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Symbol | Definition |
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≡ | exactly equal |
≈ | approximately equal to |
= | equal to |
digits | indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …) |
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.
A metric mile is a distance which approximates one statute mile (1609.344 m) at a round figure of metres (the SI or metric unit of length). The term is most commonly used in track running and swimming.
In track running, the 1500 m race became the standard middle distance race in Europe in the late 19th century, and has been the standard distance in the Olympic Games since 1896. The distance of the race is sometimes referred to as a metric mile.