wrote:
The post is duplicated at this address.
http://members.optusnet.com.au/maxkeon/sun-merc.html
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Perihelion Advance Of Mercury.

In the Sun-Mercury closed gravitating system, from the viewpoint
of the Sun, Mercury is oscillating back and forth, and from the
viewpoint of Mercury it's the Sun that's oscillating back and
forth. Beyond that, there is nothing else of any consequence
within that system. Mercury's orbit trajectory is determined
entirely from within that closed system.

Not a closed system. Jupiter perturbes the orbid of Mercury.

Bob Kolker