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A metric foot is a nickname for a preferred number length of 3 basic modules (3 M), or 30 centimetres (11.811 in). The 30 cm metric ruler was a similar length to the traditional imperial one-foot ruler. A metric foot is 4.8 millimetres (0.189 in) shorter than an imperial foot.
The light-year is a unit of length used to express astronomical distances. It is about 9.5 quadrillion metres or 5.9 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time.