Aurora towns ranked by December darkness

The widest gap between neighbours falls between Anchorage and Seattle, 2.0 h. 2 neighbouring pairs sit within 0.1 h of each other (Seattle and Duluth; Portland, Maine and Buffalo), close enough that their order means little.

December's order follows map latitude exactly, because night length depends on the sun, not on the magnetic field. Tromsø, the farthest north at 69.6 degrees, leads. The five lower 48 towns trail with about 14 hours each, a narrow spread because they sit within about 5 degrees of latitude of one another.

Civil night overstates usable darkness at the top of the list. Near the solstice the sun does not rise at Tromsø, yet midday stays in civil twilight, and part of the long night sits between -6 and -18 degrees. The note column gives astronomical night, the strictest measure, for each town, and the month pages list every night of December.

How to use it. December gives the most hours to wait for activity, which helps most when you sit close to the oval and activity is modest. At Tromsø civil night lasts more than 19 hours on the 15th, so SWPC's 10 PM to 2 AM window sits deep inside the dark on every night of the month. In the lower 48 the extra hour or two between towns matters less than the storm level. The December hub lists each town's first and last night of the month.

Limits. The figures are computed for the coming December 15 at each town's coordinates, from local noon to the next noon, with SunCalc's standard refraction. They ignore terrain, which can hide a low sun or moon, and city light, which brightens the sky long after twilight ends. Cloud is not part of this ranking; each town page gives NASA POWER's December cloud average beside the darkness.

The order follows map latitude from north to south.

December nights are the longest of the year, so this ranking shows how much time each town gives you to wait for activity. It says nothing about storms; SWPC favors the equinoxes for those.

Hours with the sun at or below -6 degrees on the night of the coming December 15, from local noon to the next noon, computed with SunCalc at 5 minute steps. The note gives astronomical night, the sun at or below -18 degrees, for the same night.

For your own coordinates, use the dark hours calculator. The background is in how dark does it need to be?, and every threshold is listed on the methodology page.