Brocken Spectre

I've never seen anything quite like this before.
I took the photo from the plane window, just as we were approaching Iceland... I didn't even see the shadow of the plane at the time; I thought it was some sort of circular rainbow.

It happens when you are looking down upon mist or fog - or, in this case, clouds - with the sun behind you... you see your own shadow - or, as it happens, that of the plane from which you are taking your photo - apparently much magnified, surrounded by what is known as a glory, which is basically refracted light.
It's called Brocken spectre because the Brocken is where it was described, and where legends have arisen around it.

Fascinating!