How dark is the sky in Slovenia?
Sky darkness for 21 towns and parks in Slovenia, worked out from NASA satellite images of light at night (2025). 6 of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Triglav National Park (21.41, Bortle 4), the brightest Ljubljana (18.81, 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
Darkest skies in Slovenia
- Triglav National ParkUpper Carniola · Bortle 421.41
- Goričko Nature ParkMura · Bortle 421.24
- Planina Polje Landscape ParkLittoral-Inner Carniola · Bortle 421.11
- Rakov Škocjan Landscape ParkLittoral-Inner Carniola · Bortle 421.11
- Udin Boršt Landscape ParkUpper Carniola · Bortle 420.70
Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.
Darkest place in each region of Slovenia
| Region | Places | Dark places Bortle 1 to 4 | Darkest place |
|---|---|---|---|
| Central Sava | 1 place | 1 dark | Trbovlje20.56 · Bortle 4 |
| Central Slovenia | 3 places | 0 dark | Kamnik20.11 · Bortle 5 |
| Coastal-Karst | 2 places | 0 dark | Izola19.90 · Bortle 5 |
| Drava | 2 places | 0 dark | Ptuj19.83 · Bortle 5 |
| Gorizia | 1 place | 0 dark | Nova Gorica19.55 · Bortle 5 |
| Littoral-Inner Carniola | 2 places | 2 dark | Planina Polje Landscape Park21.11 · Bortle 4 |
| Mura | 2 places | 1 dark | Goričko Nature Park21.24 · Bortle 4 |
| Savinja | 2 places | 0 dark | Celje19.86 · Bortle 5 |
| Southeast Slovenia | 1 place | 0 dark | Novo Mesto19.94 · Bortle 5 |
| Upper Carniola | 5 places | 2 dark | Triglav National Park21.41 · Bortle 4 |