Precessionary

Precessionary refers to a phenomenon involving a slow, conical wobble of an astronomical body's rotational axis. This effect is most famously observed in the Earth's axial precession, also known as the precession of the equinoxes. The Earth's axis of rotation is not fixed in space; instead, it traces out a cone over a period of approximately 26,000 years. This means that the direction in space towards which the North Pole points gradually changes.

This slow change in orientation is caused by the gravitational pull of the Sun and Moon on the Earth's equatorial bulge. The Earth is not a perfect sphere, and its rotation creates a bulge around its equator. The gravitational forces of the Sun and Moon exert a torque on this bulge, causing the Earth's axis to precess, much like a spinning top wobbles when its axis is tilted.

The consequences of this precession are significant. For instance, it causes the celestial pole to shift over millennia. Currently, Polaris is the North Star, but in about 12,000 years, Vega will be the North Star. Precession also affects the timing of the seasons in relation to the Earth's position in its orbit, which is why it is called the precession of the equinoxes. This astronomical phenomenon is a fundamental aspect of understanding celestial mechanics and long-term astronomical cycles.