earth is the third nearest planet from the sun and fifth largest planet of the solar system. the earth revolves around the sun once year. rotating once on its axis. the obliquity of the earth is 23.5 degree. obliquity is the angle between a planet's equatorial plane and its orbital place. different seasons and diverse weathers are caused by the tilt of the earth as it moves around the sun. because of the tilt, the north pole faces the sun between march and September. this is the warm season for the northern half on our planet. the south pole faces the sun between September and march. this is the warm season for the southern half of our planet. 
the length of the day and night is equal in the spring and autumn equinoxes at the equinoxes at the equator. the length of the day varies about 14 to 10 hours at 30 degree. latitude and about 16 to 8 hour at 50 degree latitude. September 21 is also a special day near the south pole.
there are four season on the earth. they are autumn, winter, spring and summer. summer occurs when a hemisphere faces the sun, and winter occurs when a hemisphere is tilted away from the sun. the north pole has total daylight and the south pole has total darkness in summer solstice. the opposite occur in winter solstice. the length of day and night is almost equal at the equator throughout the year.
in general, the summer and winter temperatures get lower the further away from the equator. the temperature remain high at the equator throughout the year because the sun is always striking there. hence, is no seasonal variation at the equator.
at the south pole, the sun comes up for the first time in six months and remains dark from June 21. winter at the north and south poles means dark nights that all day long. similarly, it is 24 hours day light at the poles during summer.