How is it produced?

By the sun's refraction--that is, the variation of the rays of light
from their direct course, occasioned by the difference of density in
the atmosphere.

_Variation_, change.

_Density_, closeness of parts, compactness.


What is the poetical name for the morning Twilight?

Aurora, the goddess of the morning, and harbinger of the rising sun:
whom poets and artists represent as drawn by white horses in a
rose-colored chariot, unfolding with her rosy fingers the portals of
the East, pouring reviving dew upon the earth, and re-animating plants
and flowers.

_Harbinger_, a forerunner.

_Portals_, gates, doors of entrance.

_Reanimating_, invigorating with new life.


What remarkable phenomenon is afforded to the inhabitants of the polar
regions?