If you're in Chicago, then you might want to head over to the Adler planetarium today, when they unveil an enormous 2.5 billion pixel mosaic of the Galaxy! It's composed of 800,000 separate Spitzer Space Telescope images (I mean, c'mon, holy Haleakala, eight hundred thousand images!) stitched together. The image was actually released last year, but the ginormous print version is premiering at Adler today.

The image above is one very tiny piece of the mosaic; it was originally about 6000 pixels across, and I shrunk it down by a factor of 10 to fit it here on the blog. And that is still only an eensy weensy piece of the whole thing! Here is a massively ensmallened version of the entire mosaic:

[Click to get a 2400 x 3000 version.] The images are in the infrared, well outside what the eye can see. The colors represent IR light at 3.6, 8, and 24 microns (depicted in the picture as blue, green, and red). Different objects emit at different wavelengths: warm dust is red, while nebulae forming stars are yellow. The diffuse green glow seen everywhere in the image is from complex organic molecules called PAHs, or polycyclic aromatic hydrocarbons. On Earth those are created when fossil fuels are burned; in space, they are byproducts of stellar birth and death. Not surprisingly, there is no single link to the whole survey. However, all the tiles of the mosaic are available for download at the link above. But be ye fairly warned, says I: each subimage is roughly 25,000 x 13,000 pixels! This sort of image is more than a stunt; big, splashy surveys like this give us a grand overview of the galaxy. Telescopes like Spitzer, Hubble, Chandra, and so on usually get very deep, very detailed images, but of only a tiny fraction of the sky. By taking all these images and stitching them together, we get an overview of the galaxy that can be used to do statistical searches, look for populations of objects, and perhaps most importantly, get context for objects to see what kind of environment they sit in. The full mosaic is a stunning 2 degrees high -- four times the size of the full Moon on the sky -- by 120 degrees. The Spitzer folks created a video (hosted by my bud Robert Hurt) to explain how it was done. Also, something this size is almost too big for astronomers to probe in detail. So grab yourself an image or two and surf around. See what you find! And if you are in Chicago, what are you waiting for? I've been to Adler many times, and it's one of my favorite planetaria. Go see the giant scale model solar system, and the massive chunk of meteorite from Meteor Crater, Arizona! It's a wonderful place, and you'll have a lot of fun.