### arcsecond

(arcsec, sec, second of arc, second)
(a 3600th of an angular degree)

An arcsecond (arcsec or second of arc, or in context, second or sec) is a unit of angle or arc, commonly used in astronomy for celestial sphere coordinates and distances across the sky. A degree (angular degree, unit of angle corresponding to 1/90 of a right angle) is divided into 60 arcminutes (arcmin, minute of arc, or in context, minute or min), which, in turn, is divided into 60 arcseconds, making an arcsecond 1/3600 of a degree or 1/1,296,000 of a full circle, or 2π/1,296,000 of a radian. A milli-arcsecond (or mas) and micro-arcsecond are 1/1,000 and 1/1,000,000 of this unit.

Right ascension is traditionally measured in hours (aka angular hours), 1/24 of a full circle, corresponding to 15 degrees. Fractions of an hour are also expressed as minutes (1/60 hour) and seconds (1/60 minute).

Astronomers sometimes avoid angular hours, minutes and/or seconds: radians (1/2π of a full circle, the length of the circle's radius) may be used, or right ascension may be cited in degrees. Also, degrees (and others of these units) are sometimes expressed in decimal fashion rather than using minutes or seconds.

Relations:

 unit degrees hours radians degree 1 1/15 π/180 arcminute 1/60 1/900 π/10800 arcsecond 1/3600 1/54000 π/648000 hour 15 1 π/12 minute 1/4 1/60 π/720 second 1/240 1/3600 π/43200 radian 180/π 12/π 1 full circle 360 24 2π

(unit)
http://en.wikipedia.org/wiki/Minute_and_second_of_arc
http://en.wikipedia.org/wiki/Degree_(angle)
http://en.wikipedia.org/wiki/Right_ascension

Referenced by pages:
Anglo-Australian Telescope (AAT)
aberration
ACBAR
Atacama Cosmology Telescope (ACT)
angular resolution
Archeops
ASCA
Australia Telescope Compact Array (ATCA)
ATHENA
Barnard's Star
C-BASS
celestial pole
CHARA
Circinus Galaxy (ESO 97-G13)
CONCERTO
CRATES
Extended Groth Strip (EGS)
Einstein Telescope
EMPIRE Survey
equatorial coordinate system
ESO 137-001
field of view (FOV)
high-resolution imaging
Hubble Ultra-Deep Field (HUDF)
interferometer
J designator
Kapteyn's Star
Lacaille 9352
Luyten Half-second Catalog (LHS)
Large Millimeter Telescope (LMT)
Luyten Two-Tenths Arcsecond Catalog (LTT)
Lynx
M64
Messier 74 (M74)
M82
M87
gravitational microlensing
NGC 1600
NGC 3314
Narrabri Stellar Intensity Interferometer (NSII)
nutation
Pan-STARRS
parallax
parsec (pc)
PAWS
Plateau de Bure Interferometer (PdBI)
pointing error (PE)
plate scale
proper motion (PM)
Rho Ophiuchi Cloud Complex
Sagittarius Dwarf Irregular Galaxy (SagDIG)
Sagittarius Dwarf Elliptical Galaxy (Sgr dE)
SCUBA
seeing
solid angle (Ω)
spacetime diagram
Spektr-R
SPHEREx
standard ruler
Teegarden's Star
2dF-SDSS LRG and QSO survey (2SLAQ)
Uppsala General Catalogue (UGC)
Uhuru
Very Large Array (VLA)
WISE 0855-0714 (W0855)

Index