Earth Season’s Fun Facts:
About a third of the world’s people live in latitudes between the tropics of cancer and capricorn
The changing seasons occur because the Earth, tilted on its axis, orbits the sun. Thus, the plane of the Equator is tilted with respect to the plane of the Earth’s orbit. Since the Earth is always tilted in the same direction, the latitude at which the sun appears directly overhead at noon changes as the Earth orbits the sun. The sun appears to follow a yearly pattern of northward and southward motion in the sky. If the equatorial plane and the orbital plane were the same, the sun would always be directly overhead at noon to an observer at the Equator, and there would be no change of seasons.
However, since the planes are tilted about 23° 30′ from each other, the latitude at which the sun appears directly overhead at noon varies throughout the year. Following centuries of tradition, astronomers divide the year into sea- sons according to equinoxes and solstices. The equinoxes occur when the Earth reaches the points in the orbit where the equatorial and orbital planes intersect, causing the sun to appear directly overhead at noon at the Equator. During equinoxes, the periods of daylight and darkness are nearly equal all over the world. One equinox occurs about March 21 . In the Northern Hemisphere, this is the vernal, or spring, equinox; In the Southern Hemisphere it is the autumnal. The other equinox, which occurs around September 23, is the autumnal equinox in the Northern Hemisphere and the vernal in the Southern.