When you can barely see flecks of starlight shining upon a city - where the lights never turn off, where the night sky is perpetually shrouded in a haze of murky light - you're left with the thought: what would happen if there were a power outage, just for five minutes? What would the heavens reveal?
Photographer Thierry Cohen  in his photo series Darkened Cities  answers that very question, with swirls of stars shining high above nine of our major cities: Shanghai, Hong Kong, New York, Rio de Janeiro and more.
To create these photo composites, Cohen travels to another place in the world on the same latitude, where the sky is clear and there is little light on earth to interfere with the starlight. For Hong Kong's cityscape, the sky is that of the Western Sahara desert that's more than 12,000 kilometres away; for Paris it's northern Montana; and New York gets the stars above the Nevada desert.
While the images are beautiful, "these skies are an indictment and a lament", writes Francis Hodgson former head of the photographs department of the auction house Sotheby's in an essay on the series.  "These are the skies that we don't see."
For all you globetrotters, his work will be on show in March at the Danziger gallery  in New York.
Maybe we can take this as incentive to turn off our lights for Earth Hour 2013 , which falls on March 23, starting at 8.30pm. See what it was like last year at Earth Hour 2012, when 2.8 million people in the city switched off their lights for an hour :