(direction coordinate along celestial equator)
Right ascension is the distance to an hour circle
as an angle measured along
the celestial equator eastward from the vernal equinox.
It and declination together specify a direction,
i.e., a point in the celestial sphere.
Declination and right ascension are analogous to
latitude and longitude, respectively.
Right ascension (but not declination)
is commonly cited in angular hours,
a unit equal to 15 degrees, i.e., the
angular distance the Earth rotates in an hour.
The hours are subdivided into minutes and seconds that
are 1/60 and 1/3600 of an angular hour.
(A degree is similarly divided into the smaller arcminutes and arcseconds,
i.e., an arcsecond is 1/15 of an angular second.)
Right ascension is also sometimes cited in degrees.
The hours are counted from a line from the Sun
through the Earth's position at the time of the
vernal equinox (March equinox), counting to a higher
number of hours as you go eastward.
For example, the constellation Orion has a right ascension
in the region of 5 hours and 30 minutes (it covers a portion of the
sky, so its area includes right ascensions from less than 5 hours
to more than 6 hours).
Hour angle is another type of measure of the placement
of an hour circle: there is more than one kind of hour angle,
but a common type counts hours from the observer, and
westward, i.e., the opposite direction around Earth as does
Referenced by pages:
AD Leonis (AD Leo)
Algol (Beta Per)
AU Microscopii (AU Mic)
Canis Major Dwarf Galaxy
Circinus Galaxy (ESO 97-G13)
Extended Groth Strip (EGS)
Epsilon Indi (ε Indi)
equatorial coordinate system
Gliese 436 b (GJ 436 b)
HD 189733 b
HD 209458 b
Hubble Deep Field (HDF)
Hubble Deep Field South (HDF-S)
Hubble Ultra-Deep Field (HUDF)
LHS 3844 b
Large Magellanic Cloud (LMC)
Crab Nebula (M1)
Triangulum Galaxy (M33)
Ohio Radio Survey (OSS)
Hulse-Taylor Binary (PSR B1913+16)
Rho Ophiuchi Cloud Complex
Sagittarius Dwarf Irregular Galaxy (SagDIG)
Sagittarius Dwarf Elliptical Galaxy (Sgr dE)
Small Magellanic Cloud (SMC)
Taurus Molecular Cloud 1 (TMC-1)
TOI 700 d
TW Hydrae (TW Hya)
Ursa Major II Dwarf