Bilunir

Bilunir is a neologism used in astronomy and science fiction to denote a celestial body that possesses two natural satellites or moons. The term is formed from bi-, meaning two, and luna, meaning moon, reflecting its intended meaning of “two moons.” In formal astronomy, bilunir is not an official category and is not part of the International Astronomical Union nomenclature; objects with two moons are instead described by their satellites and orbital properties.

Usage of bilunir is largely informal. It appears mainly in speculative contexts or introductory explanations of moon systems, rather than in peer-reviewed research. The term may be used to discuss the orbital dynamics of a two-moon system around a planet, including resonant interactions, orbital stability, and tidal evolution. In science fiction, bilunir is sometimes employed as a shorthand for a world with two prominent moons or as a plot device involving eclipses and tidal forces.

Because bilunir is informal, its precise meaning can vary by author. Some definitions require exactly two confirmed moons around the host planet, while others use bilunir more loosely to describe systems with two major satellites plus minor irregulars. The concept highlights the interest in how dual-moon configurations affect a planet’s geology, climate, and observational characteristics.

See also: Exomoon, Moon, Binary planet, Satellite, Orbital resonance.