How dark is the sky in Basque Country?
Sky darkness for 9 towns and parks in Basque Country, worked out from NASA satellite images of light at night (2025). 4 of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Valderejo Natural Park (21.32, Bortle 4), the brightest Bilbao (17.99, Bortle 8). Milky Way season in Basque Country runs April to August: on moonless nights the bright core stands clear of the horizon, climbing to about 18° at its highest.
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 Basque Country
- Valderejo Natural ParkBortle 421.32
- Izki Natural ParkBortle 420.98
- Gorbea Natural ParkBortle 420.74
- Aizkorri-Aratz Natural ParkBortle 420.63
Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.