Physical Effects of the Earth's Rotation (Coriolis Effects) As the Earth rotates to the East, any object not attached to it will seem to drift to the West. This is why the stars, Sun, Moon, and planets all rise in the East, and set in the West. Their motion is, in a sense, an optical illusion, a mirror image of the motion which we actually have. Similarly, there are effects which act on objects near the surface of the Earth, which are not so obvious as the rotation of the sky, but which can be directly verified by careful observation. These effects can be explained in terms of an 'imaginary' force, called the Coriolis force (after Gustave Coriolis, an 18th-century French mathematician who explained the effect in an elegant mathematical way), and as a result, the effects are referred to as Coriolis effects.
The nature and size of the Coriolis effects depend upon where you are. If you are near the Pole, the axis of the Earth's rotation is nearly vertical relative to your Horizon, and as things spin around in the sky, they move nearly horizontally. Similarly, the Coriolis effects are almost completely horizontal. But if you were near the Equator, where the Earth's axis of rotation is nearly horizontal, things spinning around the sky would move nearly vertically, and the Coriolis effects are almost completely vertical. At in-between latitudes, the stars rise and set at an angle to both the vertical and the horizontal, and there are both vertical and horizontal Coriolis effects. In general, as you move toward one of the Poles, the horizontal Coriolis effects grow, and the vertical ones shrink, whereas if you move toward the Equator, the horizontal effects shrink, and the vertical ones grow. | |
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