Mankind will lose its view of the stars altogether -- unless we learn very soon to shine our light onto the ground, where we need, instead of into the night sky. Astronomers at the International Astronomical Union (IAU) General Assembly in Manchester (UK) have sounded a wake-up call for everyone on the planet.

A composite of over 200 images made by satellites orbiting the Earth showing the United States at night. The scans were made by the U.S. Air Force's Defense Meteorological Satellite Program Operational Linescan System. Man-made lights also emit in the near UV, and cities can be a large source of "light pollution" in this range just as in the visible. The image of the United States at night in visible light demonstrates this problem. Photo: USAF

In 1999, the IAU held a Symposium on 'Preserving the Astronomical Sky', which was organized jointly with the Committee on Space Research (COSPAR) and the United Nations Office of Outer Space Affairs in parallel with the UN conference UNISPACE III in Vienna. The ongoing urgency for action was re-inforced in Manchester last week.

'Light pollution' affects everyone, not just professional observatories. An average person in the countryside away from city lights can see several thousand stars in the sky. Bit by bit, Europe is losing this view of the heavens as we add more and lamps, and waste energy by sending the light uselessly into the sky. Thousands of millions of pounds worth of energy are tossed upwards into the European sky each year -- instead of down onto the ground which we want to illuminate.

Dr Malcolm Smith, Director of the Cerro Tololo Interamerican Observatory in Chile, issued this challenge. "Look around your city or town. See how many street lamps allow plenty of light to shine upwards. Count how many stars you can see. If you are old enough to remember how the sky looked 30 years ago, could you see the Milky Way then? Can you now?"

"Bit by bit, without realizing, we are all losing a direct connection with the universe" commented Dr Smith. "Not only that, light pollution is one of the most rapidly increasing alterations to the natural environment created by humans. Reported adverse effects of this fog of artificial light involve plants and animals as well as humankind. Human culture, from philosophy to religion, from art to literature and science, has always developed in relationship with the night sky and the universe beyond. Are we going to deprive future generations unnecessarily?"

Astronomer Pierantonio Cinzano from Padua, Italy and his colleagues have been using measurements from satellites looking down at the Earth and measure the light shining upwards from the world's towns and cities. Some of his maps showing the serious extent of light pollution can be found at http://debora.pd.astro.it/cinzano/defaulten.html. Large areas in and near cities are already very seriously affected. Good lighting design can save a third or more of the cost of public lighting. Better lighting means less energy is needed and pollution from unnecessary power stations can be reduced.

Preserving dark, starlit skies
There are still pristine, remote, dark-sky sites where astronomers construct huge telescopes to reach out to the edges of the universe. The most famous of these special sites are in Hawaii, Chile and the Canary Islands. Even in these places, city lights can be seen. A great effort is being made to protect these sites and to avoid the situation that has already affected most of Europe by obtaining legislation to control the wastage of light from cities and towns near these special regions. Dr Smith spoke about the success in a town in Chile near the Cerro Tololo Observatory which is saving 40% of its former annual electricity bill, uses its starlit sky to attract amazed tourists from urban areas in Europe and the USA, and uses its Municipal Observatory to educate local school children in the need to preserve this natural treasure of mankind.

Radio interference problems too
Also at the meeting, radio astronomers discussed issues relating to the interference they encounter when using large radio telescopes. Mobile telephones, television, satellites and airport radars are all essential to modern life but they create a noisy radio environment that makes it very difficult to make sensitive astronomical measurements of quasars, pulsars, black holes and the cosmic microwave background. As an example, the tiny amount of energy transmitted by a mobile phone could easily be picked up by the giant 250-foot radio dish at Jodrell Bank -- even if the phone were on Mars!

Radio astronomers are working with the regulatory authorities to reserve slices of the radio spectrum for receiving natural signals from the universe amid the cacophony of modern life. They are also seeking to establish 'international radio quiet zones', preserves with special regulations rather like national parks. Such a zone might well be the site of a huge square-kilometre array of radio telescopes now being proposed by the world's radio astronomers.