At the 74° parallel north, the midnight sun lasts 99 days and polar night 84 days, while the respective figures at the 81° parallel north are 141 and 128 days.   

In Longyearbyen, midnight sun lasts from 20 April until 23 August, and polar night lasts from 26 October until 15 February.

I would love to visit Longyearbyen, but that will never happen. However, I remain fascinated by this place.