOD

If you were to put your eye up to a big telescope and look at this spiral galaxy, this is not what you would see. This image has been heavily processed to bring out details and subtle colors; the process is described here.

Most color astronomy pictures you see on the web or in print have been processed quite heavily. Some people don't like that; they want what your eyeball would see at the telescope. In that case, here you go:

Sketch of NGC 7331
Image Credit: Wes Stone

Wes Stone's sketch is very impressive (most people would probably just see an oval blob), but you still miss out on a lot of the details that the processed image can get you. The fact is, the reason we astronomers use cameras and computers to process images are to bring out details that the eye, an imperfect light-collecting device, would normally miss. The colors in the first image are giving us a lot of information-- that the big galaxy is making new stars, that the other galaxies are much further away, and even some details about the stars in our own Milky Way that appear in the same picture. Your eye alone would never see these subtle colors, only a faint, ghostly white, and so you would not be able to ever learn what is going on in each of the "island universes" (galaxies) in the pictures.

The image processing that we do to make pretty pictures is not done to fool anyone, or to take away the "naturalness" of an image (if any picture made by sticking a digital camera on the back of a heavy piece of machinery is "natural"). Rather, it is to bring out the true beauty of stars and planets and galaxies, to enable each of us to look on worlds that our eyes alone would never be able to reveal.

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