How dark is the sky in Gotland?
Sky darkness for Visby (18.87, Bortle 7), so far the only place in Gotland on Yozora Atlas, worked out from NASA satellite images of light at night (2025). The bright core of the Milky Way never climbs clear of the horizon haze in Gotland while the sky is fully dark; the rest of the band passes overhead, with the longest moonless nights from October to March.
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
Darkest skies in Gotland
Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.
All 1 place in Gotland
Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.