Astrophysics (index)about

arcsecond

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

An arcsecond (arcsec or just 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 (unit of angle corresponding to 1/360 of a full circle) is divided into 60 arcminutes (arcmin or just 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 and micro-arcsecond are 1/1,000 and 1/1,000,000 of this value.

Right ascension is commonly measured in hours (which might logically be called 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), which are not the same angular size as the arcsecond and arcminute associated with degrees. (As far as I can tell, the terms arcsecond and arcminute are unambiguous, but one must be careful with the terms second and minute.)

Astronomers sometimes avoid hours, minutes and/or seconds: radians may be used, or hours for right ascension may be avoided in favor of degrees, or degrees (and/or hours) may be expressed in decimal fashion when specifying more angular precision.


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

Referenced by:
Anglo-Australian Telescope (AAT)
Atacama Cosmology Telescope (ACT)
angular resolution
Australia Telescope Compact Array (ATCA)
C-BASS
Canada-France-Hawaii Telescope (CFHT)
CHARA
CRATES
Extended Groth Strip (EGS)
Einstein Telescope
EMPIRE Survey
equatorial coordinate system
fast radio burst (FRB)
Holmberg radius
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
gravitational microlensing
Ohio Radio Survey
Ooty Radio Telescope (ORT)
Pan-STARRS
parallax
parsec (pc)
PAWS
Plateau de Bure Interferometer (PdBI)
pointing error (PE)
plate scale
proper motion
Rho Ophiuchi Cloud Complex
SCUBA
seeing
solid angle (Ω)
spacetime diagram
SPHEREx
2dF-SDSS LRG and QSO survey (2SLAQ)
Uppsala General Catalogue (UGC)
Very Large Array (VLA)

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