cosine recently installed a sky brightness sensor next to our weather station in Warmond. Understanding the world around us makes it possible to improve our environment. cosine develops measurement solutions for our customers, but we also want to contribute to public knowledge.
Why install a sky brightness sensor? Light pollution seems to be ever increasing, so we decided to start measuring the sky darkness from our office in Warmond and report our observations to crowd science platforms, contributing to better insights for our decision makers.
We recently installed a Unihedron Sky Quality Meter (SQM-LE) on our roof. The system consists of a silicon photo-diode and a current-to-frequency converter chip. The brighter the sky, the higher the measured frequency, and vice-versa. The system provides its readings in magnitudes per square arcsecond, which is a logarithmic measurement where large changes in the sky brightness correspond to relatively small numerical changes. Magnitudes are an astronomical unit of measure for object brightness, where the full Moon is about -12.6 mag, Vega about 0 mag and a really dark sky corresponds to about 22 mag. To see the milky way you need 20.2 mag/arcsec^2.
Platforms we now report to daily include Was Het Donker, a Dutch initiative of a number of institutes, such as the University of Groningen. We also report to Light Pollution Map and to the Sky Brightness Monitoring Network. And you can always find the readings of our Sky Quality Meter on our own website.
Our first measurements show that the sky above cosine is slightly darker than the sky above the nearby city of Leiden and much brighter than the Northern part of the Netherlands. This Sky Quality Meter enables us to not only compare, but also quantify sky brightness. It looks like it will be a huge challenge for many large cities in Europe to reduce their light pollution.
We invite anyone who has a suggestion for something we could measure to contribute to crowd science or your particular business to get in touch with us.