YozoraAtlas

How dark is the sky in Connacht?

Sky darkness for 7 towns and parks in Connacht, 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 Achill Island (21.80, Bortle 3), the brightest Galway (18.68, Bortle 7).

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 Connacht with every place marked

Darkest skies in Connacht

  1. Achill IslandBortle 321.80
  2. Connemara National ParkBortle 321.79
  3. Wild Nephin National ParkBortle 321.79
  4. Slieve LeagueBortle 321.73
  5. the Ox MountainsBortle 421.64

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 Connacht

  1. GalwayBortle 718.68
  2. SligoBortle 619.10

All 7 places in Connacht

Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.
Achill Island3Connemara National Park3Galway7Slieve League3Sligo6Wild Nephin National Park3the Ox Mountains4