Over time, humans have disrupted natural rhythms of night and day by creating artificial light. The night skies above cities are hundreds, if not thousands of times brighter than 200 years ago, but we have all become accustomed to the safety and security that streetlights bring to us in urban areas.
But is all of the artificial lighting of the modern world just too much?
Tucson Arizona is famous for its dark skies. Its three observatories attract astronomers from across the United States.
When the local government decided to upgrade its streetlights they made sure to consult with an astronomer. What they weren't expecting was that the astronomer, John Barantine, had his own agenda: he wanted to find out just how much of the light pollution in his town was down to street lighting and he was going to measure it from space.