TUCSON, Ariz. -- Halley's Comet will make its best once-in-a-lifetime appearance early next year but astronomers fear light pollution may ruin the show for urban skywatchers.
'They'll have to see it on TV, just like everything else,' said Dave Crawford, an astronomer at Kitt Peak National Observatory. His vantange point is a mountaintop in the Arizona desert.
Crawford said people will have to drive 20 to 30 miles outside of urban centers to get a view of the comet.
To keep the comet from going unnoticed in the cities, the Astronomical League, the largest astronomical organization in the world, has started the Dark Skies for Comet Halley campaign. The idea is to dim or turn off unessential outdoor lighting for a while on Halley's best viewing nights.
The comet was last seen in 1910, when Model T Fords chugged along dirt roads, William Taft was president, and no one had ever heard of light pollution.
On its elliptical path, Halley's swings around the sun every 76 years. Its reappearance was predicted by English astronomer Edmund Halley who died in 1742.
The Astroomical League is concerned about dazzling shopping center displays, high-intensity floodlights and even ordinary street lamps that may interfere with comet watching.
Don Archer, executive secretary of the League, said the group is using the comet to start a nationwide grass roots campaign against light pollution.
'This is a once-in-a-lifetime phenomenon,' he said. 'We're using this opportunity to bring the public attention to the problem of light pollution.'
Archer estimates that with the continuation of current lighting practices, there will be no difference between night and day skies in 20 years.
'Light pollution is a major problem with both the amateur and professional astronomer,' Archer said. 'What makes it worse is that most of the lighting is wasted.'
Archer said any light seen above 150 feet is not serving its purpose.
Astronomers have come up with a practical and economical solution - low-pressure sodium lighting. When properly shielded, this type of light - the kind with the warm amber glow -- is directed only to the ground and emits light on a color wavelength, which does not interfere with night-sky viewing.
Some cities have exchanged the traditional high-pressure sodium lights for the low-pressure ones to cut expensive municipal lighting costs.
By making the switch, San Jose, Calif., expects to save about $1.8 million in annual energy bills.
Low-pressure sodium lights installed in Tucson parking lots provide better lighting and delight motorists, Crawford said.
To protect their multimillion-dollar astronomy industry, many areas of southern Arizona have ordinances restricting night lighting after 10 p.m. and banning new installations of mercury vapor lamps, the kind with the harsh blue glare.
But many cities are unfamiliar with lighting drawbacks because they do not have observatories nearby. Those are the targets of the Dark Skies program.
Crawford said he thinks in many cities the campaign's promoters 'are going to have a tough time.'
He said many cities worry that lowering lighting would lead to increased crime on dark streets and alleys.
Archer said studies show 'crime goes on, whether you have lights or not.'
'Most criminals are afraid of the dark, too,' he said.
Despite the concerns, observations at Kitt Peak indicate the world may be in for a treat.
In September, visiting University of California at Berkeley astronomers Hyron Spinrad and Stanislov Djorgovski described Halley's Comet as 50 percent to 100 percent brighter than expected. That was at a distance of 576.6 million miles from the sun.
At that distance, Halley's icy core had started to melt, forming a bright veil around the comet's nucleus. The returning comet was first sighted from the Palomar, Calif., observatory in October 1982.
But scientists are wary of promising too much for Halley's. In fact, Ray L. Newburn, a leader of the International Halley Watch, says the upcoming appearance will be the 'worst viewing for the naked eye in the last 2,000 years.'
This is because the comet will be on the far side of the sun when it will be its brightest.
Fred Schaaf, an astronomer at the University of Arizona Steward Observatory, said many of his professional colleagues are gun-shy about viewing possibilities.
'Even a slight change in the path of the comet can make a big difference,' he said.
