Light Pollution in Zagreb Greater than in Vienna, Hong Kong

Light pollution of the sky above Zagreb, resulting from the use of artificial light, averages 16.9 magnitudes, which is greater than the light pollution of the sky above Hong Kong, according to research results published in a recent issue of the Journal of the Mining, Geology and Petroleum Engineering Faculty in Zagreb.

Professor Željko Andreić from the RGN has measured the brightness of the sky above the faculty building near the center of Zagreb for six years, starting from January 2012, and found that the average brightness of the night sky during this period is approximately constant, except for annual variations caused by changing meteorological conditions.

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Nighttime minima, maxima, and average sky brightness significantly change due to meteorological conditions, often with amounts between 2 and 3 magnitudes, it is emphasized.

The exact term for brightness values is the standard astronomical measure “magnitude per solid angle per second squared” (mag/arcsec²).

Clear nights are less light-polluted, while cloudy nights are more light-polluted, so the sky brightness values cluster around two maxima, about 15 magnitudes on clear nights and about 18.2 magnitudes on cloudy nights, Andreić points out.

Both values are slightly lower in spring, i.e., summer, he adds, noting that brightness values less than about 16.7 magnitudes are attributed to clear nights.

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The center of Zagreb has been fully formed for a long time, and the sky pollution above it is constant, but the situation may be different in rapidly growing suburbs, explains Andreić, adding that additional measurement locations in the suburbs are needed to assess the effects of that growth on light pollution.

Comparison with Vienna and Hong Kong shows that Zagreb produces disproportionately high light pollution, explains Andreić.

In Vienna, which has a population of about 1.7 million, the average brightness of the night sky ranges between 16.3 and 19.1 magnitudes.

Thus, the cloudy night sky above Zagreb is 1.3 magnitudes brighter or approximately 3.2 times brighter than the sky above Vienna, while the clear night sky is about 0.9 magnitudes brighter, or about 2.3 times, Andreić emphasizes, adding that Hong Kong, with nearly nine times the population, pollutes the sky less than Zagreb.

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Light pollution is the alteration of natural light levels in nighttime conditions caused by artificial lighting. It causes many harmful phenomena such as health problems, disruption of ecosystems, and interference with astronomical observations. The highest light pollution is present in developed industrial countries.

Nighttime light during sleep interrupts the production of melatonin, a hormone important for human health, which leads, for example, to an increase in breast, prostate, and colon cancer, as well as sleep disorders and symptoms of depression.