Gravitational torque from the Sun and Moon causes Earth's axial precession
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Peer-reviewed scientific literature and reference materials confirm that gravitational forces and torques exerted by the Sun and the Moon on Earth's equatorial bulge drive its axial precession and rotational variations.
Among the variations in the rotation of the Earth, the nutation is the most suitable for studying the Earth's internal structure. The nutation is mainly driven by the gravitational torque of the Moon, the Sun and the planets acting on its equatorial bulge. The Earth response to this external forcing is influenced by its internal structure. Because the gravitational forcing is known to a very good accuracy, the high precision nutation observations, using the very long baseline interferometry (VLBI) technique, allow to estimate Earth interior parameters. The nutational response of the nonrigid Earth to the gravitational forcing has previously been modeled by a semianalytic model which depends on parameters, related to the Earth interior, that are adjusted on the nutation observations. Those parameters are the dynamical ellipticities of the whole Earth and fluid core, compliances describing the deformability of the whole Earth and fluid core, and coupling constants related to the torques generated by the differential rotation of the mantle, fluid core and solid inner core. Most of the nutation models are frequency domain models so that, in previous studies, the time series of observations are processed before the fit in order to get data in the frequency domain. Because the parameters are fit only on the twenty dominant terms in the frequency domain, this fit leads to a loss of information. In this paper, we present a new fit procedure of the nutation model to the observations,
the case of the earth it is inferred from the independent phenomenon of luni-solar precession that (C − A)/A = .00313. Hence if the earth’s axis of rotation
fluences of the Sun and Moon that cause Earth to bulge at the equator, affecting its rotation. The trend in the direction of this wobble relative to the fixed positions of stars is known as axial precession . The cycle of axial precession spans about 25,771.5 years.
Axial precession makes seasonal contrasts more extreme in one hemisphere and less extreme in the other. Currently perihelion occurs during winter in the Northern Hemisphere and in summer in the Southern Hemisphere. This makes Southern Hemisphere summers hotter and moderates Northern Hemisphere seasonal variations. But in about 13,000 years, axial precession will cause these conditions to flip, with the Northern Hemisphere seeing more extremes in solar radiation and the Southern Hemisphere experiencing more moderate seasonal variations.
Precession does affect seasonal timing relative to Earth's closest/farthest points around the Sun. However, the modern calendar system ties itself to the seasons, and so, for example, the Northern Hemisphere winter will never occur in July. Today Earth’s North Stars are Polaris and Polaris Australis, but a couple of thousand years ago, they were Kochab and Pherkad.
There’s also apsidal precession . Not only does Earth wobble on its rotational axis, but Earth’s entire orbital ellipse – that is, the oval-shaped path Earth follows in its orbit around the Sun — also wobbles irregularly, primarily due to its interactions with Jupiter and Saturn. The cycle of apsidal precession spans about 112,000 years. Apsidal precession changes the orientation of Earth’s orbit relative to the ecliptic plane.
The combined effects of axial and apsidal precession result in an overall precession cycle spanning about 23,000 years on average.
A Climate Time Machine
The small changes set in motion by Milankovitch cycles operate separately and together to influence Earth’s climate over very long timespans, leading to larger changes in our climate over tens of thousands to hundreds of thousands of yea
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