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.
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Gillian
"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!"