“Before we devised artificial lights and atmospheric pollution and modern forms of nocturnal entertainment we watched the stars. There were practical calendar reasons of course but there was more to it than that. Even today the most jaded city dweller can be unexpectedly moved upon encountering a clear night sky studded with thousands of twinkling stars. When it happens to me after all these years it still takes my breath away.” -Carl Sagan
For all of human history, we’ve battled against the limitations of our bodies and the natural world. That’s led to the development of artificial lighting: from fire to modern electric and LED lights. Despite being able to see our surroundings much more clearly at all hours regardless of the Moon or the clouds, we’ve also lost something spectacular: the night skies themselves.
A composite image of the Earth at night, with data from 1994/1995. Image credit: Craig Mayhew and Robert Simmon, NASA GSFC, with data from Marc Imhoff of NASA GSFC and Christopher Elvidge of NOAA NGDC.
There are thousands of stars visible to the naked eye from a truly dark-sky location, yet such places are increasingly harder to come by. East of the Mississippi in the United States, they barely exist at all. From many urban locations, even bright, easily recognizable sights like the North Star or the Big Dipper are no longer visible.
What a digital camera (top) and the human eye (bottom) sees from dark sky locations rating a 4, 6 and 9 on the Bortle scale, respectively. Image credit: Tony Flanders of Cloudy Nights, via http://www.cloudynights.com/topic/306632-illustrated-with-real-images-bortle-scale/.