Summer Milky Way, Jupiter & Saturn

According to the World Atlas of Artificial Night Sky Brigthness (2016), an estimated 80% of the world’s population lives under skyglow. In Europe and the United States, 99% of the people experience skyglow at night. Light pollution is defined as “the excessive or inappropriate use of outdoor artificial light” (National Geographic, “Light Pollution” July 2019). Scientific evidence shows that light pollution is harmful to “amphibians, birds, mammals, insects and plants” (International Dark Sky Association).

Where Are the Stars? See How Light Pollution Affects Night Skies by National Geographic
Les effets indésirables de l’éclairage | ARTE Xenius 26.09.2021

Light pollution in Switzerland

Over the past 20 years, artificial light pollution has steadily increased in Switzerland. Although the mountain areas are better for observing the night sky, according to DarkSky Switzerland, today, there is not a single place left in Switzeralnd with natural darkness. This has potentially severe adverse effects on natural ecosystems and is also affecting human health.

Light Beamer pointing directly to the night sky during Murten Licht Festival in January 2020

Geography, the size of the country and a growing population certainly play a role. Switzerland has 3 major regions: 1) the Alps (60% of total surface area); 2) the Swiss Plateau (30%); 3) the Jura mountains (10%). The majority of people lives on the Swiss Plateau.

The good news is, we can do something against skyglow. A good start is to check your home lighting. International Dark Sky Association explains it very well. For further reading go to my collection of Dark Sky links below.

Books on light pollution: the most comprehensive book on light pollution I read so far is by Annette Krop-Benesch, “Licht Aus!? Lichtverschmutzung – Die unterschätzte Gefahr” (2019). It is available in German. Annette is a Biologist – and she also has a website.

Light pollution and astrophotography

For stargazing and astrophotography, light pollution is obviously a problem. Firstly, when directly blinded by street lights and car headlights, it is impossible to observe the stars. Therefore, always make sure you observe from a location without street lights and frequent car traffic.

Secondly, any skyglow will greatly influence your pictures (below you’ll find an example with excessive skyglow from mostly street lights in my village). Even though I live dozens of kilometers away from bigger cities, my night sky is brightened by skyglow from these cities – and the public lights in my village (see image below).

For the astrophotographer, one solution is to use a filter – or go to a dark site. However, I still take a lot of pictures without using filters even though getting rid of the ugly orange/brown colour of skyglow takes considerable time.

To show the difference, check my Review of the HUTEC IDAS LPS-D1 Light Pollution Suppression Filter for Astrophotography.

Light pollution visible in an image
The Constellation of Orion & Taurus pictured through a heavily light polluted night sky in a rural area. Camera: Nikon D800, Lens: Sigma 14mm f/1.8. Settings: ISO 800, f/1.4, 20s – Switzerland, 24.11.2020 – Picture by Isabel Streit

Measuring night sky luminance

You can measure the luminance of night sky with a Sky quality meter (SQM). There are other techniques such as the Bortle Scale Interpretation of using Photographic evidence (picture above is such an example). For more details, visit the website of International Dark-Sky Association IDA.

One great resource is the Radiance Light Trend, a project led by Christopher Kyba at Potsdam University. The web app allows examining changes in nighttime light emissions from 1992 till 2020. Emissions data come from the Operational Linescan System of the Defense Meteorological Satellite Program (DMSP) satellites (data 1992-2013) and from 2012 to present from the Day/Night Band of the Visible Infrared Imaging Radiometer Suite instrument (VIIRS DNB).

Further reading

Further information on light pollution and on what you can do to help reducing it:
International Dark Sky Association
DarkSky Switzerland (CH)
Projet Perséides (CH)
la nuit est belle (CH)

Your local light pollution map:
Radiance Light Trend
Night-lights imagery by NOAA’s Earth Observation Group

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