I was extremely lucky to spot this on a flight a few years back. I've never seen anything like it. I imagine it's very rare.
As you can see, the sun is actually under the horizon of clouds even though it's still above the ground. This photo also illustrates the curvature of the earth very well. It makes sense if you imagine the earth as a not so large ball surrounded by an atmosphere and the sun behind it, incredibly far away.
This was before my phone had a camera so, I was extra lucky that my digital camera was in my hand luggage.
Here's the other photo I managed to take of it: