The Collaborative International Dictionary of English v.0.48:

Alpenglow \Al"pen*glow`\, n.
   A reddish glow seen near sunset or sunrise on the summits of
   mountains; specif., a reillumination sometimes observed after
   the summits have passed into shadow, supposed to be due to a
   curving downward (refraction) of the light rays from the west
   resulting from the cooling of the air.
   [Webster 1913 Suppl.] Alpenhorn