Report: Zagreb sky more light polluted than in Hong Kong

RGN professor Zeljko Andreic regularly gauged the brightness of the sky above the faculty's building near Zagreb city centre for six years, and established that the average brightness of the night sky was at a constant level at all times, with the exception of seasonal differences caused by weather changes.

Nightly minimums, maximums, and medians of sky brightness change considerably due to weather conditions, often by two or three magnitudes, according to the findings.

Clear nights have less, while cloudy nights have more light pollution, with sky brightness being about 15 magnitudes on clear nights and about 18.2 on cloudy nights, Andreic said. Both readings are a little lower in the spring and the summer.

Compared with Vienna and Hong Kong, Zagreb produces disproportionately high amounts of light pollution. In Vienna, which has a population of about 1.7 million, the average brightness of the night sky is between 16.3 and 19.1 magnitudes.

A cloudy night sky in Zagreb is 1.3 magnitudes brighter, or approximately 3.2 more times, than in Vienna, while a clear night sky is 0.9 magnitudes brighter, or about 2.3 more times, Andreic said, adding that Hong Kong, which has an almost nine times larger population, causes less light pollution than Zagreb.

Light pollution can directly affect human health, as bright night lights prevent the production of melatonin in human bodies, which is thought to cause a higher incidence of breast, prostate, and colon cancers, as well as sleeping disorders and depression.

Hong Kong is notorious for its light pollution and is considered one of the most light polluted cities on the planet.

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