My thanks to Lawrence Wilson, who has taken the time and trouble to continue investigating the controversy around the question of the focus of Earth’s orbit. This has an important bearing on the climate debate, as quite large swings in TSI will occur if the Earth orbits the solar system barycentre (SSB) rather than the Sun-Earth barycentre. Surprisingly, expert opinion seems to be that the Earth doesn’t orbit the Sun, but the SSB. I’m awaiting a reference to Newton’s calculations. All I’ve ever seen is a small illustration showing an ellipse around the sun, not an epitrochoid. This leaves me uncertain that Newton ever did detailed calculations resolving this issue.
Solar Inertial Motion – Earth/Sun Displacement
Lawrence Wilson – 19 Feb 2013
The phenomenon of SIM was defined mathematically by Isaac Newton,
his conclusion being that all planets followed a primary orbit around the SSB (their primary orbital foci) rather than the CofM of the Sun, indeed the Sun itself also proceeding on a seemingly ‘haphazard’ orbital dance around the SSB.
[Editor's note] Newton states that: “The focus of the orbit of the Earth [is] in the common centre of gravity of Venus, Mercury and the Sun.” – Mathematical Principles of Natural Philosophy Vol III pp28
In more technical terms its path is described as an epitrochoid, a path which is near repetitive each 178 years. Scientists subsequent to Newton who have studied the phenomenon and its potential implications, such as Jose, Landscheit, Fairbridge, Charvatova and numbers of others too, have independently validated Newton’s analysis.
Richard Mackey in his essay on the related work of Rhodes Fairbridge describes it in this way:-
The general form of the sun’s barycentric orbit is an epitrochoid, a big circle continuous with a little ring nestling asymmetrically inside it. At one phase, the orbit is nearly circular, almost two solar diameters in diameter. At another phase, the Sun is impelled on a backward, or retrograde, journey in which it undergoes a tight loop-the-loop, crossing over its own path in a loop that is less than one solar radius. The epitrochoid’s asymmetric ring arises from the sun undergoing the retrograde loop-the-loop.