presesjon

Presesjon is a phenomenon observed in rotating bodies, most notably in celestial mechanics. It refers to the slow, conical precession of the axis of rotation of a rotating body. Imagine a spinning top that is not perfectly upright; its axis of rotation slowly traces out a cone in space. This is the visual representation of presesjon.

In the context of Earth, the most familiar example, the axis of rotation slowly wobbles. This causes the direction of "true north" to shift over thousands of years. Currently, Polaris is the North Star, but due to presesjon, this will change in the distant future. The Earth's presesjon is primarily caused by the gravitational pull of the Moon and the Sun on Earth's equatorial bulge. This gravitational torque acts to try and pull Earth's axis into alignment with the plane of its orbit, but because Earth is spinning, it results in a precession rather than an immediate alignment.

The period of Earth's axial presesjon is approximately 26,000 years. This cycle has significant implications for astronomical observations and the Earth's climate over long timescales, influencing the timing of seasons relative to Earth's orbital position. The concept of presesjon is also relevant in physics and engineering for understanding the behavior of gyroscopes and other rotating systems.