YozoraAtlas

How dark is the sky in Brittany?

Sky darkness for 7 towns and parks in Brittany, 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-Brieuc (20.44, Bortle 5), the brightest Rennes (19.00, Bortle 6). Milky Way season in Brittany 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 Brittany with every place marked

Darkest skies in Brittany

  1. Saint-BrieucBortle 520.44
  2. Saint-MaloBortle 520.23
  3. QuimperBortle 520.12

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 Brittany

  1. RennesBortle 619.00
  2. BrestBortle 619.29
  3. VannesBortle 519.80
  4. LorientBortle 519.90

All 7 places in Brittany

Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.
Brest6Lorient5Quimper5Rennes6Saint-Brieuc5Saint-Malo5Vannes5