Astronomers study the light from objects in space to determine their size, location, and composition. They can do this most effectively when the only light entering their telescopic instruments comes from those targeted bodies. Increasingly, this is becoming more difficult to ensure, because lights from nearby cities can include some of the same elements that may be found in space-based targets, making the necessary separation and identification of light sources difficult.
Two main difficulties with non-targeted light sources
The first and most easily fixed problem is with street lights that are improperly aimed and covered. This is because “unshielded lights send their light in all directions,” and that includes straight up into the night skies. Common sense would allow one to conclude that the light thus wasted lighting the bottoms of clouds or aircraft also constitutes an unnecessary expenditure of precious energy.
If city governments are careful about their lighting purchases, the problem of unshielded fixtures can be somewhat abated. With enough planning and development in this area, nearby astronomical observatories can continue to function for decades, though they will not likely see any more truly dark skies except in the unwanted event of an electrical blackout.
Just as crucial as the aiming and proper hooding of street lamps is the consideration of what element is used to produce their light. If astronomers get their way, and in some cities, for a while, they have, cities will decide to use sodium vapor street lamps. Why?
Sodium vapor lamps, even in the presence of spectrometers, do not clutter the entire electromagnetic band with spikes, obscuring the spectra of intended targets such as stars and galaxies. “Mercury vapor lamps have an enormous number of these spectral lines in all parts of the spectrum, and interfere with astronomical observations from the infrared to the ultraviolet.”
Sodium vapor is available but often unused
Though mercury and sodium vapor street lamps are both widely available, it is distressing to note that city leaders occasionally have other matters on their minds, matters political, financial and practical. If they have someone on staff who is familiar with the problems of light pollution, particularly in areas where astronomical observatories are known to be situated, there is hope that they will gather the political will to decide for sodium vapor lighting instead of mercury. However, administrations change, and political will is not always on the side of science. Even in cities where proper lighting is in place, and the fixtures are aimed correctly, contracts slide to expiration and frantic purchasing agents can buy the wrong lighting sources.
The United States shares this problem with other countries
It is evident from a cursory review of the literature on this topic that light pollution causes concern to scientific communities in other countries, as well. “10. There are currently no world–class optical telescope facilities in the United Kingdom. Light pollution makes this impossible.” (House of Commons Science and Technology Committee, UK Parliament Report on Light Pollution, 2002-03, page 11.)
Proper lighting sources for city streets, sporting events, and industrial facilities are one approach to a small slice of the problem. Light pollution itself is symptomatic of the more important juxtaposition of humans and their technology with the natural world. If a world of more than seven billion persons can find practical, appropriate ways to continue working into the night, and do it without causing damage to the natural environment, a day may come when other groups in addition to astronomers will have reason for happiness. Until that day comes, each small victory will preserve a small part of the night sky and, not inconsequentially, some of the power that might otherwise have been wasted. It seems worth the effort.