Light Pollution

Preserving Dark Skies:

Efforts to measure light pollution and work with the local and world community to preserve the heritage of the naturally dark night sky.

IAU Commission 50 Working Group on Controlling Light Pollution

Several years ago, the International Astronomical Union's Commission 50 on "Protecting Existing and Potential Observatory Sites" formed a Working Group on "Controlling Light Pollution".  Information about this working group and the data and references collected by them can be found at .  Their most important product so far is Cinzano et al.'s 'First World Atlas of the Artificial Night-Sky Brightness'.  Some form of second edition will provide a baseline of ~10 years if suitable funding can be identified soon to extract the data from the DMSP archives.  A Second World Atlas will provide a much more reliable and pragmatic baseline for extrapolations of potential site deterioration than the population modelling we currently rely on (and which is only partly valid near large, open-pit, mining developments, for example). The IAU has given high priority to protecting sites in Northern Chile (such as Cerro Paranal) and other key parts of the world (such as Mauna Kea, Hawai'i ) where heavy capital investment in astronomy is taking place.

Sky Brightness over Cerro Pachon and Cerro Tololo

Light pollution from nearby cities (La Serena, Coquimbo, Ovalle, Andacollo, and Vicuña) has been a concern over the last decade, due to the rapid growth in population and development which this region of Chile has undergone. AURA and CTIO have undertaken an agressive campaign - which began in December 1993 - both locally in the surrounding cities and at the Chilean congressional level, to alert the Chilean public and governing agencies, in time, to these concerns (e.g., CTIO's web page in Spanish on light pollution at and the web page in Spanish of the Oficina Para la Proteccion de los Cielos del Norte de Chile, at 

However, it is not the current level of lighting which is worrisome. The concern over the last decade has been what changes the future development of the region will bring to what are presently very dark skies (which we of course want to keep that way). A CTIO study by Alistair Walker and Hugo Schwarz, "Night Sky Brightness at Cerro Pachon", presents recent numbers and several current projections, depending on population growth and the success of lighting controls. The study demonstrates that with successful lighting awareness campaigns, such as that which CTIO/AURA has launched, Cerro Pachon and Cerro Tololo can continue to be prime astronomical sites far into the future.  The Intendente of Chile's 4th Region (the maximum government authority for the area in which Pachon and Tololo are located), at the international, dedication ceremony for SOAR in April 2004, devoted his speech to communicating his recognition of the importance of maintaining the dark skies over Pachon and Tololo (see page 3 of the above link).

By May 2004, when we last took a census, 1/3 of all the municipal street-lighting fixtures in the three astronomically-sensitive regions of Northern Chile had been changed to direct  light  downwards.  Evidence is clear in the towns and cities that the program is continuing to gain momentum. Furthermore, post-curfew reductions in sky bightness have now been detected low on the horizon from Cerro Tololo.   This remarkable, national-level enterprise  (involving a direct, capital investment of ~US$10M by generally cash-strapped Chilean municipalities) is expected to be completed (including La Serena and Coquimbo) by October, 2005, as required by Chile's Presidential Decree No. 686, the "Norma Luminica".   Using conservative population-growth models (only, so far), a reduction of a factor of two in artificial night-sky brightness will extend the current lifetime of any observatory by about two decades, as it will take this long before the pre-changeover brightness level is again reached. A pragmatic, more pessimistic estimate of 7%/annum growth in artificial light pollution after the municipal lighting changeovers would provide 10 years of breathing space if a factor of 2 reduction is achieved as a result of the changeover, and 16 years if current levels are reduced by a factor of 3.  We expect that at least the factor-of-two reduction will have occured during the period 2004-2005 and we will continue to monitor it closely.

Environmental legislation in Chile is reviewed and updated every 5 years, by law.  We will use the breathing space to work with the authorities over the next two cycles (5yrs/cycle for Chilean environmental legislation) to control light pollution by tightening the current legislation (following the successful leadership given by Flagstaff and Tucson) to include lighting zones with lumen (or wattage) caps and so on - and so move on beyond the simple first step "Ilumine el Suelo, no el Cielo" (light the ground, not the sky).  This next step in the legislation can, for example, emphasize more specifically and quantitatively the economic advantages of measuring the light and comparing against international lighting-engineering norms - i.e. using the additional light that used to go up into the sky to light the intended target and select the appropriate power needed for each luminaire (light fixture).  The appearance of double-ballast lamps in Chile means that one can, for example, reduce the power to the city's streetlights by 40% after lighting curfew.  Payback time on capital investment is then much faster.  Achieving these savings will, however, of course not permit adding more lights while maintaining the same excessive wattage in all the existing ones!  We are working closely with the International Dark Sky Association (the current AURA-O Director is a member of the IDA Board of Directors) in extending their new "Model Lighting Ordinance" (now available in draft form from the IDA) to the realities beyond the borders of the United States. 

We are also working closely with the environmental and education authorities in Chile as part of a co-ordinated effort to educate the children in this region as to the options thay have for controlling their environment in the future.  Finally, we are emphasizing the further economic advantages of  dark skies for "astro-tourism" for the region. Of the 46,000 visitors to the Mamalluca Municipal Observatory in 2003 - versus a total of 9,000 in 1999 - 14,000 came from outside Chile in 2003. This number of foreign visitors is similar to the entire population of the town; all these visitors had to sleep and eat somewhere (at a time when local tourism was still suffering from the collapse of the Argentinian economy). Chile's President Lagos - a keen amateur astronomer - opened the Collowara public observatory in Andacollo in late June, 2004; he and the Minister of Finance gave strong support for these concepts in their speeches.  We have begun to work closely with Euro-Chile and the local municipalities in this context to develop and co-ordinate a "Ruta Astronomica" in the Elqui and Lamari valleys (nearest Tololo and Pachon; p3 of the above link to the March 2003 NOAO Newsletter refers to support by Intendente Felipe del Rio Goudie for protecting the skies over Chile's IVth Region).

The priorities and timing of these efforts have concentrated in the areas most likely to threaten Pachon and Tololo in the decades to come - beginning with nearby Vicun~a in 1993 and increasing the relative emphasis on La Serena and Coquimbo once maps from the First World Atlas of the Artificial Night Sky Brightness became available.  Estimates for the evolution of the differential contributions of the neighboring towns over the last decade and into the future can be seen in the approximate models presented by Alistair Walker and Hugo Schwarz.  These models provide further guidance to our selection of priorities for future efforts and confirmation of our choices over the last decade; they will be refined when we have access to a Second World Atlas of the Artificial Night Sky Brightness.  We will need to remain vigilant.

NOAO Newsletter Articles

Other sites of "Dark Sky" Interest

International Dark Sky Association  See also useful links from this, the most visited, central, international site.

Office for the Protection of the Skies of Northern Chile (OPCC)  This Office, under the direction of Sr. Pedro Sanhueza, is a jointly funded effort by the Chilean National Environment Commission, AURA, ESO and OCIW.

LiteLynx Cliff Haas' page of links from around the world

Google Light Pollution Directory  Light Pollution links with summary descriptions and comment (listed in Google PageRank order).

Last modified: 10 May, 2006
  Malcolm Smith: