About Jayendra Upadhye Expertise 1 - General questions on most astronomy topics such as:-
Solar system, Cosmology, Black holes, Quasars, Dark matter etc.
2 - General questions about the geologies of planets.
3 - General questions about Orbits and laws governing them.
4 - General questions about rockets / spaceships
5 - General questions about stellar interiors and supernovas.
Experience I was an askme.com expert rated no#1 for quite some time - and was top ten there by the time it closed - in Astronomy and general science categories.
Education/Credentials Bachelor of Engg. (Electrical engg), Maharaja Sayajirao university of Baroda, Gujarat, India.
Awards and Honors None to write about except the askme rating if it is any worth!
Question IF THE EARTH HAD A ZERO AXIAL TILT I THINK THAT THE PRECESSION OF THE
EQUINOX WOULD BE MUCH LESS THAN CURRENT, HOW COULD YOU
CALCULATE THE PRECESSION. CURRENTLY IT TAKES APPROX 26800 YEARS
TO COMPLETE ONE FULL CYCLE.
THANK YOU
Answer Hi wayne,
A very interesting question.
The period is 25800 not 26800. precession was known to the ancient hindu astronomers too as enough evidence of the same is found in their old astronomical data.
The REASOM for the gyration (precession) is the difference in axial orientation and the axis if oblateness which is always perpendicular to the ecliptic. This results in a "straightening force" on the tilted axis, verymuch like (but opposite in sense) to gravity trying to topple a tilted top and causing it to gyrate.
Here the sun+moon pull on the tidal bulges and try to make the axial tilt 0 degrees. (very very weakly) That creates the 25,800 year gyration.
Coming to your question, if the tilt were 0, there would be no precession, unless some residual one, due to misallignment of the earth's orbital plane with that of the moon.
[The lunar orbit is not coplanar with the earth, so it would still exert a pull on the rotating earth and cause it to gyrate!].
Though for me it is difficult to give you an estimate honestly, about what fraction of the gyration is due to the moon.
