The day before yesterday, I observed sunset while flying over the eastern Mediterranean. After the sun set, it seemed to 'continue' in front of the horizon. I managed to snatch a picture (sorry for bad quality, my phone's camera kept focusing on the dirt on the window, rather than on the image of the sun).
Picture was taken at 17:44 local time (15:44 utc), at an altitude of roughly 34,000 ft. It took quite a while before the image entirely disappeared.
What exactly am I seeing here? Is this a mirage? Or is the reflection of the sun on a far-away piece of sea, where the sun is still over the horizon? The weather was mostly clear.
Another user adds this similar photo: