This is why astronomers build telescopes in the mountains of Chile

When it comes to enjoying the full-blown magnificence of a star-studded sky, or the peak of a spectacular meteor shower, the Moon (to borrow a phrase from astronomer Mike Brown) is your nemesis.

But if this map of light pollution in the United States is any indication, you might as well think of city lights as the Moon's evil, night-sky-ruining cronies.

If you ever hear an astronomer talking about "bright time" or "dark time," what they're actually referring to are the times of the month when the Moon is either full or new, respectively. (Times in-between are known as "grey time.") The dark time that a new moon provides is perfect for spotting especially faint or distant celestial bodies, but during bright time, you pretty much have to accept that visibility for these kinds of objects is going to suck.

This is why astronomers build telescopes in the mountains of Chile

There's not a whole lot astronomers can do to prevent the phases of the Moon from interfering with an otherwise perfect night of stargazing, but avoiding light pollution from cities is a different story. Take the picture up top, for example. The image is based on data published in a 2001 issue of Monthly Notices of Royal Astronomical Society, and shows the kind of light pollution you can expect to find on account of the urban glow emanating from various regions of the continental United States. [Click here for hi res]

Just transporting yourself from a region labeled in red or white to one marked blue or black can have a dramatic impact on your ability to make out objects in the night sky, as illustrated in the two photos featured here. The bottom photo was taken in Orem, Utah — a major metropolitan area with a population of around 400,000 people. The top photo, on the other hand, was photographed in Leamington — a rural Utah town, about 75 miles southwest of Orem, with a population of just 217 people.

Astronomers like to do the same thing, only instead of making a ninety-minute trip out of the city, they book a flight to somewhere like Chile, where they can use telescopes located high in the remote mountains of the Atacama desert to get some of the best views of the Universe our planet has to offer.

It's difficult to imagine what the skies might have looked like at a time when this map would have been entirely black. Much easier (and, in many ways, sadder) to envision, is how our ever-expanding cities will only continue to rob our skies of what little starlight they have left.

Top image by David Lorentz, based on data collected by P. Cinzano, F. Falchi (University of Padova), C. D. Elvidge (NOAA National Geophysical Data Center, Boulder). Copyright Royal Astronomical Society. Reproduced from the Monthly Notices of the RAS by permission of Blackwell Science, via the Light Pollution Atlas; photos of the Utah sky by Jeremy Stanley