The motion of a satellite around earth is defined by Kepler's Laws of Motion. So, to better understand the GOES and POES observations, we need to review these laws. The physics of any object in orbit about a more massive body is best explained by Kepler's laws of motion:
- The path of the object will be an ellipse, with the massive
body at one focus.
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An ellipse contains two foci.
The Earth occupies one focus of the ellipse, not the center. |
- A straight line joining the central body and the orbiting body
will sweep out equal areas in equal times.
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Satellites do not orbit at a constant speed -- they speed
up and slow down. The time between points A and B is the same
as the time between points C and D. The areas of the two wedges
are the same. Does this work for earth's orbit? Count the number of days between September 21 (Autumn Equinox) and March 21 (Spring Equinox) and the number of days between March 21 and September 21. |
- The square of a planet's year always equals some multiple of the cube of the planet's distance from the sun.
These relations are true for any orbit: a planet orbiting a star, a moon orbiting
a planet, or an artificial satellite orbiting the Earth.
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