An arcsecond (second of arc), represented by the symbol ${\displaystyle ''}$,^[1] is a unit of angle used in mathematics and astronomy. An arcsecond is 1/60th of an arcminute (minute of arc),^[2] which in turn is 1/60th of a degree.^[3] Therefore, an arcsecond is equal to 1/3600th of a degree,^[2] meaning that there are 360 × 60 × 60 = 1,296,000 arcseconds in a full circle.

One milliarcsecond (mas) is a thousandth (1/1000th) of an arcsecond. So there are 1,296,000,000 milliarcseconds in a full circle. The red supergiant stars Antares, Betelgeuse,^[4] Mu Cephei, VV Cephei A, and VY Canis Majoris all have angular diameters (apparent sizes in the sky) of more than 10 milliarcseconds, when seen from Earth.

• Radian

1. ↑ "List of Geometry and Trigonometry Symbols". Math Vault. 2020-04-17. Retrieved 2020-08-31.
2. ↑ ^{2.0 2.1} Weisstein, Eric W. "Arc Second". mathworld.wolfram.com. Retrieved 2020-08-31.
3. ↑ Weisstein, Eric W. "Arc Minute". mathworld.wolfram.com. Retrieved 2020-08-31.
4. ↑ "Archived copy" (PDF). Archived from the original (PDF) on 2011-07-15. Retrieved 2023-09-06.{{cite web}}: CS1 maint: archived copy as title (link)

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