Alpenglow is the pink light on mountains and high walls facing away from the sun just after sunset, lit by the sky rather than the sun.

The true alpenglow comes after the sun is below the horizon: the eastern faces are lit by light scattered back from the still-sunlit sky in the west, which is why it is pink rather than gold and why it fades from the bottom up. The gold on the same peaks a little earlier, while the sun is still up, is ordinary low sunlight.

The peaks glow after the valley is dark because they are lit by the afterglow itself, reflected down.