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I read this post on another physics forum. I thought Keplers laws were accurate for our earth/sun system?

"Keplers law is so easily disproven

Keplers Law states that the planets move in elliptical orbits with the sun at one focus of the ellipse so that a line connecting the sun and a planet will sweep out equal areas in equal times.

An ellipse is a central conic symmetric about a central point so that the major axis passing through the focus bisects the ellipse making the areas of both sides of the bisected ellipse equal.

The perihelion and aphelion are the closest and furthest points from the sun the focus that the Earths orbit intersects the major axis.

By applying Kepler's Law to the Earth's orbit, these points are placed in early January and July. However, the time it takes for the Earth to move between these astronomical points, January to July is 72 hours less than the time it takes to move from July to January, sweeping out equal areas in unequal times. Thus, applying Kepler's Law to determine the perihelion and aphelion of the Earth's orbit disproves Kepler's Law!

The fact that it takes longer for the Earth to move between the summer (June) and winter (December) solstices than it does to move between the winter and summer solstices shows that the sun is moving toward the winter solstice.

Bottom line

Newton based his proof of mass/gravity on historical forces producing Kepler's Law we may have to rethink why objects fall."