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Star struck! The International Year of Astronomy
POSTED 8 JANUARY 2009

Glare: Astronomer's archenemy

Astronomy has progressed in the 400 years since Galileo discovered the moons of Jupiter. To take one small example, star-folks no longer fret about house arrest. But the progress is mixed: Galileo did not worry that city lights would drown out the stars...

For eons, the sky has benefited navigators, inspired stories and myths, and sparked wonder: What were those innumerable lights in the celestial dome, anyway?

Combating light pollution is no small problem: This composite photo shows every metropolitan area in the world. When you look up, do you stare into glare?
Map of world studded with lights. Europe and United States are particularly bright
Data courtesy Marc Imhoff of NASA GSFC and Christopher Elvidge of NOAA NGDC. Image by Craig Mayhew and Robert Simmon, GSFC.

Ironically, even as astronomers are breaking barriers in time and distance, we are losing our view of the stars.

City people may know the Milky Way only from photographs, and some even think the sky is supposed to be red, says Matthew Bershady, a professor of astronomy at the University of Wisconsin-Madison. He points out that two of the most productive telescopes in history, Lick Observatory and Mt. Wilson, have been overwhelmed by California's abundant light pollution, and says the problem gets worse as astronomers chase ever-fainter targets. "In a lot of dark sky observations, you are basically looking for objects that are fainter than the night sky."

Near Tucson, Arizona, long an astronomical Mecca, light pollution is growing as the city expands, Bershady says, and is even coming from burgeoning Phoenix, 120 miles to the north.

City lights that emit a sharp band of radiation are easily filtered out at telescopes, Bershady says, but many city lights, including the popular high-pressure sodium lamps, emit a broad, diffuse type of light. Astronomers advocate low-pressure sodium lights, which emit a narrow spectrum, but their light "makes you look sallow, ghoulish," Bershady admits. Eventually, the lighting industry may invent lamps that are acceptable to astronomers and citizens alike.

Monochrome photo shows a flat desert, with distant mountains framed by a brilliant bow of stars
Photo: Dan Duriscoe, National Park ServiceNASA
In Death Valley, dark skies and dry air create a phenomenal starscape dominated by clouds of stars and dark lanes of dust in our home galaxy, the Milky Way.

Darkness at night?

The bright-sky problem "is probably going to get worse before it gets better," concedes Johanna Duffek, coordinator of local chapters for the International Dark Sky Association, yet part of the solution is rather basic: Lights that shine downward put light where it is needed, Duffek says, while lights that shine upward just illuminate the sky and annoy astronomers and other lemur-like lovers of unlit locations.

The night sky is so saturated with light that it looks pale blue
Photo: Courtesy International Dark Sky Association.
Washington D.C. at "night." If funding for astronomy is short, could that be because our overlords in Washington can hardly see the stars?

Because light pollution represents wasted energy, "the thing we really like to talk about is that the solutions are actually money savers," Duffek says. "Our mission is to preserve and protect the nighttime environment, but we are not a radical organization saying, 'Turn off all the lights.' We believe in working with municipalities and lighting designers to enact good quality outdoor ordinances, and working with manufacturer to produce fully shielded lights that send out no light above a 90° angle."

Functional outdoor lights shine toward the ground, cutting shadows and improving safety for pedestrians without sending glare toward drivers, Duffek says. "With fully shielded lighting, you not wasting energy to light the sky, so you can usually use a lower-wattage bulb."

Although IDA was founded by astronomers, most members want a dark sky for other reasons, Duffek says, such as protecting wildlife. Sea turtles hatchling try to find the sea by traveling away from the darker, landward horizon. If a road or parking lot is unnaturally bright, they may follow instinct, shuffle toward the light, and get squished. And animals that hunt at night have trouble dealing with the constant twilight created by ubiquitous electric lighting.

I heard it on the radio

For astronomers, the light pollution problem is not just about "light," but also about the longer electromagnetic radiation we call radio waves. Snezana Stanimirovic, a radio astronomer who studies interstellar gas, says radio-frequency interference is a constant concern, whether it comes from little gadgets like cellphones, TVs, computers and cameras, or jumbo sources like radar, radio and TV broadcasters, and communication satellites. "GPS [global positioning system] satellites are a whopping big signal compared to astronomical signals," she says, "and they can wipe out whole chunks of the spectrum."

Woman stands before metal dish, about 2 meters in diameter, that points skyward
Snezana Stanimirovic stands before her new radio telescope. Once hooked to the requisite electronics, this dish will read radio signals from clouds of interstellar gas.

Radio telescopes in West Virginia and Puerto Rico are surrounded by quiet zones where small radio sources, such as cell phones or microwave ovens, are prohibited from interfering with the radio astronomers. The Arecibo observatory in Puerto Rico has an agreement with the Puerto Rico National Guard to use a part of the radar spectrum that does not interfere with particular observations.

The International Telecommunications Union, which regulates radio signals, has established a quiet band forbidding any human-generated signals around the 21-centimeter wavelength of atomic hydrogen, which, as the most common atom in the universe, is crucial to radio astronomy.

However, as more sections of the electromagnetic spectrum are sold to communication companies, interference is likely to increase. For example, Earth now has about 4 billion cell-phones.

Radio astronomers are trying to invent software and equipment to eradicate interference, Stanimirovic says, and the task "becomes more important as receivers get more sensitive. New radiotelescopes will be looking for signals from around the time of the Big Bang. These are very weak, so the band needs to be very clear; even weak interference can destroy the observation."

A lot is clear in our astro-bibliography.
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Terry Devitt, editor; Nathan Hebert, project assistant; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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