From: Andy Soos, ENN
Published November 7, 2011 08:25 AM

The Lights of Really Distant Cities

Light pollution is not something to be terribly happy about. Researchers from Princeton and Harvard universities now suggest a seemingly more straightforward method to see who is out there by seeing who's left the light on. Edwin Turner, a professor in Princeton's Department of Astrophysical Sciences, and Avi Loeb, professor and chair of Harvard's Department of Astronomy, have reported a technique that could detect alien civilizations by the artificial light that would emanate from their cities. Turner and Loeb's work, which presents a mathematical algorithm to detect and observe this artificial light from Earth, has been submitted to the journal Astrobiology.

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"It's very unlikely that there are alien cities on the edge of our solar system, but the principle of science is to find a method to check," said Turner, who has focused on numerous topics in theoretical and observational astrophysics, including large-scale structure, dark matter, exoplanets and astrobiology. "Before Galileo, it was conventional wisdom that heavier objects fell faster than light objects, but he tested the belief and found they actually fall at the same rate. In the same respect, our method is a tool to at least check for traces of other civilizations within our solar system, even though the consensus is that they don't exist."

In other words science keeps on looking in any way it can.  

Loeb added, "Looking for alien cities would be a long shot, but wouldn't require extra resources. And if we succeed, it would change our perception of our place in the universe."

As with other methods to search for extraterrestrial intelligence, Turner and Loeb's concept relies on the assumption that aliens would use Earth-like technologies. Any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness, the researchers posit.

To spot a city on an exoplanet — one found outside our solar system — the city's light would have to be distinguished from the glare from the parent star. Loeb and Turner suggest looking at the change in light from a distant planet as it moves around its star.

As the planet orbits, it goes through phases similar to those of the moon. When it is in a dark phase, artificial light from the night side of the planet would be more visible from Earth than reflected light from the day side. So the total flux from a planet with city lighting would vary in a way that is measurably different from a planet that has no artificial lights.

Given that its orbit will be elliptical, the amount of reflected light will change with the distance from its star. But the amount of artificial light will remain constant. So the total flux from a planet with city street lighting will vary in a way that is measurably different from a planet that has no streetlights.

There's a caveat, however. "For this signature to be detectable, the night side needs to have an artiļ¬cial brightness comparable to the natural illumination of the day side," say Loeb and Turner. That seems rather unlikely given that Earth's night time illumination is some 100,000 times less its day time lighting.

Present day telescopes will not see far enough for this technique to work outside our solar system.  It would work within the solar system so that we could see a large alien city lit at night.  

Observing light pollution is one way but there can be other ways such as observing CFCs in the another planets atmosphere.  Such is very unlikely to be present except by artificial means such as another intelligence outside our own.  

For further information:  http://www.princeton.edu/main/news/archive/S32/04/37E56/index.xml?section=topstories,featured

Photo:   http://www.nasa.gov/multimedia/downloads/north-america-night.html

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