Question

What is the precession cycle? What causes it?

Answer 1

Hint: Because of Hipparchus' discovery, the term "precession" no longer means "step forward," but rather refers to any rotation of a spin axis around a cone, such as the precession of a gyroscope in an airplane's instrument or the precession of a rotating satellite in space.

Complete answer:
A transition in the direction of a moving body's rotational axis is known as precession. The period for such transition is known as the Precession cycle. It can be defined as a shift in the first Euler angle in an acceptable reference frame, while the third Euler angle describes the rotation itself. To put it another way, if a body's axis of rotation rotates around a second axis, the body is assumed to be precessing around the second axis. There are two forms of precession in physics: torque-free and torque-induced precession.

Precession cycle is the term for a cyclic wobbling in the direction of the Earth's axis of rotation with a period of \[25,772\] years. After the much more apparent regular rotation and annual revolution, precession was the third motion of the Earth to be discovered. The precession era is about \[{\text{26000}}\] years. This is the Precession Cycle. Like a revolving top, the Earth's axis rotates (precesses). As a result, the North Celestial Pole would not always point in the same direction.

The gravitational force of the Sun and Moon on the Earth causes precession. The planets still have an effect, albeit to a much lesser degree. The precession is caused by the Earth's equatorial bulge, which is caused by the centrifugal force of rotation. The Earth's rotation transforms it from a smooth sphere to a slightly flattened sphere with a thicker equator. The "nudge" caused by the Moon and Sun's attraction on the bulge causes the Earth to precess.

Note: During each \[{\text{26000}}\]-year period (precession cycle), the axis points in the sky in the direction of a large circle whose circumference covers an angle of about \[{23.5^0}\]. The pole star to which the axis now points (within around one degree) used to be further away from the pole than it is now, and it will be again in a few thousand years (for your information, the closest approach was in \[2017\]).