jordaksen

Jordaksen is the imaginary line through the center of the Earth around which the planet rotates. It intersects the surface at the geographic North and South Poles and defines the direction of rotation. The axis is tilted relative to the plane of the Earth's orbit around the Sun by about 23.4 degrees, a tilt known as the obliquity.

This tilt causes the seasonal variation in solar radiation, as hemispheres are alternately tilted toward or away from the Sun during the year. The axis, however, is not fixed in space. It slowly traces a conical motion called precession, completing a full cycle roughly every 26,000 years, which makes the positions of the celestial poles drift relative to the stars. In addition, short-term wobbling called nutation introduces small oscillations in the axis over shorter timescales. The obliquity itself varies over tens of thousands of years, between about 22 and 24.5 degrees, on a cycle of roughly 41,000 years.

The jordaksen underpins geographic coordinates, day length, and seasonal patterns, and it links to the apparent motion of the sky. Today the North Celestial Pole lies near the star Polaris, but its position will change due to precession. In climate science, variations in obliquity and precession are components of the Milankovitch cycles, influencing long-term climate trends.