Hello there - the Northern lights, weather permitting, are visible from November - February and best viewed from Tromso. Regular cruise ships do not sail this route at this time of year but the Hurtigruten runs the Norwegian Coastal Voyage daily throughout the year and calls at Tromso but only for a few hours. If you want to see the Northern Lights and the fjords may I suggest that you consider two different trips - perhaps a long weekend in the Winter for the lights, followed by a Spring/Summer cruise to the fjords. I say this because the lights are only visible during the aforementioned months during the Polar nights period, whilst the fjords are at their best when the days are longer and the light is good; in the winter some of the fjord hamlets only have 2-4 hours of daylight making sightseeing virtually impossible. Hope this helps.
Regards - Janet.
Google is a wonderful thing......When is the best time to see the Northern Lights?
Usually during the darkest period which is between November and February, although they can be seen as early as late August and as late as mid April.