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Astronomy/rotation of the Sun


Obviously, the  rotation of the Sun around the Galactic Center will generate a centrifugal force which is directly proportional to its distance from the galactic center
Contrary to the force of gravity between them which is inversely proportional to the square of the distance, according to Newton's law of universal gravitation
As Kepler believed that the Sun is the center of the Galaxy, this means that he was not aware of  the centrifugal force and its impact on planets in the way of rotation  about the Sun, knowing that he bases his laws on the legend of heliocentric universe. Have we right to ask:
1- Could we say that, although Kepler was unaware of Sun's rotation around the Galactic Center  this does not affect the validity of his laws? And what ever was the Sun in the galactic center or orbiting it, Kepler's laws must stay like it is?
2-What is the probability that the centrifuge may has any effect on planetary orbits in terms of shape and way of acceleration and deceleration? Especially if Kepler did not know the cause of the elliptical shape of the orbits and he couldn't explain why the planets accelerate in approaching the Sun and decelerate in getting far from it.
3-Is there a possibility that Kepler while watching the movement of the planets by his eyes, have failed in the deception of sight, seeing the planet is accelerating but is really slowing, and when it is accelerating, in fact, sees it slowing, .Especially he did not know that everything around him, the planets, the Earth and the Sun was in movement, and was not including any fixed body that he can take as a reference, making his ability to distinguish between all these mobiles extremely difficult?
Thank you
Dr Barzaq

Points addressed:

1) There is no such force as "centrifugal force". The correct force is centripetal - a center directed force that is equated to the force of gravitational  attraction (F = GMm/r^2) "Centrifugal" force is a fictional force often created by incompetent authors to try to account for circular motion but which is not needed at all, and only confuses the situation.

2) Whatever centripetal force is attendant on the galactic rotation would have no bearing on the formulation of Kepler's laws. Hence, it would not affect the validity of his laws. (We are talking about two distinct inertial reference frames)

3) By the same token, this galactic centripetal force would have no bearing on on the planetary orbits, their orbital parameters, shape of orbits etc.

4) Kepler did not have to know 'everything' regarding the elliptical orbits but surely would have enough physics background to realize the planets would speed up at the nearest point to the Sun (perihelion) and slow at the furthest point (aphelion).

All of this means that Kepler's laws remain valid and there is no practical way of rationalizing one's way out of accepting them.


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Philip Stahl


I have more than forty years of experience in Astronomy, specifically solar and space physics. My specialties include the physics of solar flares, sunspots, including their effects on Earth and statistics pertaining to sunspot morphology and flare geo-effectiveness.


Astronomy: Worked at university observatory in college, doing astrographic measurements. Developed first ever astronomy curriculum for secondary schools in Caribbean. Gave workshops in astrophysics and astronomical measurements at Harry Bayley Observatory, Barbados. M.Phil. degree in Physics/Solar Physics and more than twenty years as researcher with discovery of SID flares. Developed of first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Develop first ever loop solar flare model using double layers and incorporating cavity resonators.

American Astronomical Society (Solar Physics and Dynamical Astronomy divisions), American Mathematical Society, American Geophysical Union.

Solar Physics (journal), The Journal of the Royal Astronomical Society of Canada, The Proceedings of the Meudon Solar Flare Workshop (1986), The Proceedings of the Caribbean Physics Conference (1985). Books: 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level'. 'Astronomy and Astrophysics: Notes, Problems and Solutions'.

B.A. Astronomy, M. Phil. Physics

Awards and Honors
American Astronomical Society Studentship Award (1984), Barbados Government Award for Solar Research (1980), Barbados Astronomical Society Award for Service as Journal Editor (1977-91)

Past/Present Clients
Caribbean Examinations Council, Barbados Astronomical Society, Trinidad & Tobago Astronomical Society.

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