At two poles the sun stays above the horizon for 6 months and below the horizon for 6 months. In the latitudes farther from the poles, the night and day are not exactly as we feel day and night , much like twilight. The main reason for this is that the earth is tilted 23.5 degrees with the sun. When at any pole: From 21st March to 23rd September, there are continuous days at North Pole for six months and continuous night at South Pole. The reverse happens from 23rd September to 21st March, which means 6 months continuous day at the South Pole and night at the North Pole. This means that March 21 and September 23 are the two marginal dates for changing the day and night in the poles. These two days both poles are equally far from the sun. Day at the North Pole: After March 21, the North Pole tends to lean towards the sun. The maximum amount of inclination is on 21st June. After June 21, the North Pole began to move away from the sun. It moves at a distance equal to the South Pole from the Sun on 23 September. During these six months the sun is at the north pole (literally in the polar circle) above the horizon. So give it a go. On the other hand, this time it is night because it is located below the south polar horizon. Day at the South Pole: The North Pole moved away from the Sun on September 23 and reached the same distance as the South Pole. This time he is moving more. Thus, on December 22, the North Pole is farthest from the Sun and the South Pole is closest. Now it's time to move to the South Pole again. The south pole moves and the north pole again decreases the distance. Thus, on March 21, the two poles are equally far from the sun. As a result , these six months are day at the South Pole and night at the North Pole.