What is "gigametre"

n. (context chiefly International British Canada English) A distance of 1,000,000 kilometres.

The gigametre ( official spelling used by the International Bureau of Weights and Measures; SI symbol: Gm) or gigameter ( American spelling) is a unit of length in the metric system, equal to one billion metres, the SI base unit of length, hence to or approximately .

Gigametres (from the Greek words gigas = giant and metro = count/measure) are rarely seen in practical use. They are too big for any terrestrial lengths, and gigametre distances in astronomy (e.g. a planet's distance from its star) are usually given in astronomical units (AU) or in (millions of) kilometres.

• Earth's average distance from the Sun is 149.6 Gm or 1 AU.
• Jupiter's average distance from the Sun is 778.5 Gm or 5.2 AU.
• Osiris' average distance from the parent star HD 209458 is 6.7 Gm or 0.045 AU.
• PSR J1719-1438 b's average distance from the pulsar PSR J1719-1438 is 0.666 Gm, which is the smallest orbit of any known exoplanets.
• The mean diameter of the Sun is 1.393 Gm.
• The mean diameter of red supergiant star Betelgeuse is .