Alpenglow - originally a translation of the German Alpenglühen, with the Norwegian variant alpeglød in occasional literary use - is the rose, amber and pink light that washes over high mountain faces in the brief minutes just before sunrise and just after sunset. The optical phenomenon is caused by sunlight refracting through the lower atmosphere when the sun is geometrically below the horizon - the longer wavelengths (red, orange, pink) are scattered less by the dense air than the blue end of the spectrum, and the resulting light bathes the high faces in a color that the camera struggles to capture and the eye remembers for years.
Norwegian mountain country produces unusually pure alpenglow conditions. The combination of clean sub-Arctic air, the long shallow angle of the sun in spring and autumn, and the high vertical relief from sea-level fjord to 1,500-meter peak gives the mountains a roughly twenty-minute window of saturated color at dawn and dusk that rarely repeats elsewhere. The classic example is the wall of Trolltindene above Romsdalen on a clear October evening; the granite turns the color of old copper for fifteen minutes and then fades back to grey.
For the photographer, the alpenglow window is the most-discussed planning variable on a Norwegian mountain trip. For the walker, it is one of the small recurring rewards of being in the right place at the right hour - on the summit at dusk, on the eastern face at dawn, on the cabin terrace with a coffee while the light shifts.