  Light pollution is recognized as a global issue that, like other forms of
anthropogenic pollution, has significant impact on ecosystems and adverse
effects on living organisms. Multiple evidence suggests that it has been
increasing at an unprecedented rate at all spatial scales. Chile, which thanks
to its unique environmental conditions has become one of the most prominent
astronomical hubs of the world, seems to be no exception. In this paper we
present the results of the first observing campaign aimed at quantifying the
effects of artificial lights at night (ALAN) on the brightness and colors of
Chilean sky. Through the analysis of photometrically calibrated all-sky images
captured at four representative sites with an increasing degree of
anthropization, and the comparison with state-of-the-art numerical models, we
show that significant levels of light pollution have already altered the
appearance of the natural sky even in remote areas. Our observations reveal
that the light pollution level recorded in a small town of the Coquimbo Region
is comparable with that of Flagstaff, a ten times larger Dark Sky city, and
that a mid-size urban area door to the Atacama Desert displays photometric
indicators of night sky quality that are typical of the most densely populated
regions of Europe. Our results suggest that there is still much to be done in
Chile to keep the light pollution phenomenon under control and thus preserve
the darkness of its night sky - a natural and cultural heritage that is our
responsibility to protect.
