J2000.0 equinox
(equinox as of the J2000.0 epoch used as a positional reference)
J2000.0 equinox is a standard direction (or equivalently,
an adopted specific point on the celestial sphere)
that is currently used as a reference in astronomy,
being the position of the vernal equinox (March equinox)
as of epoch J2000.0 (the equinoxes undergo a slow, constant shift,
i.e., the precession of the equinoxes).
The current standard equatorial coordinate system
(i.e., with coordinates right ascension and declination)
are defined such that coordinates J000000+000000 represent
this standard direction.
Before J20000.0 equinox was adopted, earlier such standard equinoxes
were used (similarly based upon earlier standard epochs),
each equinox adopted for reports/catalogs
occurring near in time to the standard epoch it was based upon.
For example, prior to standardization
of the J2000.0 equinox, the B1950.0 equinox (analogously based
on epoch B1950.0) was used as the standard.
The J2000.0 vernal equinox in the B1950.0 coordinates
is approximately B235726.23391-001641.2260,
a shift of roughly 40 arcminutes.
Conversely, the B1950.0 vernal equinox in J2000.0 coordinates
is approximately J000233.76588+001642.2244.
(astronomy,designation)
Further reading:
https://en.wikipedia.org/wiki/Equinox_(celestial_coordinates)#J2000.0
https://oneau.wordpress.com/2011/10/27/equinox-epoch/
Coordinates: | J2000.0 equinox J000000+000000 |
|
Referenced by pages:
celestial reference frame
epoch B1950.0
epoch J2000.0
equinox
J designator
precession of the equinoxes
Index