Great link.
For those of you that have google earth installed, it only takes about 3 minutes to overlay this picture onto google earth, and you can then switch the overlay on or off in the sidebar at your pleasure. Simply:
*Save the picture you want to overlay from the first thread in this post
*Open google earth and move the map over Australia/New Zealand, whichever is relevant for the overlay map you are pasting
*Click 'Add > Image overlay'
*In name field write 'Light Pollution', and click browse at the end of the 'Link' field. Browse to the .jpg file of the light pollution that you saved in step 1. Move the 'Transperancy' Bar to halfway between clear and opaque.
*To line up the picture, you can move the overlay by dragging it in the centre green box on your google map. You can adjust the size and line it up properly by dragging the four corners. Adjust it so that it lines up nicely.
Refer to this image for what it should look like:
http://img180.imageshack.us/img180/8421/step1rw0.jpg
*Click OK and Voala!
For those that don't have google earth installed it can be downloaded for free from
http://earth.google.com/
Here is a screenshot of what it looks linke now when I zoom into Sydney. My house is in the middle of the red zone
http://img218.imageshack.us/img218/9074/step2ur8.jpg