al·pen·glow | /ˈalpənɡləʊ/
If you’ve ever seen a snow-capped mountain lambent with a warm purple or pinky orange radiance set against a dusky sky, you’ve witnessed the wonder of alpenglow. It derives from the German alpenglühen, which, in keeping with exemplary Teutonic directness and a penchant for blends, literally translates as alps glow.
During the first stage of alpenglow at sundown, the sun appears to have set at sea level but still shines directly onto high elevations such as mountain summits. Because the shorter wavelength of blue light gets filtered out by the sunlight’s relatively long passage through the Earth’s atmosphere, the mountain tops glow with warm light. During the second stage, the sun has sunk further below the horizon and there’s no longer any direct sunlight on the mountains – now the tops are lit only by light reflected off particles in the Earth’s atmosphere. The alpenglow from this reflected light is far more subtle, casting no strong shadows and tending towards a duskier pink to purple. The sequence is of course reversed during sunrise.
There’s some minor controversy around whether alpenglow can be used to describe any instance of a warmly lit, glowing mountain top or if it refers only to the relatively muted effect of reflected, indirect sunlight. It seems unlikely that its original meaning was exclusive to the latter and, pedantry aside, this narrower definition certainly doesn’t reflect its common usage.
Closely related to alpenglow is the Belt of Venus phenomenon – a band of pinky orange light seen in clear, crepuscular skies – usually more prominent at sunset than sunrise. The pinky orange band is created by sunlight passing through the Earth’s atmosphere. Counter-intuitively, although the sun is setting, the sky at the horizon is darker than the pinky orange band above it. This darker blue area is caused by the shadow created by the curvature of the Earth.
Introduction Aeolian Alpenglow Apricity Asperous
Benthos Crepuscular Crispate Crown shyness
Desire lines Dreich Endragoned Edgelands
Frondescence Fumarole Gluggaveður Gossamer
Karst Komorebi Lawrence Long acre
Machair Monkey’s wedding Moonglade
Psithurism Quartz Rakuyou Roaring forties
Snag Soft estate Specular, diffuse and pellucid
Spoondrift Steam fog Swash zone Sylvan
Tellurian and thalassic Terracettes Uliginous