Phil Plait has a great description of what you see in this stunning new picture of the center of the Milky Way galaxy, a mosaic comprised of images from the Hubble (visible light), Chandra (X-rays), and Spitzer (infrared) space telescopes.

There is so much going on in this image it’s hard to know where to start. But first… the Hubble images are in the near-infrared, with a wavelength a little more than twice what the eye can see (1.87 microns for those playing at home). That’s represented in the image as yellow. Spitzer contributed observations in four infrared wavelengths (3.6, 4.5, 5.8, and 8.0 microns), and those are depicted in red. Chandra sees X-rays which are normally written as units of energy, but to remain consistent with the other two images, they were at wavelengths of 0.0005, 0.00025, and 0.00016 microns, and are shown in blue.

What does all this mean? Different objects emit light at different characteristic wavelengths. Warm dust, for example, emits strongly in the infrared. Stars and warm gas emit visible and near-infrared light. Violently heated gas, affected by huge magnetic fields or shocked by colossal collisions glows in X-rays. So this image is a polychromatic view of the crowded downtown region of a bustling city: our galaxy.

Here’s the page at HubbleSite, where you can find high resolution images for desktop wallpaper: HubbleSite - NewsCenter - NASA’s Great Observatories Celebrate International Year of Astronomy (11/10/2009) - Release Images.

And here’s the combined image; hover over it to see a popup showing all three parts.