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.help ccsystems Mar00 Skywcs
.ih
NAME
ccsystems -- list and describe the supported sky coordinate systems
.ih
USAGE
help ccsystems
.ih
SKY COORDINATE SYSTEMS
The sky package supports the equatorial ("fk4", "fk4-noe", "fk5", "icrs"),
ecliptic, galactic, and supergalactic celestial coordinate systems. In most
cases and unless otherwise noted users can input their coordinates in
any one of these systems as long as they specify the coordinate system
correctly.
Considerable flexibility is permitted in how the coordinate systems are
specified, e.g. J2000.0, j2000.0, 2000.0, fk5, fk5 J2000, and fk5 2000.0
all specify the mean place post-IAU 1976 or FK5 system. Missing equinox and
epoch fields assume reasonable defaults. In most cases the
systems of most interest to users are "icrs", "j2000", and "b1950"
which stand for the ICRS J2000.0, FK5 J2000.0 and FK4 B1950.0 celestial
coordinate systems respectively. The full set of options are listed below:
.ls equinox [epoch]
The equatorial mean place post-IAU 1976 (FK5) system if equinox is a
Julian epoch, e.g. J2000.0 or 2000.0, or the equatorial mean place
pre-IAU 1976 system (FK4) if equinox is a Besselian epoch, e.g. B1950.0
or 1950.0. Julian equinoxes are prefixed by a J or j, Besselian equinoxes
by a B or b. Equinoxes without the J / j or B / b prefix are treated as
Besselian epochs if they are < 1984.0, Julian epochs if they are >= 1984.0.
Epoch is the epoch of the observation and may be a Julian
epoch, a Besselian epoch, or a Julian date. Julian epochs
are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to the epoch type of
equinox if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date. If undefined epoch defaults to equinox.
.le
.ls icrs [equinox] [epoch]
The International Celestial Reference System where equinox is
a Julian or Besselian epoch e.g. J2000.0 or B1980.0.
Equinoxes without the J / j or B / b prefix are treated as Julian epochs.
The default value of equinox is J2000.0.
Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date. If undefined epoch defaults to equinox.
.le
.ls fk5 [equinox] [epoch]
The equatorial mean place post-IAU 1976 (FK5) system where equinox is
a Julian or Besselian epoch e.g. J2000.0 or B1980.0.
Equinoxes without the J / j or B / b prefix are treated as Julian epochs.
The default value of equinox is J2000.0.
Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date. If undefined epoch defaults to equinox.
.le
.ls fk4 [equinox] [epoch]
The equatorial mean place pre-IAU 1976 (FK4) system where equinox is a
Besselian or Julian epoch e.g. B1950.0 or J2000.0,
and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the
observation.
Equinoxes without the J / j or B / b prefix are treated
as Besselian epochs. The default value of equinox is B1950.0. Epoch
is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date. If undefined epoch defaults to equinox.
.le
.ls noefk4 [equinox] [epoch]
The equatorial mean place pre-IAU 1976 (FK4) system but without the E-terms
where equinox is a Besselian or Julian epoch e.g. B1950.0 or J2000.0,
and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the
observation.
Equinoxes without the J / j or B / b prefix are treated
as Besselian epochs. The default value of equinox is B1950.0.
Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian day. If undefined epoch defaults to equinox.
.le
.ls apparent epoch
The equatorial geocentric apparent place post-IAU 1976 system where
epoch is the epoch of observation.
Epoch is a Besselian epoch, a Julian epoch or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian
epochs if the epoch value < 1984.0, Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date.
.le
.ls ecliptic epoch
The ecliptic coordinate system where epoch is the epoch of observation.
Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian epochs
if the epoch values < 1984.0, Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian day.
.le
.ls galactic [epoch]
The IAU 1958 galactic coordinate system.
Epoch is a Besselian epoch, a Julian epoch or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian
epochs if the epoch value < 1984.0, Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date. The default value of epoch is B1950.0.
.le
.ls supergalactic [epoch]
The deVaucouleurs supergalactic coordinate system.
Epoch is a Besselian epoch, a Julian epoch or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian
epochs if the epoch value < 1984.0, Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date. The default value of epoch is B1950.0.
.le
Fields enclosed in [] are optional with the defaults as described. The epoch
field for the "icrs" , "fk5", "galactic", and "supergalactic" coordinate
systems is only used if the input coordinates are in the equatorial fk4,
noefk4, fk5, or icrs systems and proper motions are used to transform from
coordinate system to another.
.ih
SEE ALSO
.endhelp
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