Northern lights, Tromso

No chance.

Sorry, much too early.

Depends on solar activity.

AFAIK, northern lights occur most frequently from January to March, and they are more likely to be spotted the further to the North you go.

#3, the solar activity doesn't matter squat with 15+ hours of daylight (plus extended dusk and dawn) in early september.

I thought sun set at 6pm in Sept

Forgot about long twilight there!

I thought sun set at 6pm in Sept. Forgot about long twilight there!

Everywhere in the world there are 12 hours of daylight at the Autumn equinox which occurs on 22 or 23 Sept. The point is that at Tromso, there can be 12 hours of daylight on 23 Sept but 15 hours of daylight on 1 Sept, because it is transitioning from 24 hours daylight on 26 July to 0 hours on 26 November, ie, the amount of daylight changes by an average of almost 5 hours a month, and it changes fastest around the equinox.

As you say, additionally there is longer twilight at higher latitudes.

Clearly there is some complete "astronomical" darkness when the night is 9 hours long, probably the central 4 hours or so is "astronomically dark" at that time. But seeing the northern lights in such conditions requires either a rare and strong display, or else being up in the small hours when it is dark enough, and hoping the lights occur in that narrow window of sufficent darkness. Whether there is a bright moon shining also makes a difference.

Yes moon is bad. I've never seen it in September though, that's not possible.

I've seen the aurora borealis in August. The chances aren't good, but not nonexistent either.