It's gonna be tough to do a Alaskan cruise and see the Northern Lights on the same trip. Their big Cruise season is May till mid - September , that's outside Northern Light viewing season.
We went in '17 on the rail tour through Princess Cruise lines, but didn't go via a cruise. We flew into Fairbanks and worked our way back to Anchorage, spending 8 days in AK . We went last week of August and did a lot of tours . Princess has their own rail cars made for viewing , you just click along about 40 MPH and see the scenery. When we went into Denali the leaves were turning and we saw A BUNCH of wildlife . The Moose were sheading velvet.
I can't speak for a cruise , however, if you go to Alaska and do a cruise only , you've missed Alaska. I don't care much for Whales and icebergs. You could spend 2-4 weeks up there and still only hit the high spots. One of the few places I've been that I want go back to, we plan on going back soon.


"Why do you ask"?

Too many people spend money they don't have , on things they don't need, to impress people they don't know.