One of the most beautiful signs of Nature I have ever seen.
I was on Lake Kelowna, BC, which is about as far South as you can get in Canada. I was attending a retreat at an Anglican Christian Camp by the side of the lake. Amenities were primitive to say the least! No air conditioning, no glass windows (only torn mosquito netting), no bedding in the huts. The weekend started hot and humid with plenty of mosquitoes!
Fortunately, the air cooled and a breeze came in from the lake, so the next two days were quite pleasant. On the Sunday evening we were seated round the camp fire beside the lake, and at around 10:30pm the nigh sky began to take on a grey glow, as if one was looking at the sky over a city. The grey turned to green, and half an hour later hung in curtains above us. It was an awe-inspiring sight!
One of the people present had a decent camera, and despite camera shake - trying to take a dim light at night - did a remarkable job of capturing the night sky.