I am a big fan of NASA’s Visible Earth image showing the world at night. The image above from Oct 2012 is actually a composite of cloud-free, nighttime satellite images stitched together to show one clear view of the earth at night. The images are captured by Suomi National Polar-orbiting Partnership satellite. The lights show major metropolitan areas — but it would be a mistake to think that the lights are equal to population distribution. For example, there are a lot of people living in Africa but you would not know that from the map above. Really, the lights show industrialized society.
If we zoom into North America (the image above is from an earlier photo from NASA), you can start to pick out major metropolitan areas. In fact, you can make a game out of it. New York City, Philadelphia and Baltimore all run together and are pretty easy to spot. But can you pick out Houston and Dallas or Denver and Salt Lake City, or St. Louis and Indianapolis?
With all this light pouring out into space, you can start to understand why it is difficult to see the night sky if you live in one of these major metropolitan areas. Anyone looking up at night will do better to travel into the country where the sky is clearer and the stars shine brighter. If you want to learn how you can help curb light pollution, visit The International Dark-Sky Association — a non-profit organization fighting to preserve the darkness of night.