How dark is the sky in Ireland?
Sky darkness for 42 towns and parks in Ireland, worked out from NASA satellite images of light at night (2025). 20 of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Mizen Head (21.86, Bortle 3), the brightest Dublin (17.63, Bortle 8).
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 Ireland
- Mizen HeadMunster · Bortle 321.86
- the Kerry Dark-Sky ReserveMunster · Bortle 321.83
- Sheep's HeadMunster · Bortle 321.83
- Achill IslandConnacht · Bortle 321.80
- Connemara National ParkConnacht · Bortle 321.79
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 province of Ireland
| Province | Places | Dark places Bortle 1 to 4 | Darkest place |
|---|---|---|---|
| Connacht | 7 places | 5 dark | Achill Island21.80 · Bortle 3 |
| Leinster | 17 places | 3 dark | the Slieve Bloom Mountains21.32 · Bortle 4 |
| Munster | 15 places | 10 dark | Mizen Head21.86 · Bortle 3 |
| Ulster | 3 places | 2 dark | Glenveagh National Park21.58 · Bortle 4 |