When during a cloudless twilight, just after sunset (or just before sunrise) checking the opposite direction, a dark band rises upwards from the horizon (or sinks towards the horizon) which is the shadow of the Earth on the atmosphere. Just above this band, where the evening air is still lit, glows a pink band which is called the Belt of Venus. The pink arises from scattered and deeply reddened sunlight mingling with the deep blues of the eastern sky.

The picture was taken just after sunset with a rising darker band & Belt of Venus in the SE.