ONR Science & Technology Focus
               Oceanography       Space Sciences       Blow the Ballast!       Teachers' Corner   
Observing the Sky Solar System Satellites Navy Research Resources

Observing the Sky: Motion of the Earth - Rotation

From Earth, we see the Sun rise, move across the sky, and set. The stars do the same each night. All of this apparent motion makes it easy to forget that the Sun and stars aren't really moving at all. They only seem to move because the Earth is constantly rotating, or spinning, carrying us in and out of view of the Sun and stars.
The view from Earth is a bit like the view from a moving car. Looking out a side window you see trees and houses passing by. Now imagine that car is going in a circle. You pass the same scenery over and over again. We are all passengers on the surface of the rotating Earth and it carries us past the Sun, day after day.

 

The Earth rotates around the axis, an imaginary line through the center of the planet. The axis connects the North and South Poles like an axle connects the wheels on a car. As the Earth spins on its axis, we are carried in and out of the sunlight that is always shining on half the planet. When one side of the planet has day, the opposite side has night. The Earth's axis does not point straight up and down, but is tilted 23.5'. This means that different places pass through different amounts of sunlight and darkness each day.

Why is East on the left? You probably learned your directions by facing North, with East on your right, West on your left, and South behind you. So why do our graphics show East on the left? Because we are showing you the view looking South. In the Northern Hemisphere, most of the action takes place in the southern sky, with the Sun, Moon, and planets following similar paths across it.
next page