YozoraAtlas

How dark is the sky in Ulster?

Sky darkness for 3 towns and parks in Ulster, worked out from NASA satellite images of light at night (2025). 2 of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Glenveagh National Park (21.58, Bortle 4), the brightest Letterkenny (19.26, Bortle 6).

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 Ulster with every place marked

Darkest skies in Ulster

  1. Glenveagh National ParkBortle 421.58
  2. InishowenBortle 421.28

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 Ulster

  1. LetterkennyBortle 619.26

All 3 places in Ulster

Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.
Glenveagh National Park4Inishowen4Letterkenny6