快猫短视频

Half the people in the European Union and 80 per cent of those in the US
can鈥檛 see the Milky Way, astronomers warn. They hope that the first world atlas
of light pollution, to be published soon, will help their campaign to tackle the
glare from artificial lighting in towns and cities.

鈥淚t provides a nearly global picture of how mankind is proceeding to envelop
itself in a luminous fog,鈥� say the scientists who drew up the atlas. 鈥淭he night
sky appears more seriously endangered than commonly believed.鈥�

Astronomers have been painfully aware for decades that light from street
lamps and other artificial sources is blotting out our view of the heavens. This
is one reason why new observatories are built in thinly populated areas. But
according to Pierantonio Cinzano of the University of Padua, no one knew the
full extent of the problem because until now there have been no global surveys
of artificial sky brightness.

So he and his colleagues studied satellite images gathered by the US Air
Force Defense Meteorological Satellite Program during 1996 and 1997. The images
revealed light sources on Earth鈥檚 surface during cloud-free nights. They ignored
lights that appeared only once or twice over a 28-day period, in case they came
from temporary sources like wildfires.

Using mathematical models of how the atmosphere scatters light, they then
calculated how bright the sky appears at sea level on a clear night at any given
place. The resulting map of light pollution will appear in Monthly Notices
of the Royal Astronomical Society.

The map reveals that the problem affects nearly every country in the world,
not just the developed countries as is commonly believed. By comparing the map
with the distribution of population, Cinzano found that more than 80 per cent of
people in the US, and a quarter of all people worldwide, live in regions where
light pollution makes the sky brighter than it is on nights close to a full Moon
viewed from the best astronomical sites.

Cinzano hopes governments will introduce legislation to curb the problem.
鈥淟ight pollution is growing with rates even of the order of 10 per cent per
year,鈥� he warns.

But there are some cities that set a good example, Cinzano adds. Venice
scored top marks as the only city in Italy with a population of more than
250,000 from which you can see the Milky Way from the city centre on a clear
night. 鈥淭his is due mainly to the unique low-intensity romantic lighting of this
city, which deserves to be preserved,鈥� he says.