New dark sky sensor monitors brightness of starry skies above Delft campus

How dark are the starry skies above the campus in Delft? To find out researcher Sebastiaan de Vet and technicians installed a sky quality sensor at the Rooftop Laboratory of the Faculty of Aerospace Engineering. It is part of the national network ‘Was het donker’ (“Was it dark?”), which measures the sky brightness across the Netherlands.

The observation network ‘Was het donker’ is an initiative of the Kapteyn Institute for astronomy and ScienceLinX of the Faculty of Science and Engineering of the University of Groningen. It was set up as part of the project ‘Darkness of the Wadden area’ that is committed to raising awareness for the importance of dark skies.

The night-time measurements provide insight into dark sky quality and as such the degree of light pollution. Reducing light pollution can help limit energy waste, contributes to nature and preserves darks skies, giving us a view on starry sky in return. In addition to the Wadden area, measurements are also made from other places in the Netherlands. Since 17 May, the sensor at the rooftop laboratory of the Faculty of Aerospace Engineering has come online to join the national network.

Below is a plot of the first night of recorded data from Delft on the night of 17/18 May 2023. Delft lies close to one of the most light polluted areas in the country, which limits the amount of stars that we can observe. You can compare the most current data from Delft with those recorded at other places, or browse the raw data archives of all stations via the website

Figure: Data recorded on the moon-less night of 17/18 May. The vertical axis shows the sky brightness: a higher value indicates a higher limiting magnitude, which signifies a darker sky (you can observe more stars). The variation of the sky brightness in the later part of the night is due to cloud layers passing overhead, increasing the reflected light and as such brightness.