Most of them cannot see the Milky Way and for many, the sky never gets darker than it would during natural twilight because so much artificial light brightens the atmosphere.

These are just some of the statistics revealed in the First World Atlas of Artificial Night Sky Brightness by Dr. Pierantonio Cinzano and Fabio Falchi (both of the University of Padua, Italy) and Dr. Chris Elvidge (NOAA National Geophysical Data Center, Boulder, Colorado), which has recently been accepted for future publication in the Monthly Notices of the Royal Astronomical Society.

Although there has been general awareness of the growing problem of light pollution for a number of years, this is the first time that the artificial illumination of the night sky around the world has been properly quantified and related to where people live.

The work of Dr. Cinzano and his colleagues goes far beyond simple night-time images of the Earth. They started with data acquired in 1996-97 by the US Air Force Defense Meteorological Satellite Program (DMSP), then calculated how artificial light is propagated through the atmosphere to arrive at a set of maps showing the extent and severity of light pollution around the world.

The results show that many areas that appear dark in night-time satellite images are in reality affected by light pollution caused by brightly lit neighboring places.

Dr. Cinzano commented, "Large numbers of people in many countries have had their vision of the night sky severely degraded. And our atlas refers to the situation in 1996-97. It is undoubtedly worse today."

The stark conclusions of his team include:

* More than 99% of the US and European Union (EU) populations and two thirds of the world's population suffer some degree of light pollution.

* In areas where 97% of the US population, 96% of the EU population and half the world's population live, the sky is always at least as bright as it is when there is a half Moon at one of the world's best observatory sites (where the air is dry and clear).

* For many, the sky is as bright as it is on days close to a full moon at a good astronomical site. "Night" never really comes to such places and the sky is always as bright as nautical twilight (the period of time when the Sun is between 6 and 12 degrees below the horizon).

* More than two thirds of the US population, about half the EU population and one fifth of the world's population live where they no longer have the possibility of seeing the Milky Way with the naked eye.

* For 40% of the US population, one sixth of the EU population and one tenth of the world's population, it is never dark enough at night for human eyes to become adapted to night vision.

Cinzano, Falchi and Elvidge draw attention to the fact that the adverse effects of light pollution have not been fully addressed because of the absence of comprehensive quantitative data until now.

However, the rapid increase in light pollution is one of the most dramatic changes occurring in our natural environment. It has consequences not only for astronomy, but for the whole of the biosphere, and could have unintended impacts on the future of society.

(Editor's Note: The information shown in "The First World Atlas" is calculated everywhere for sea level. This makes it possible for light pollution in different areas to be compared without the confusion of altitude effects. For more details see the full paper.)

Related websites:

Color maps are available as zipped TIFF files from . Click on "The World Atlas of sea level artificial night sky brightness" in the menu bar on the left.

Further information about other work on light pollution by Dr. Cinzano and his co-workers may be found at this website.

A preprint of the paper referred to here may be downloaded as a pdf file from this URL.

Istituto di Scienza e Tecnologia dell'Inquinamento Luminoso (Light Pollution Science and Technology Institute), Thiene, Italy

(Reference: Accepted for publication in the Monthly Notices of the Royal Astronomical Association - publication date to be scheduled.)

[Contact: Dr. Fabio Falchi, Dr. Pierantonio Cinzano, Dr. Chris Elvidge]

14-Aug-2001