For most U.S. residents and many Europeans, the only late night Milky Way sightings will involve trips to the corner grocery to alleviate chocolate cravings.

More than two thirds of the U.S. population, about half the people in Europe and a fifth of the world's population can no longer see the grand cloudy strip of stars representing the center of our galaxy, popularly called the Milky Way, according to a new study that examined how light bounces around in Earth's atmosphere.

Light from homes, factories, parking lots and highway billboards -- light pollution, as astronomers call it -- creates nights that are no darker than twilight for much of the world's population, the study concluded.

Backyard astronomers have bemoaned light pollution for years. What used to appear as a vast sea of thousands of stars -- a milky swath overhead that actually represents millions of points of light -- is now only visible in the most remote locations. Large-scale studies have looked into the phenomenon by focusing on satellite observations, where only the light leaving Earth's atmosphere can be recorded.

The new study, "First World Atlas of Artificial Night Sky Brightness," is among the first to relate the effects of light pollution to the number of people who live in affected areas. It modeled how light scatters through the atmosphere, bouncing off water vapor and other molecules. Some of this light is bounced back to the ground after being shot every which way, impairing the view of stars even for people who are not near the light source.

Resulting maps of the world show that many areas which appear dark in visible-light satellite images, such as lakes and other uninhabited or sparsely population locations, are in reality affected by light pollution coming from nearby bright places.

The research was done by Pierantonio Cinzano and Fabio Falchi of the University of Padua, Italy, along with Chris Elvidge of NOAA's National Geophysical Data Center in Colorado.

Elvidge produced the base maps of "top-of-the-atmosphere brightness" from satellite data. The Italian group did the atmospheric modeling that then computed how much light would have never made it that high. The team then correlated the data to population density information.

"There are very few measurements made of what's called artificial sky brightness," Elvidge told SPACE.com. "We've tried to pull some of those together that we considered valid and compare that against what the model predicted." The team is working on a separate research paper to discuss the results of this comparison.

Elvidge said the study is the first of its kind to cover the whole Earth. However, some locations, including Alaska and other regions near the poles, were left out because highly reflective snow cover was not figured into the model.

The study was based on data collected in 1996 and 1997.

"It is undoubtedly worse today," Cinzano said in a press release.

The light that fills the night sky comes from many sources. Astronomers say much of it, what they call wasted light, could be prevented. Billboards are one example -- their light is often reflected needlessly upward. Poorly directed security lights are also cited. Studies have shown that money could be saved by properly directing a more appropriate amount of light in some cases.

At a 1999 symposium on the topic in Vienna, astronomers claimed wasted light has annual costs of $2.9 million in London and $13.6 million in New York City.

Not all the news is bad.

A half-dozen states have passed laws to help reduce light pollution, according to the International Dark Sky Association, which lobbies for more subdued illumination. And several state and national parks around the country have recognized the value of dark skies and undertaken programs to try and preserve them.

Even some municipalities are developing solutions.

Los Angeles is notorious for its sea of light that washes out the stars for miles around, including atop Mount Wilson, a nearby observatory more than 5,000 feet up in the mountains. But the region has worked to replace mercury vapor street lights, which astronomers say are terrible emitters of excess light, and replace them with low-pressure sodium lights. These dimmer and yellowish lights interfere less with starlight, astronomers say.

"And so, ironically, the night sky is actually darker over L.A. than it was 15 years ago," said Harold A. McAlister, a Georgia State University professor who frequently studies stars from Mount Wilson.