A brief account is given of how environmental challenges to astronomy have grown and diversified and how the IAU has addressed the problem. In the 1970s and '80s, appeals and Resolutions of increasing urgency were addressed to governments and other authorities. In the 1990s, interdisciplinary organisations such as ICSU and UNESCO were enlisted as allies. The present Symposium marks the beginning of a new phase, where direct collaboration with United Nations Member States is sought through the UN Committee on the Peaceful Uses of Outer Space.

The roles of the International Astronomical Union, the other ICSU Unions, UNESCO and the UN are reviewed in order to assess the way forward to resolve a unique situation - the impact of civilisation on the observational procedures of a particular science - astronomy. Action to create a modus vivendi to allow the continuance of vigorous astronomical science within a vibrant technological society is suggested.

There is no question of the need for outdoor lighting to improve the effectiveness of our night-time environment. However, too much of the lighting installed to try to meet this need actually compromises the purpose, and it too often adversely affects the night-time environment, including our view of the stars and of the Universe above us. This urban sky glow severe impacts on all of astronomy, amateur and professional, as well as those of the public who enjoy and profit by the beauty offered by a prime dark sky. In the present paper, I review the issues involved and suggest guidelines to minimize these negative aspects of poor night-time lighting. With good outdoor lighting we all win.

A basic-level summary is provided of work since late 1993 to control light pollution in Chile. The purpose of this article is to stimulate such work inside Chile and to promote good lighting in developing countries in general. Chile is selected as the case study because of its critical importance to optical and radio astronomy, and the related economic and cultural benefits for Chile and the world. Examples are presented in some detail in order to illustrate adjustments that have been made to accommodate local scientific, cultural and economic realities and to show that it is necessary to anticipate the issues involved in controlling light pollution several decades before it would otherwise become a problem. It is hoped that international organizations such as the IAU, the IDA and the CIE can soon promote programmes in Chile that can serve as pilot programmes for other parts of the developing world.

In 1984 the International Commission on Lighting (CIE) set up a Technical Committee TC 4.21 to study interference by artificial light in astronomical observation. The resulting document “Guidelines for minimizing sky glow” (CIE No. 126) complements previous CIE documents from 1978 and the joint CIE-IAU (International Astronomical Union) publication of 1984. In this paper, we demonstrate how high performance luminaires based on more global and pertinent criteria can significantly reduce sky glow.

This paper explains the structure and organization of the International Commission on Illumination (CIE), shows how it works, and describes its objectives and achievements. It gives details on the technical work done in the CIE Divisions and Technical Committees, and mentions some examples of the work in progress, emphasising those in connection with the subject of this conference. Quality lighting is the key to reducing light pollution. CIE is aware of the problem and takes it very seriously. CIE Divisions are working on problems such as glare, quality lighting, light trespass, light pollution and energy efficiency. In this endeavour CIE is also co-sponsoring this conference.

The paper describes the activities of CIE in the field of fighting sky glow. The most recent CIE publications are briefly discussed, as well as suggestions for further work. Modern developments in road lighting as well as alternatives to it are briefly discussed.

Division 5 of the CIE deals with the subject of “Exterior and other Lighting Applications” and has since 1991 had a Technical Committee (TC5.12) working on a “Guide on the limitation of the effects of obtrusive light from outdoor lighting installations”. This Committee did much of its work under the chairmanship of Dr. Alec Fisher of Australia, who has now retired and passed on the work to the current author. The present report outlines the content of the proposed Guide and details its relevance to help preserve the astronomical sky. It also highlights the close links with CIE Committee TC4.21, which works directly on the problems of sky glow.

The damage to the dark-sky resource upon which ground-based astronomical observatories depend is substantial and increasing, even at what are considered premier dark-sky sites. Due to its nearly monochromatic output at the Na I resonance doublet near 589 nm, extensive use of low-pressure sodium (LPS) lighting in areas near astronomical observatories offers the potential preservation and even restoration of dark skies at other wavelengths, as well as minimal impact on the lighting needs of surrounding communities. Flagstaff, Arizona, with extensive use of LPS for general area lighting, has shown that this goal can be achieved.

In the Flemish region of Belgium, yearly environmental reports (MIRA) are made on the status and evolution of the environment and its policy. Since 1996 light pollution and light impediment are among the topics considered. By using indicators which can be compared in the different reports it is possible to estimate the evolution of light pollution and light impediment. Suggested changes in lighting policies could save the Flemish region as much as 18 million EURO per year.

We present maps of the artificial sky brightness in Europe in V band with a resolution of ~1 km. The aim is to understand the state of night sky pollution in Europe, to quantify the present situation and to allow future monitoring of trends. For each terrestrial site the artificial sky brightness in a given direction on the sky is obtained by integrating the contributions from each surface area in the surroundings, using detailed models of the propagation in the atmosphere of the upward light flux emitted by the area. The top-of-atmosphere light flux is measured by the Operational Linescan System of the Defence Meteorological Satellite Program (DMSP) satellites. The modelling technique, which was introduced and developed by Garstang, takes into account the extinction along light paths, double scattering of light from atmospheric molecules and aerosols, and Earth curvature. Use of this technique allows us to assess the aerosol content of the atmosphere.

The U.S. Defense Meteorological Satellites provide an opportunity to measure the uplight produced by artificial lighting on the ground. In this study DMSP data are used to measure the integrated at-detector radiance of a number of communities in the American Southwest in an attempt to evaluate the effectiveness of outdoor lighting codes. Use of DMSP data in this manner is complicated by many factors, and some of these are briefly discussed.

Light pollution is a serious problem, not only to astronomy but also to the environment and the economy. The amount of light energy loss from Cairo has been calculated using data obtained at Kottamia Observatory in 1980 and 1995. The amount of energy loss is much greater in 1995. Comparison with a number of other world cities is given. These results show that much money is being wasted. Recommendations to overcome the problem, and the corresponding savings, are given.

The situation in terms of regulation of light pollution in Italy is here presented. The activity, started with the effort of amateur astronomers, lighting engineers and professional astronomers, is split into several actions oriented both to the local and national levels. One of the first goals was an ordinance of the city of Frosinone providing specific guidelines for lighting. The provinces of Valle d'Aosta and Veneto have followed up with local laws. The regional law of Valle d'Aosta includes a safeguard for nocturnal fauna from light pollution. The regional law of Veneto includes protection of the environment, observatories and astronomical sites. To avoid a proliferation of local laws, a national Italian bill was submitted and it is still under discussion. Bill No. 751 has been approved by the general assembly of the Italian Astronomical Society and provides more specific guidelines and standards concerning lighting in order to avoid unnecessary upward illumination and to reduce glare. At the same time a new technical standard, UNI 10819, has been settled after long debate among UNI (Italian National Standards Institute), the Italian Astronomical Society's Light Pollution Committee, lighting engineers and representatives of lighting manufacturers.

After 3-year discussions within a working group of the Japanese CIE and then 2-year discussion under a committee of the Environmental Agency in Japan, “Guideline for Light Pollution - Aiming for Good Lighting Environments” was published by the Environmental Agency. This is the first governmental guideline in the world and therefore a good example to be discussed in the other countries.