How dark is the sky in Hauts-de-France?
Sky darkness for 7 towns and parks in Hauts-de-France, worked out from NASA satellite images of light at night (2025). None of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Saint-Quentin (19.63, Bortle 5), the brightest Calais (18.86, Bortle 7). The bright core of the Milky Way never climbs clear of the horizon haze anywhere in Hauts-de-France while the sky is fully dark; the rest of the band passes overhead, with the longest moonless nights from September to April.
Numbers like 21.95 or 16.97 are the brightness of the sky overhead on a clear, moonless night, in mag/arcsec². The scale runs backwards: a lower number means a brighter sky, from about 22 for a natural sky to about 17 in a city center.
How the readings are made
Darkest skies in Hauts-de-France
Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.