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# arcsecond

( or as or sec or s)
a unit of angular measure, also called the second of arc, equal to 1/60 arcminute. One arcsecond is a very small angle indeed: there are 1 296 000 seconds in a circle. The SI defines s as the symbol for the time unit and recommends ″ as the symbol for the arcsecond. The symbol as has become common in astronomy, where very small angles are stated in milliarcseconds (mas).

Dictionary of units of measurement. 2015.

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