Arcsecond

An angular second or arcsecond or second (from Latin pars minuta secunda 'second diminished part') is a unit of measure of angle and means the 3600th part of a degree. It is just about equal to the angle at which a five millimetre wide object appears from a distance of one kilometre. The symbol used is the second sign ″ or arcsec. The arcsec symbol is also used for the arcsec.

Thus, one angular second is equal to {\displaystyle {\tfrac {\;1^{\circ }}{3600}}=0{,}0002{\overline {7}}{}^{\circ }}

60 angular seconds correspond to one angular minute, 60 angular minutes correspond to one degree. In astronomy and earth measurement, the arcsecond is commonly used with further subdivisions that follow the decimal system: A milliarcsecond (mas) is one thousandth of an arcsecond (0.001″), a microarcsecond (µas) is one millionth of an arcsecond.

In the past, a further subdivision of the second into 60 tertians was common; for some procedures in navigation, this division is still used today.

Although the angular second is not part of the International System of Units (SI), it is permitted for use with the SI. This makes it a legal unit of measurement.

Conversion

{\displaystyle {\begin{aligned}{\text{Winkel (in Grad)}}&={\text{Grad}}+{\frac {\text{Winkelminuten}}{60}}+{\frac {\text{Winkelsekunden}}{3600}}\\&={\text{Grad}}+{\frac {{\text{Winkelminuten}}+{\frac {\text{Winkelsekunden}}{60}}}{60}}\end{aligned}}}

The conversion to radians is done accordingly, see Conversion between radians and degrees.

Symbol

The symbol for angular seconds is arcsec or the seconds sign. The latter consists of two straight, sloping strokes: 1″ = 1 angular second and thus corresponds to the inch sign. The typographically correct character in Unicode has code U+2033. Alternatively, two vertical bars (") are also used.


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