YozoraAtlas

How dark is the sky in Viana do Castelo?

Sky darkness for 4 towns and parks in Viana do Castelo, 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 Peneda-Gerês National Park (21.05, Bortle 4), the brightest Viana do Castelo (19.57, Bortle 5). Milky Way season in Viana do Castelo runs April to August: on moonless nights the bright core stands clear of the horizon, climbing to about 19° 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 Viana do Castelo with every place marked

Darkest skies in Viana do Castelo

  1. Peneda-Gerês National ParkBortle 421.05

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 Viana do Castelo

  1. Viana do CasteloBortle 519.57
  2. Arcos de ValdevezBortle 520.04
  3. Ponte de LimaBortle 520.10

All 4 places in Viana do Castelo

Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.
Arcos de Valdevez5Peneda-Gerês National Park4Ponte de Lima5Viana do Castelo5