megameters

A megameter (symbol Mm) is a unit of length in the metric system equal to 1,000,000 meters. It is a derived unit formed from the SI prefix mega- (10^6) and the meter. Because 1 Mm is 1,000 kilometers, the megameter is mainly used for measuring very large distances where kilometers would produce unwieldy numbers, but meters are still preferred over kilometers in certain scientific calculations.

In practice, megameters appear in astronomy and geodesy. For example, the mean distance from the Earth to the Moon is about 384.4 Mm, and distances within the solar system are commonly reported in tens to hundreds of thousands of megameters. One astronomical unit (AU) equals about 149,600 Mm, meaning that 1 AU ≈ 149,600 Mm.

Other examples: Earth's diameter is about 12.742 Mm, while solar system objects span from fractions of a megameter to tens of millions of megameters. Nevertheless, many scientists prefer kilometers or astronomical units for readability, and light-years or parsecs for interstellar scales.

See also: meter, kilometer, astronomical unit, light-year, parsec. The megameter is part of SI derived units and is seldom used in everyday measurements.