Lunar Phase Simulator – Background 3
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.
The stickfigure in the interactive diagram below represents a North American observer. The view is from directly above the North Pole. Click and drag on the earth or stickfigure to rotate the earth around its axis. In the upper right the corresponding local time for that position is displayed.
You'll notice that sunrise and sunset in the diagram are always at 6:00 am and 6:00 pm. This simplification glosses over the seasonal changes caused by the earth's tilt.