aksehelling

Aksehelling, or axial tilt, is the angle between an object's rotation axis and the perpendicular to its orbital plane (the normal to the plane of orbit). In astronomy the term describes how much the axis of a planet, moon, or dwarf planet is tilted relative to its orbital plane around its primary. The tilt is a distinct property from precession, and while it can be altered over long timescales by gravitational interactions, it remains relatively fixed on human timescales.

On terrestrial planets the axial tilt has a major influence on climate and seasons, because it determines the distribution of sunlight between hemispheres during the year. Earth’s tilt is about 23.4 degrees; Mars about 25 degrees; Uranus about 98 degrees (essentially lying on its side). Mercury has a very small tilt, around 0.03 degrees. The tilt contributes to Milankovitch cycles, which include gradual changes in obliquity on timescales of tens of thousands of years and affect long-term climate patterns.

Measurement and estimation of aksehelling rely on astrometric observations, spacecraft orientation data, and analyses of a body’s rotation and orbital geometry. Knowledge of axial tilt is used in models of planetary atmospheres and climates, as well as in mission planning and navigation where precise orientation matters.

Etymology: the Norwegian term combines akse (axis) and helling (tilting). In English, the standard term is axial tilt or obliquity.