Obliquity of the ecliptic.

The earths tilt is 23.5 degrees, which is an oblique angle, the earth is also spinning 23.5 degrees away from the perpendicular. The obliquity of the ecliptic is the angle between the axis of rotation of the earth and the ecliptic plane in which the earth rotates the sun. The angle varies between 22.5 to 24.5 degrees. It takes an average of forty one thousand to complete the obliquity cycle. The earths tilt is what causes us to have our seasons.