About the Image

1. This is one WFCAM "tile" - four separate "pawprint" images, stitched together (if you look closely you can see at least one of the "joins". So the full image is about 16,000 pixels on a side, each pixel being a 0.2 by 0.2 arcsecond square.
2. Blue stars in this image are relatively in the foreground (though mostly many thousands of light years away); red stars (of which you'll see many more in the bottom left of the image and in the dark-cloud regions) are further off and/or more extinguished by intervening dust clouds.
3. The Galactic Centre is around 25,000 light years from Earth, which means that the light you are seeing from it has been travelling 25,000 years to get to us.
   
4. Almost nothing in this image is seen in visible light (that's one of the beauties of the infrared - we see through the dust so the Galaxy becomes transparent). If it were not for the intervening interstellar dust, the centre of the Galaxy would shine as brightly as the full moon.
   
5. Every star in this image has been catalogued - brightness, colour, etc. so the astronomical community can do real quantitative science. 
6. The UKIDSS galactic plane survey (from which the data were taken) comprises a couple of thousand fields of this size, and it's now catalogued well over a billion stars...