Need advice from Norway experts
 

I am just getting started researching a trip to Oslo to take place in early October. I will likely have less than a week. If I want 2-3 days in Oslo, plus I want to see fjords, how many days should I consider the minimum for this trip? Is there any chance I could get far enough to see northern lights within a week time frame? I am a rather leisurely traveler, but I don't want to miss an opportunity--this will be a work trip for the spouse, and we can rarely afford Scandinavia on vacation otherwise. Thanks in advance for any guidance!

The Norway in a Nutshell (Oslo to Bergen) package will give you a taste of the fjords.

Yorkshire

If the Northern Lights are your main priority it may be worth taking a cheap Norwegian air flight to Tromso. Due to the earth's magnetic field it is one of the best areas to see the lights. We stayed there over New Year and had three nights of an incredible show. Tromso is a lovely place well worth a visit.

October is just about "in season" for the lights.

thanks--though I would like to perhaps move up the coast to Tromso and fly back to Oslo, it looks like I will probably need to decide on either the northern lights or the fjords with a week time frame (or extend the trip, which is unfortunately probably not in the cards).
We do a lot of nature/outdoor travel but rarely in a cold climate, so I like the idea of seeing the NL in October.
Once DH and I narrow down a time frame and do more research, I'll be back.

We went late September last year and saw the Aurora. As long as there is darkness there is a chance you can see them. Tromso is geared up for aurora spotting.
Spend a couple of days in Oslo, fly to Tromso for a couple of nights, then fly to Bergen, NIN back to Oslo.

Norway-in-a-Nutshell will be a good trip to the fjords (google it). The NIN trip can be done in one day - if you leave early. Or, I went halfway and spent the night, returning to Oslo. Or if you have the time go Oslo to Bergen and spend 1 or 2 nights and return to Oslo. Or do your return flight out of Bergen.
NIN is not the only way to see the fjords by any means but in a short trip, I believe it to be the most efficient.

And to me, Oslo deserves 3-5 days. I'm sure others do it faster and maybe less thorough, but at my age, I didn't assume I was going to return so I wanted to see it ALL (there are still too many unseen places!).

Unfortunately, aurora boreallis do not perform on schedule! It will be the luck of the draw! EVEN if you persued a flight further north to increase your chances, they may not happen.

I really liked Oslo and Norway. I hope you do also.

Don't forget that every transport leg, even with flight eats up most of a day. If you have limited time then stick to one place - the Northern lights are finicky, you need several nights in Tromsø to have a reasonable chance of a good display. There are also plenty of things to do there.
October is already out of season for the fjords (though still possible - but chance of poor weather is high and days getting shorter). Save Oslo and the fjords for a summer holiday.