Monday, May 24, 2010

Light Pollution

We begin with the greatest impediment of all to observing the heavens in today’s world. Light pollution is excessive or misdirected artificial outdoor lighting. It does no one any good, and almost everyone considerable harm.

Glare in the eyes of motorists and homeowners greatly reduces traffic safety and interferes with crime prevention. Properly shielding lights can reduce or eliminate these problems. Light pollution also has adverse, sometimes fatal, effects on many birds, animals, and plants. Excessive lighting at night has even been found to reduce production of melatonin in the human body and lead to increased incidence of certain cancers, including breast cancer. Again, proper shielding of lights and otherwise judicious use of them can mitigate these problems.

One key component of light pollution is both the costliest of all and the one that affects stargazers the most. Skyglow is light that escapes upward to illuminate the air above cities and other light-pollution sources. It not only washes out city-dwellers’ views of the stars but even as much as dozens of miles away from a large city it can ruin a section of sky for a rural sky-watcher.

Sky-glow alone is costing the United States several billion dollars a year in wasted energy (millions of barrels of oil, millions of tons of coal). Yet sky-glow can be greatly reduced by simply using “full-cutoff” shielded lights. Indeed, scientists estimate that about three-quarters of all existing light pollution can be eliminated by the use of already existing technology and practices.

Doing so will not just save money, it will reduce the need for energy and thereby lessen the burning of fossil fuels and all the problems that come with them: air and water pollution, global warming, and the destruction of wildlife habitats that usually accompanies the building of power plants.
So how can you, an individual, help in the battle against light pollution? The first step is to become educated by reading up on the subject—preferably first at the Web site of the International Dark-Sky Association (IDA), IDA is a twenty-year-old organization that now has more than eleven thousand members from all over the world.
You can act globally by joining IDA and locally by learning from IDA how to encourage local government and businesses to address the problem.

What can you do to get darker skies tonight? Not much, of course, except when you are able to drive to a darker site.

Bortle Dark-Sky Scale:

The Bortle Dark-Sky Scale is a nine-level numeric scale that measures the night sky's and stars brightness seen by naked eye with stellar limiting magnitude, of a particular location.

John Bortle created this new scale of sky darkness which he published in the February 2001 issue of Sky and Telescope magazine to help amateur astronomers compare the darkness of observing sites. The scale ranges from Class 1, the darkest skies available on Earth, through Class 9, inner-city skies.

The two images below summarizes Bortle's descriptions of this classes:

The two Earth-at-night pictures below shows the massive grouping of city lights.

Above: Enhanced photo covering Europe, Middle East
and part of Africa, with night lights on.

Below are some images of major cities around the world, taken from space on very clear skies at night..

Cape Town - South Africa

Dubai - UAE

Florida - USA

Istanbul - Turkey

London - UK

Milan - Italy

 Montreal - Canada

Moscow - Russia

 Moscow - Russia

New Orleans - USA 

 San Francisco Bay - USA

 Sao Paulo - Brazil

Southern Italy

Tokyo - Japan

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