quasicircular

Quasicircular is an adjective describing something that is nearly circular in shape or motion—close to a perfect circle but with small deviations. The term is used across disciplines to denote near-circularity without requiring exact circularity.

In orbital mechanics, a quasi-circular orbit is an orbital trajectory with very small eccentricity, typically e much less than 1. The radial distance varies little around a mean value, and the motion can be well approximated as circular for analytical or numerical purposes. Quasi-circular orbits arise naturally as binaries emit gravitational radiation or through tidal interactions, which damp eccentricity over time. Planets in the Solar System have orbits that are very nearly circular, and exoplanets are often described as quasi-circular when measurements are insufficient to rule out small eccentricities.

In mathematics and geometry, the term is related to quasicircles, curves that are images of a circle under a quasiconformal mapping of the plane. A boundary that is a quasicircle is used to describe quasi-circular domains, generalizing the disk by controlled distortion. In this sense, a quasi-circular figure is not exactly a circle but approximates one with bounded distortion.

See also: circle, ellipse, eccentricity, quasi-circle, quasiconformal mapping, quasicircle.