That is the question posed and answered by Thierry Cohen's "Darkened Cities" photography project. By merging two sets of photos he recreates what would be the view from the city, if it were not producing light pollution.
The process involves taking a photograph in the countryside, verified to be at the same latitude as the city shot and using an identical camera angle in order to record the "same" sky a few hours earlier or later. Through this technique Cohen is able to show the "real" sky, the one you should be seeing if the city was not so big and wasn't emitting so much light.
The resulting photos are a powerful warning that as more and more of the world's population becomes urban, and as we lose our connection with the natural world, we become oblivious to our impact. At the same time they are a beautiful reminder of the context to which our cities, and humanity in general, belong:
|São Paulo, Minhocão|
|São Paulo, Paulista Avenue|
|Rio de Janeiro|