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The megametre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: Mm) or megameter (American spelling) is a unit of length in the metric system, equal to one million metres, the SI base unit of length, hence to 1,000 km or approximately 621.37 miles. Megametres (from the Greek words ''megas'' = big and ''metro'' = count/measure) are rarely seen in practical use, e.g. "5000 km" is much more common than "5 Mm". Unless dealing with astronomy, distances on Earth can't be more than 40,075 km (Equator length), although megametres may be used to measure the extensions of road systems and air travel distances, among other things rather than distances. The symbol (Mm) can also be confused with millimetres (mm) and care should be taken to use the correct capitalisation when using such symbols. Megametres are also occasionally found in science fiction. *The Earth's polar circumference is 39.94 Mm. (It was exactly 40 Mm from 1791 to 1875, but the definition of the metre was changed; see metre). *The distance from Amsterdam to Marseille is 1.01 Mm. *The distance from New York City to Chicago is 1.14 Mm. *The Earth's equatorial diameter is 12.76 Mm. *Quebec province's total area is 1.542 Mm2. *The mean distance from the Earth to the Moon is 384.4 Mm. *Jupiter's equatorial diameter is 143 Mm. *The speed of light is approximately 299.792 Mm/s. ==See also== *1 E+6 m *SI *SI prefix *Metric system *Orders of magnitude (length) *Conversion of units, for comparison with other units of length *Light year *Parsec 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Megametre」の詳細全文を読む スポンサード リンク
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