Flüelapass at Night

Graubünden, Switzerland 2400 m

Date:	23.12.2025	Time:	23:45 CET
Exposure:	9 x 13 s, 10 x 30 s	Field of View:	360° x 180°
Camera:	Lumix S5IIX	Optics:	18 mm f/2.0 and f/2.8
Place:	Flüelapass, Switzerland	Photo:	Till Credner

The brightness in the zenith was 21.27 mag/arcsec² at the time of the above photography, 23:45 CET, 23.12.2025. The darkest measured value was 21.30 mag/arcsec² at 0:43 CET, however, in a narrow time span between about 11 pm and 1 am. 21.30 mag/arcsec² is still a factor of 1.9 brighter than a natural dark night sky due to the light pollution of Davos (for example). The winter milky way added further brightness and thin clouds scatter light pollution from the ground. The bright red light of Flüela-Hospiz shines into the surrounding alps. The SQM-device for measuring the sky brightness should not be sensitive at these long wavelengths. Measurements were obtained each minute with a SQM-LU-DL, serial number 2030. Temperatures were between -7 and -9°C.