YozoraAtlas

How dark is the sky in Grand Est?

Sky darkness for 10 towns and parks in Grand Est, worked out from NASA satellite images of light at night (2025). 1 of them has skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Forêts National Park (21.77, Bortle 3), the brightest Reims (18.94, Bortle 7). Milky Way season in Grand Est runs May to July: on moonless nights the bright core stands clear of the horizon, climbing to about 13° at its highest.

19 Bortle class, 1 pristine to 9 city center park or dark-sky place city

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

NASA satellite night-lights map of Grand Est with every place marked

Darkest skies in Grand Est

  1. Forêts National ParkBortle 321.77

Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.

Brightest city skies in Grand Est

  1. ReimsBortle 718.94
  2. StrasbourgBortle 618.96
  3. NancyBortle 619.22
  4. MetzBortle 619.35
  5. TroyesBortle 519.55

All 10 places in Grand Est

Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.
Charleville-Mézières5Châlons-en-Champagne5Colmar5Forêts National Park3Metz6Mulhouse5Nancy6Reims7Strasbourg6Troyes5