Noctilucent clouds on the northern horizon. This flight left Minneapolis for Rhineland, WI, and is almost a directly east flight. I just happened to glance out the window to catch this view, and watched as the formation peaked then broke up. I think sometimes people may think photos of night shining clouds are just clouds in the late sunset, but since these clouds are due North, and not towards the sunset at the aircraft's 6:00 position, I thought it may emphasize the geometry of the occurrence.
Very cool!!

Pixel 3 using night mode

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