Astronomy is facing a present and future severe problem with adverse environmental impact, just as is the rest of mankind. While we all suffer from air and water pollution, amateur and professional astronomers are finding the universe disappearing from view, due to light pollution, radio interference, and space junk. We must build awareness of these issues and seek solutions.

Light Pollution is a severe problem for amateur and professional astronomers, and, indeed, for the general public. All these suffer from a lack of awareness of the issues, however. Poor quality outdoor nighttime lighting has several major problems: light trespass, glare, clutter and confusion, urban sky glow, and energy waste. There are solutions to the light pollution problem, most involving the use of better quality lighting. We all must educate our colleagues and the public about the issues, and push for solutions. Quality lighting is compatible with dark skies, and with energy savings. Our view of the universe, as professionals and as the public, and our children’s, depends on our being successful.

An image of the entire earth at nighttime is assembled for the first time. It consists of a mosaic of photographs, all taken at local midnight in the 400-1100 nm band, made by the Defense Meteorological Satellite Program over the period 1974-84. Photographs were selected for freedom from clouds, lack of moonlight, high sensitivity, and suitability to illustrate various temporal phenomena. The image primarily reveals activities of humankind such as urban street lighting, rangeland burning, slash-and-burn agriculture, natural gas burnoffs in oilfields, and squidding. Although light pollution in urban areas creates a striking map, at the same time it devastates astronomical observation and removes much of humankind from any familiarity with the night sky.

Photographic documentation of outdoor lighting installations has been underway in Tucson and throughout Arizona for some time. Such photos show what can be done to minimize the problem of light pollution, illustrating examples of both good and bad lighting designs and installations. Copies of such photos (mostly in the form of slides) are available from the International Dark-Sky Association.

We report on the results of a program to measure the brightness of the night sky at the Kitt Peak National Observatory during the recent minimum in the solar cycle, a time noted for the darkest nighttime skies. We have measured sky brightness using a 0.9-meter telescope with a photoelectric photometer on seven nights in 1986 and the first half of 1987. During this period, the average sky brightness in the V (yellow) band is 21.92 magnitudes per square arc-sec. This corresponds to an increase of only 6.5 percent over the natural sky illumination, as compared to an increase of over 10 percent predicted by R. Garstang from the presence of cities and towns in southern Arizona. The continued dark skies over Kitt Peak, despite the rapid growth of Tucson’s population, can only be attributed to the effectiveness of light pollution control programs in place since 1972.

Palomar Mountain was selected as the site of the 200-inch Hale Telescope in 1934. Since then, and especially over the past decade, the population growth of southern California has had a growing adverse impact on the observatory’s environment. In 1981, a very active program was initiated to work with the local governmental agencies to prevent further deterioration of the conditions as the area continues to become increasingly urbanized. The character and scope of the program are described in the paper, as well as more general observations relating to the site preservations process.

Human life is geared to the rhythm of day and night. The day is committed to work and activity, and the night to rest, to leisure, but also to contemplation on the universe. Stars are the link between the earth-bound human existence and the eternal and infinite cosmos. So, humanity needs the night, requires the darkness – even if darkness is frightening and is considered as the personification of danger and evil.

Although China is a backward developing country, the population of many big cities has increased more than 100 percent since 1950. The light and smoke pollution for Shanghai Observatory and Purple Mountain Observatory is very serious, and in Kunming, for Yunnan Observatory, is also quite a problem. Now the only one where the observational condition is still quite good is the optical station of the Beijing Observatory, in XingLong County, Hebei Province. For the future, we plan to do some testing work on the Tibet plateau, where the population if very low, so there is no light pollution at all.

Mercury light pollution has appeared in our spectroscopic observations of the Comet 1980u made at the Observatoire de Haute Provence and spectroscopic observations of the Nova Andromeda 1986 made at the Purple Mountain Observatory. On spectra of an exposure of about one hour of the comet obtained at the 1.93m telescope of the OHP using the image tube spectrograph D (dispersion of 92 A/mm), the lines 4358, 4047 of Hgl are very strong. In the case of the nova, these lines are quite noticeable on spectra of exposure of 3 hours obtained at the 0.6m telescope of the PMO with the Marly-Nanjing spectrograph (dispersion 40 A/mm).

Observations of the night-sky brightness were organized at 106 places in Japan by a promotion of the Environmental Agency with the help of many local governments. Two kinds of measurements were carried out: 1) Number of stars were counted in a region of triangle formed by Alpha Lyr, Epsilon Lyr, and Zeta Lyr by at least 10 contributors at each point. 2) Photographs of a star field at the zenith at each point were taken with the same type of camera and film. These results gave us a good idea on distribution of night-sky brightness in Japan.

