How dark is the sky in Wisconsin?
Sky darkness for 28 towns and parks in Wisconsin, worked out from NASA satellite images of light at night (2025). 16 of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Apostle Islands National Lakeshore (21.85, Bortle 3), the brightest Milwaukee (17.12, Bortle 8). Milky Way season in Wisconsin 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 Wisconsin
- Apostle Islands National LakeshoreBortle 321.85
- Big Bay State ParkBortle 321.78
- Chequamegon-Nicolet National ForestBortle 321.74
- Copper Falls State ParkBortle 421.69
- Newport State ParkBortle 421.64
Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.