Some images of sunset.
It is the pink to brownish border between the dark shadow band of Earth
and the sky above.
You can see it at the sunset, by looking towards East, when the atmosphere is cloudless, yet dusty.
The shadow of the Earth is seen as the dark blue part of the sky, and the red light of the Sun, backscattered by the particles of the air, which forms the belt itself.
These three pictures have been taken 10 minutes apart, showing the progression of the shadow of the Earth.
Panoramas of 3 or 4 pictures taken with a Canon Rebel 300D, and an zoom lens 18-55mm.