Answer:If you're asking why are days getting shorter and nights longer, its due to the earth's position in orbit around the sun, and the earths tilt.
Explanation: The earth's tilt is at 23.5 degrees. During the December Solstice (solstice being when the earth is either at its most northern side in orbit, or more southern side in orbit)
the northern hemisphere would be leaning most away from the sun for that year, which also causes seasons, and after the winter solstice the days then get longer and nights shorter.