Reference Publications

A clean, well-lighted planet

Natural History, Sept, 1997 by Joe Rao

For astronomers, these are the best and the worst of times. Powerful telescopes and sophisticated accessories are available at moderate prices, and detailed celestial information is accessible at the flip of a page or the tap of a keyboard. But never have so many people lived under such muddy skies.

Light pollution is the cause. Light from street lamps, signs, and spotlights is blotting out our night skies. Under the darkest skies, some 2,500 stars are visible to the naked eye. But in suburbs only about 300 may be seen; on a clear night, city skywatchers may see a few dozen. Some people forgetting -- some may never know -- what a starry sky looks like.

At many North American observatories -- including Kitt Peak, near Tucson, and Mount Wilson, outside of Los Angeles -- the ever brighter light of encroaching cities has forced astronomers to permanently abandon some work -- such as the search for distant galaxies.

Excess light also interferes with ecological processes, throwing off the migratory and singing patterns of birds and causing deciduous trees to hold on to their leaves longer. The life cycles of sea turtles have also been affected; females may not come to a beach to lay eggs if it is too brightly lit, and newly hatched turtles are misdirected from their normal seaward migration and drawn toward the lights of nearby homes and towns.

Cities can save electricity, money, and the night sky by making more informed lighting choices, such as installing inexpensive shielding to direct light downward where it is needed. To learn how you can get light population reduced in your area, write to the International Dark-Sky Association at 3545 N. Stewart Avenue, Tucson, AZ 85716 or visit its Web site at http://www.Darksky.org/ida/ida_2/.>