h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I just happened to notice that the article says that the Moon is a natural sattelite of earth. That isn't true, as we all know the moon is too large, was created by an impact, and is beyond the distance for a sattelite. It just appears to orbit the earth due to its odd solar rotational pattern. Admittedly this is effected by the earth's gravity, but it just isn't a sattelite of earth, it is a 'companion planet' which orbits the sun in such a way as to have the same 'face' toward the earth at all times and it slows and accelerates in such a way as to make it appear to be 'in orbit' about the earth.
sorry for all you romatics, but there it is.

Sorry, Ancient_Magician, but astronomers are unanimous in agreeing that the moon is a satellite of the earth and does in fact orbit around it.

From Wikipedia: "The Earth–Moon system is sometimes considered to be a double planet rather than a planet–moon system. This is due to the exceptionally large size of the Moon relative to its host planet; the Moon is a quarter the diameter of Earth and 1/81 its mass. However, this definition is criticised by some, since the common centre of mass of the system (the barycentre) is located about 1,700 km beneath the surface of the Earth, or about a quarter of the Earth's radius. The surface of the Moon is less than 1/10th that of the Earth, and only about a quarter the size of the Earth's land area (or about as large as Russia, Canada, and the U.S. combined)."
While some consider the debate to be closed, it remains true that the 'classical' definition of a moon doesn't include the one 'orbiting' the earth.

Which just goes to show that you can't trust Wikipedia.

By simple mechanics, no free body can orbit around another moving free body. Moon is a free body and the earth is a moving free body.

Oh yes it can!

Try running around a friend, who is walking in a straight line. Distance between you and your friend should be of constant magnitude. Now trace your path and see if it makes a closed geometrical figure.
If what you say is correct, your path should be circular around your friend.

The earth and the moon orbit together around a point called the Barycentre. Because the earth is much bigger than the moon, the centre of the earth is much closer to the barycentre than the centre of the moon is. In fact, the barycentre is actually within the Earth.

This is the same for any orbit. If a pebble orbits around a star, then the star's position is affected by the pebble's gravity and the star orbits around a barycentre, as does the pebble. In this case, the barycentre is probably micrometres at most from the centre of the star.

Relative to the earth, the moon moves in a circle (approximately) around it. Relative to the solar system, the moon moves in a sort of epicycloidal path around the sun.

The moon is orbiting the earth because that's what "orbiting" means.

Consider a moving Barry center. What will be shapes of related bodies' orbital paths? It is only with a static Barry center, related bodies may appear to move in circles.
Although earth-moon system was much easier to observe than sun-planet systems, Kepler avoided mentioning earth-moon system in his laws on planetary motion. This is because, with a moving earth, laws on planetary laws (in total) could not be applied to earth-moon system. For 'Kepler's laws on planetary laws' to be true they require a static central body (static sun in space).

In the case of moon, you are right. It moves in a wavy path about earth's orbital pah, periodically moving to the front and to the rear of earth. This is because the earth is a moving body. The same logic should apply to all (planetary) orbital paths about moving central bodies. The sun is also a moving body.
Laws on planetary orbits were derived from observations of planets' relative positions with respect to sun. Therefore they will give accurate predictions of relative positions of all bodies in an orbital system. However, it is incorrect to belief that these laws are infallible, when applied to other parameters of concerned bodies.

>>it is incorrect to belief that these laws are infallible, when applied to other parameters of concerned bodies.

The laws of planetary motion are among the best-known and most infallible laws in physics. I'm not sure exactly what point you are making in these posts.

Precession of orbital path, pioneer anomaly and flyby anomaly are few examples. An infallible theory should not give rise to anomalies.

The word anomaly, in those examples, does not mean what you think it does. In orbits, it means an angle: the angular distance of a planet or the moon from its last perihelion or perigee.