Quote:
Originally Posted by bojan
OK...
Could you then explain to me (and others) exactly why and how spiral motion causes precession, maybe I am misunderstanding something.
I included link from wikipedia above to help you point out for us what you think is my problem. |
Sorry bojan .
for the delay I’ve been a little busy of late.
I did try to visit your wiki reference by copying and pasting the address but was unsuccessful
Yes of course, my explanation.
The precession of the equinoxes is the key to understanding the spiral mode of Earth’s orbit about the Sun. the Sun’s gravitation effect on the Earth is paramount as it is with whole solar system I think you will agree. It has a strong influence on both of Earth’s forms of motion. It’s rotation on its axis and it’s revolution about the Sun.
As a preliminary it will be useful to quote Isaac Newton on his observations and study of planetary motion; from the ‘Principia’ (1687) aided with the impressions that he received from Dr, Robert Hooke during their earlier correspondence during 1679 where Hooke asked him to review his work – ‘The Attempt to Prove the Motion of the Earth from Observations’.
Hooke’s observations which obviously influenced Newton was the movement of the spheres to the centre etc. I quote a short extract:
“First, That all Coelestial Bodies whatsoever, have an attraction or gravitating power towards their own Centers, whereby they attract not only their own parts, and keep them from flying from them, as we may observe the Earth to do, but that they do also attract all the other Coelestial Bodies that are within the sphere of their activity; and consequently that not only the Sun and Moon have an influence upon the body and motion of the Earth, and the Earth upon them, but that also , , , and by their attractive powers, have a considerable influence upon its motion as in the same manner the corresponding attractive power of the Earth hath a considerable influence upon every one of their motions also.
The second supposition is this, That all bodies whatsoever that are put into a direct and simple motion, will so continue to move forward in a streight line, till they are by some other effectual powers deflected and bent into a Motion, describing a Circle, Ellipsis, or some other more compounded Curve Line.” End of quote
In the Principia it is evident that Newton had absorbed much from their discussions , where Hooke had clearly advanced the new notion that planetary motion was an ellipsis or a curved line. Towards the end of their correspondence, as they were considering the movement of the spheres to the centre, Hooke produced a sketch. A beautiful elliptical spiral.
There is much more to be told that followed but Its getting late for me, so tomorrow we will look at what Newton said in his ‘Principia’ about the movement to a centre , 7 years after Hooke’s death; plenty of time to contemplate on the risk of declaring an orbit as a spiral motion.
Have nice day , Alan D.