Beautiful picture of 'noctilucent clouds' - APOD 18th July: http://apod.nasa.gov/apod/ap060718.html
But here on the coast of North West England it's not too unusual to have clouds under lit from a Sun below the horizon. We look out due West and ducking under Greenland the next bit of dry land is the North end of Newfoundland. When there is cloud cover over the land, but none out to sea, the set Sun shines on the under side of the clouds.
I was regretting yesterday that I had no pics - and tonight it's there!
Not the greatest picture or the most dramatic display, but these are rather lower 'noctilucent' clouds. Taken tonight, 2140 BST, looking due West.
JOhn