How light pollution affects the dark night skies

This image illustrates the Bortle scale, which measures the impact of light pollution on the dark skies at a given location. It shows, from left to right, the increase in the number of stars and night-sky objects visible in excellent dark sky conditions compared with cities. 

The illustration is a modification of an original photograph taken at ESO's Paranal Observatory in Chile, a place with excellent dark-sky conditions, perfect for astronomy.