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Exameter or examatre is a unit of length equal to 1018meters. This unit is a combination of the metric prefix exa (E) and the SI unit of length meter (m) and its abbreviated as "Em". Plural name is exameters.
The light-day is a unit of length useful in astronomy, telecommunications and relativistic physics. It is defined as the distance that light travels in free space in oneday, and is equal to exactly 2.59020683712×1013 metres.