Each evening, shortly after sunset,
darkness covers the land.
Having mystified thinkers for millennia,
the mechanism for this occurrence
has now been identified: migration.
Darkness, it has been found, is composed
of an almost infinite number of particles,
which roost and reproduce up north
where they have fewer natural enemies:
Forest fires, lampposts, lasers, blazing sunlight,
torches, candles, lighthouses, limelight, and electricity
are relatively rare in the polar regions.
from: The Alchemy of Stars. Copyright 1979.