Amateur astronomers are collaborating on an international project to track urban light pollution in the atmosphere, which clouds our view of the stars.
As urban light pollution grows as a problem, a global survey aims to map its spread, with the help of amateur star gazers.
According to a report in Cosmos magazine, the project is known as the Great World Wide Star Count, which pools skyward observations taken by citizens around the world.
The project, in its second year, is organised by the University Corporation for Atmospheric Research, (UCAR) a consortium of 70 universities and the U.S. National Centre for Atmospheric Research.
In 2007, more than 6,600 observers on all seven continents took part. From the data, UCAR created maps of star visibility around the world.
"Last year's results showed a strong correlation between dense development, where there is a lot of light, and a lack of star visibility," said Dennis Ward of UCAR's Office of Education and Outreach.
"Without even being aware of it, many of us have lost the ability to see many stars at night," he added.
Participants in the northern hemisphere will look for the constellation Cygnus, while those in the southern hemisphere will turn their attention on Sagittarius.
By focussing on particular constellations, scientists can more accurately compare how star visibility differs around the world.
Participants can download forms from the website. People encountering cloudy weather can record their observations of the clouds instead.
This year, the survey runs from October 20 until November 3.