This makes it difficult to see the stars well, and even the moon can be dwarfed. The effect is compounded by particles, aerosols, and gases that reflect electromagnetic waves. Hong Kong is the most lightly polluted city on the planet , according to a study by the University of Tokyo: the night there is a thousand times brighter than the limit set by the scientific community.
Among the detailed investigations on this issue, the most important was the one that led to the first world atlas of zenith brightness in 2001, the only one that exists to date to measure this factor globally. The study, carried out by Italian and American scientists using satellite data and images, revealed that half of Europeans and two-thirds of Americans cannot see the Milky Way with the naked eye. Andalusia, Levante, Madrid, Catalonia, Cantabrian-Ebro Valley and the Atlantic axis (La Coruña-Lisbon) are contaminated areas in the Iberian Peninsula.
As for cities, Madrid, Barcelona and Seville are the most illuminated points. As the problem seems to grow, the International Association for the Dark Sky (IDA, for its acronym in English) has proposed to conserve the night sky as much as possible and collaborates with the Skyglow project.
Its promoters are the photographers Gavin Heffernan and Harun Mehmedinovic, who show in their images what the celestial vault would be like if American cities did not suffer from excessive lighting. One of the first locations chosen was the city of Los Angeles: according to the IDA, the brightness of its lights is visible from an airplane located more than 200 miles high.