There are three astronomical observatories in Mexico working on research programs. The oldest one is located at Tonantzintla, Puebla; the largest is at San Pedro Martir, Baja California; and the youngest, not yet in full operation, at Cananea, Sonora. The one at Tonantzintla suffers, by far, the largest light pollution problems; that at San Pedro Martir has the darkest skies but is relatively close to regions of potential touristic and mining developments. In this paper we summarize the existing and potential polluting problems arising from manmade light sources near those observatories, and suggest some possible steps to be taken in order to minimize their adverse effects on astronomical observations.

In developing countries in Latin America, Asia, and Africa, light pollution takes a particular aspect due to the social and economical situation. The official reluctance to solve unpopular problems combined with a generalized ignorance create a hostile climate for any campaign in favor of astronomical observatories or amateur associations. The tropical climate makes most energy savings measures unnecessary. Obsolete industrial installations make the application of particle output control difficult or impossible. The most important contribution to air pollution, however, comes from forest fires, some of them as a cheap clearing method, others as an expressions of political discontent. To this must be added that most countries do not have yet a legislature which would permit the imposition of pollution control.

Outdoor lighting incapacitates and destroys some moths. It disturbs flight, navigation, vision, migration, dispersal, oviposition, mating, feeding, and crypsis. It may also snift circadian rhythms. Lamps may incinerate or desiccate moths, or lead to moth’s destruction by birds, bats, spider, and vehicular traffic. Conservation efforts need to consider disruptive ecological effects of outdoor lighting. Low pressure sodium lamps may reduce these effects.

During the period from 1965-1977, I was engaged in a program of selecting and acquiring a new dark sky site in California for the Lick Observatory. Even though the effort was, in the end, unsuccessful, this work did lead to several important advances in our understanding of the general problem of optimizing optical-region astronomical observing conditions. These included:

1. 1) The development of the polar star trail method of seeing measurement (Harlan and Walker 1965; Walker 1971).

2. 2) Definition of the conditions required to optimize the seeing through the use of the polar star trail method of measurement at a number of potential and established observing sites around the world (Walker 1970, 1971, 1983, 1984; McInnes and Walker 1974).

3. 3) Demonstration of the widespread effects of atmospheric pollution in reducing photometric quality at potential sites in California (Walker 1970).

4. 4) The first extensive study of the effects of light pollution on astronomical observations.

The growth of urban development and its accompanying outdoor lighting has made the search for new observatory sites increasingly difficult. A method of predicting the brightness of the night sky produced by a city of known population and distance is useful in making studies of prospective new observatory sites, as well as in studying the likely future deterioration of existing sites. Other sources of light pollution can be investigated using the same model. In most cases, several cities are responsible for the light pollution at a given site, and the predicted night sky brightness is the sum of the contributions of all the cities. In this paper, we shall review the surprisingly little work which has been done on predicting night sky brightnesses from model calculations.

There are practical ways to improve the way lighting systems are designed and operated where the objective is to control stray light from the astronomical (or other) point of view. Most efforts, however, have been direct toward the lighting hardware or operation on a micro level.

Atmospheric scattering of outdoor nighttime electric illumination produces the principal component of background sky luminance that seriously affects ground-based optical astronomy. The sources for this scattering are Tight emitted skyward directly from luminaires, and light reflected off the ground and other illuminated objects. Careful illumination engineering can thus significantly reduce background sky luminance in two ways: 1) by providing outdoor electric lighting equipment that controls the directions in which light is emitted, and; 2) by proper design of outdoor lighting systems which make efficient use of the east amount of light. Recent developments in applied mathematics and computer software have produced computational tools that are being used to design lighting equipment and lighting systems. The software system for luminaire design significantly reduces the cost of this process by eliminating the need for extensive prototyping and provides for inexpensive experimentation with new designs. The system for outdoor lighting calculations permits the design of highly controlled lighting systems that eliminate glare and upward directed light while providing light appropriate for the visual task. These two software systems are described, along with examples of their use in areas that directly affect astronomical observations.

The principal reason that public lighting exists is that it fulfills the needs for: traffic safety, personal security, comfort and pleasantness, and environmental esthetics.

Publicity is the first and most important tool in efforts to achieve control and reduction of light pollution. It should identify the ways in which light pollution is detrimental to vital human concerns, such as esthetic enjoyment of the heavens, scientific research, and the operation of cost efficient lighting, and take into account the relative importance of the various concerns for each prospective audience or readership.