(originally run February 26, 1999)
The nighttime skies were often clear and dark outside his home near the southern "edge" of Alamogordo, New Mexico, when this author was a young boy growing up. The easy accessibility of the wonders of the outside universe just outside his front door played a significant role in stimulating his interest in astronomy and space at that time, and was a significant factor in his decision to return to New Mexico many years later. In the dark skies around his mountain home it is easy for this author to share the beauty of the nighttime sky with his own sons and their friends.
Not everyone is quite so fortunate, however. Many of our country's -- and world's -- citizens live in major metropolitan areas, which are bathed in intense "light pollution" -- the washing out of the nighttime sky by excess light being sent upward and then being scattered off particles in the atmosphere. In the Los Angeles area, where this author lived prior to his return to New Mexico, it was often all but impossible to see anything but the brightest stars in the sky, and he usually found it necessary to drive extensive distances into the surrounding mountains in order to find any kind of dark skies. Unless they are fortunate enough to spend some time in an activity such as a rural summer camp, many of the children in such environments can grow to adulthood without ever experiencing the beauty of a clear dark night.
Such light pollution certainly plays havoc with astronomical observations. Some astronomical observatories, such as Mt. Wilson located in the San Gabriel Mountains just north of Los Angeles, have been rendered all but useless by the light pollution caused by encroaching metropolitan areas. For this reason many of the world's leading astronomical institutions have had to retreat to more and more remote locations, and even these are having to contend with unwanted light arising from sometimes rather distant cities.
While some might argue that this is the price we have to pay for civilization, in truth most of this light pollution is completely unnecessary. Much of it comes from unshielded lighting that is directed upward, where there is no use for it; out society literally wastes 1 1/2 billion dollars every year doing nothing but illuminating dust particles in the atmosphere. In many cases a simple shield placed around a light source will ensure that the light is directed downward, where it is needed, and prevent it from being directed upward, where it is wasted; the energy that is saved from being wasted will pay for the costs of the shielding many times over.
That such an approach can work has been ably demonstrated by Kitt Peak National Observatory in southern Arizona. Despite being located less than an hour's drive from downtown Tucson, light controls that have been enacted in that city have kept the skies at Kitt Peak dark, and this remains as one of the world's foremost astronomical institutions.
A potential new threat to our dark nighttime skies has recently emerged. In February 1993 cosmonauts aboard the Russian space station Mir deployed a 20-meter-wide (65 feet) circular disk of aluminized Kevlar which was given the name Znamya ("Banner"). For the next few minutes reflected sunlight was directed from Znamya toward nightime sections of central Europe, and although most of the "target" areas were clouded out, some residents of Belorussia apparently witnessed a brief flash from Znamya that equaled the light of the full moon as the reflected sunlight swept over them.
Earlier this month a new reflection experiment with a larger (25 meters, or 80 feet in diameter) Znamya reflector, was planned, and would have briefly illuminated regions of northern Europe and North America with a light up to ten times that of the full moon. However, two separate attempts to deploy the Znamya reflector failed, and both it and the Progress spacecraft which carried it later entered the atmosphere and burned up.
The Russian-based Space Regatta Consortium, which designed and built the Znamya reflectors, has announced potential plans to deploy an entire "constellation" of such reflectors, each up to 200 meters (650 feet) in diameter and providing illumination to Earthbound targets up to 100 times that of the full moon. Ostensibly these would be used to provide light to regions in high polar latitudes and to assist in, for example, search-and-rescue operations, and could also serve as prototypes of space reflectors which could provide propulsion to interplanetary spacecraft. However, the prospect of such a scenario has not been greeted with overwhelming joy by the world's astronomers, and several astronomical organizations around the world have expressed strong concerns about this proposal. And although such reflectors would presumably be tightly controlled, as was demonstrated with the recent Znamya experiment Murphy's Law has a way of entering things, and if control were to be lost over one or more of these reflectors it could wreak significant havoc with astronomical observations and other activities around the world.
The idea of using solar reflectors for propelling interplanetary spacecraft has received a fair amount of attention during recent decades and may very well be a viable way of traversing the solar system. There may indeed be merit in using spaceborne illumination for certain restricted types of activities here on Earth. As we progress into the future let us indeed find ways to utilize sunlight to our benefit, but at the same time, let us make sure that we preserve the beauty and the inspiration of the nighttime sky for ourselves and for those who follow us.
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