Ikkesfæriske

Ikkesfæriske is an adjective used in geometry and astronomy to describe objects that are not perfectly spherical. The term derives from Danish or Norwegian ikke meaning not and sfæriske meaning spherical, itself from Latin sphaericus. In practice, ikkesfæriske bodies span a range from slightly oblate or prolate ellipsoids to highly irregular shapes that deviate markedly from a sphere.

Quantifying non-sphericity relies on several measures. Common parameters include oblateness or flattening f, defined roughly as f = (a − c)/a for an ellipsoid with equatorial radius a and polar radius c, and the axial ratios a ≥ b ≥ c. A perfect sphere has f = 0 and all axes equal; real bodies have f > 0 and unequal axes. The dimensionless sphericity Φ, defined as the ratio of the surface area of a sphere with the same volume to the object's surface area, also describes deviation from sphericity when applicable.

Causes of ikkesfæriske shapes include rotation, which creates an equatorial bulge, and tidal forces in close binary systems or during close planetary encounters. Internal heterogeneity, past collisions, and accretion history can further distort shapes. In planetary science and astronomy, non-sphericity affects gravity fields, rotation rates, geophysical processes, and orbital dynamics, influencing mission design and surface exploration.

Measurement often relies on light-curve analysis, radar imaging, direct spacecraft mapping, and gravity measurements from tracking satellites. Notable examples include the Earth’s oblate shape, Jupiter’s modest oblateness, and the irregular forms of many asteroids and small bodies.

While 'ikkesfæriske' is primarily used in some Scandinavian contexts, in English texts the terms non-spherical, ellipsoidal, or irregular are typically employed to convey similar ideas.