I'm posting my PM to Bill for the potential future benefit of others too:
Hi Bill. Fairbanks is an excellent place to go and Chena Hot Springs Resort caters to aurora viewers with a special coach tour. march is also a great time to go, not only for the aurora but also for other fun things to do in Fairbanks including the Int'l Ice Art Championships and the Open North American Championships (sprint) sled dog races.
I've written a number of travel journals on my two trips there in March 07 and again in March 08. Here are the direct links to some readin info you might find helpful in your planning:
http://www.igougo.com/journal-j65217-Fairbanks-Exploring_Fairbanks_Winter_Wonderland.html
http://www.igougo.com/journal-j65218-Fairbanks-Indoors_in_Fairbanks.html
http://www.igougo.com/journal-j65220-Fairbanks-Alaskas_Interior_Region.html
http://www.igougo.com/journal-j70410-Fairbanks-Back_to_Nature_-_Fairbanks_AK.html
As for September, the theory is that it's close to the equinox (as is March) so that helps. Fall brings more moderate climates (it can be below zero for days/weeks in Fairbanks in March!). I believe there is longer daylight, however in September, but I'm not 100% certain how much more.
I will be in Fairbanks this year in mid September and looking forward to seeing how much of the aurora is viewable.
There's a lot I could write about aurora viewing in Alaska, but need to dash off to work. Feel free to write me for more info as you begin your planning.
The sun has been in a "solar minimum" for about two years now, making the aurora viewing hit and miss, although the past couple of weeks seems to have seen increased activity. I've seem some beautiful photos coming from up there.
If you haven't already, I would encourage you to check into TripAdvisor (
www.tripadvisor.com) and go to the Alasks forum. I post frequently there regarding the aurora (and other stuff on Alaska).
Best wishes to you in your planning.
Von