Which nights this month are best, ignoring solar activity?

Tromsø over the same 30 nights: the top three are Mon Oct 19 (4 h), Sun Oct 18 (4 h), Sat Oct 17 (4 h). The minutes are civil night with the moon below the horizon between 22:00 and 02:00 Europe/Oslo time.

Ties are common when several nights keep the whole 4 hour window dark and moonless. Glow breaks them on total moon-free dark minutes across the night, then on date.

Each night starts at local noon on its date. Glow samples the sun and moon every 5 minutes and counts the minutes between 22:00 and 02:00 local time when the sun is at or below -6 degrees and the moon's center is below the horizon. That count is the score, from 0 to 240.

The window comes from SWPC's viewing tips, which place the best aurora within an hour or two of midnight. Glow uses the window exactly as published, in local clock time.

When two nights tie, the one with more moon-free civil night across the whole night ranks higher. A remaining tie goes to the earlier date.

The aurora depends on the solar wind reaching Earth. SWPC's OVATION product forecasts 30 to 90 minutes ahead, the time the solar wind takes to travel from the L1 monitoring point to Earth. A 30 night ranking cannot include a number that does not exist yet.

So the ranking answers a narrower question: on which nights will the sky be darkest during the hours SWPC recommends, if the aurora shows? That part is known weeks ahead.

Book or plan around the top of the list, then watch the live tools as the night comes. The chance tool reads your OVATION cell and US cloud, and the southern edge tool shows how far the oval reaches.

In summer at high latitudes the list can be all zeros, because the 22:00 to 02:00 window never gets civil-dark. The verdict says so rather than ranking empty nights.