I tried Googling "etymology midnight sun"; the second thing that comes up is one of my own posts in the ATM section of this very board. Nothing useful came up, so far as I can tell, and I don't think any of my books have an answer as to how old the expression is. But again, it long predates polar exploration.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"