How dark is the sky in Hesse?
Sky darkness for 16 towns and parks in Hesse, worked out from NASA satellite images of light at night (2025). 5 of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Hessian Rhön Nature Park (21.53, Bortle 4), the brightest Frankfurt am Main (18.61, Bortle 7). The bright core of the Milky Way never climbs clear of the horizon haze anywhere in Hesse while the sky is fully dark; the rest of the band passes overhead, with the longest moonless nights from September to March.
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 Hesse
- Hessian Rhön Nature ParkBortle 421.53
- Kellerwald-Edersee National ParkBortle 421.51
- High Vogelsberg Nature ParkBortle 421.47
- Lahn-Dill-Bergland Nature ParkBortle 421.36
- Habichtswald Nature ParkBortle 421.34
Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.