Arcsecond

A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7.7×10-7 of a circle. It is the angular diameter of an object of 1 unit diameter at a distance of 360×60×60/(2π) ≈ 206,265 units, such as (approximately) 1 cm at 2.1 km, or 1 astronomical unit at 1 parsec, which is the definition the parsec.

Related Topics:
Angular - Arcminute - Degree of arc - Circle - Angular diameter - Distance - Astronomical unit - Parsec

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Correspondingly, 1 radian ≈ 206,265 arcseconds.

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The symbol for marking the arcsecond is the double prime (″) (U+2033, ″). One arcsecond would be 1″ (or 1"). The double prime symbol is also used to denote the inch: this can, in certain contexts, cause confusion.

Related Topics:
Double prime - Inch

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It can be abbreviated as arcsec, but should then not be confused with the inverse trigonometric function arc secant, which has the same abbreviation.

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