Question

Why is there an absence of sunlight on the Earth's polar regions for long periods of time during the winter months?

Answer 1

Because the earth’s axis is tilted.

Explanation:

The pole is in darkness during winter because the earth is spinning at a 23 degree angle to the sun.

A diagram will make this much clearer:

Taken from: nasa.gov/sites/default/files/thumbnails/image/axis_png

You can see no matter how the earth spins, the South Pole will not come into the sunlight as during winter the South Pole is pointing away from the sun due to the tilt of the earth’s axis. The situation is the same for the North Pole during their winter.