I'm going to Greenland this August on a 16-day Princess cruise. I hope to be able to post a live thread on the Princess board during my cruise. I did not book my cruise until last week. All of the excursions through Princess are sold out. I plan to study up a bit on the ports and walk a lot to see some of the highlights in each. The three Greenland ports on my cruise are Nuuk, Nanortalik, and Qaqortoq.
By August 24 and 25, when my ship will be in the last two Greenland ports, the sun will set around 8:30 p.m. and rise around 5:30. But civil twilight, nautical twilight, and astronomical twilight continue for several hours. There's just a brief period between 12:15 a.m. and 2 a.m. of true night--where the sun is at least 18 degrees below the horizon. I plan to look at the aurora forecast on this website before and during my cruise: https://www.gi.alaska.edu/monitors/aurora-forecast
One of the participants on the roll call for my cruise posted the port guides from her cruise three years ago. It's on this page: https://boards.cruisecritic.com/topic/2765243-caribbean-princess-august-15-2022-nyc-canada-greenland/page/36/