One of the most familiar reminders of the passage of time is the continuous cycle of day and night. As you know, the sun's apparent motion in the sky is caused by the earth's rotation. The earth completes a rotation (with respect to the sun) once every 24 hours.
For observers on the side of earth closest to the sun it's noontime, or close to it. On the other side of the earth the time is midnight — people here are in the darkness of the earth's shadow. So for a given observer, the local time depends on his or her location and the current orientation of the earth.