: During orbit, the Earth's poles are constantly tilted at an angle of 8.5 degrees to the orbit of the pole. The equator is tilted 23.5 degrees along the plane of the equator. Generally, day and night are equal in all parts of the world on 21st March and 23rd September. Notice in the figure , these two days the north and south poles are at equal distances from the sun. And so no northern or southern hemisphere gets more or less sunlight than each other. (Concentrate on the figure) This day is therefore half day of 24 hours where day and the rest are night. These days the sun's rays fall at an angle of 90 degrees to the equator , 7.5 degrees to the North Pole and the Antarctic, and 0 degrees to the poles. Before 23rd September, 21st June, the North Pole of the Earth is most inclined towards the Sun and the South Pole is farthest away. From the next day the North Pole moves and the South Pole approaches. Thus on 23rd September the two poles come at equal distances. This is called autumnal equinox . Again, before March 21, on December 22, the Sun is tilted most towards the South Pole and farthest from the North Pole. From then on it moved again from the South Pole and towards the North Pole on March 21 and came at equal distances from the two poles. This is called vernal equinox .