Diurnal and annual motion of the earth

The earth move round on its axis as well as in its orbit around the sun.The motion of the earth on its axis is called diurnal motion and a complete round on its axis is called a rotation.The earth takes about 24 hours (23 hr 59 min and 4.09 s) to complete one rotation.The motion of the earth in its orbits is called annual motion and a complete round around the sun is called a revolution.The revolution of the earth has a direct concern with the change in seasons and varying length of day and night.The rotation of the earth causes day and night on the earth.The earth takes about 365 days (365 days, 6 hr, 9 min and 9.54 s) to complete one revolution.
The axis of the earth is inclined to the plane of ecliptic at an angle of 66.5 degree.It causes different seasons and varying lengths of day and night.If the axis were perpendicular to this plane,all parts of the earth would have equal day and nights at all times of the year.

Day and night: an effect of the rotation of the earth

Day and night on the earth occur due to its rotation.when the earth rotates on it axis,only one portion of its surface faces the rays of the sun and experiences day.The other portion which is always from the sun's ray will be in darkness which experiences night.
To understand better about the cause of day and night, place a globe or ball as  the earth in a dark room and use a flash of light or a table lamp representing the sun. Do you see all the parts of the globe facing light?
When the earth rotates eastwards,every part of the earth's surface will be exposed to the sun at some time or the other.The part of the earth's surface that emerges from darkness into the sun's rays experiences sunrise.Later, when it is gradually obscured from the sun's rays,it experiences sunset.