Gigameter

Gigameter (symbol Gm) is a unit of length in the metric system equal to 1,000,000,000 meters (10^9 m). It is formed from the SI prefix giga- and the base unit meter. The gigameter is used for expressing very large distances, notably within the Solar System, where distances that are impractical in meters or kilometers are more conveniently stated in gigameters.

Conversions and relation to other units: 1 Gm equals 1,000,000 kilometers (since 1 Gm = 10^9 m and 1 km = 10^3 m). It also equals 1,000 megameters (Mm). In astronomical terms, 1 AU is about 149.6 Gm, and the Earth–Moon distance is about 0.38 Gm.

Typical usage: While the astronomical unit (AU) remains the standard for expressing planetary distances in solar-system studies, the gigameter is a convenient SI-based scale for large but not interstellar distances, and it is sometimes used in space missions and navigation calculations.

History and scope: The gigameter is part of the SI prefix system and has been in use since the adoption of the metric system. It complements other length units such as the kilometer and the megameter.

See also: kilometre, megameter, astronomical unit, light-year.