astro::coord(3)

NAME

Astro::Coord - Astronomical coordinate transformations

SYNOPSIS

use Astro::Coord;
($l, $b) = fk4gal($ra, $dec);
($az, $el) = eqazel($ha, $dec, $latitude);

DESCRIPTION

Astro::Coord contains an assorted set Perl routines for
coordinate conversions, such as hour angle to elevation
and J2000 to B1950.

AUTHOR

Chris Phillips phillips@jive.nl

FUNCTIONS pol2r

($x, $y, $z) = pol2r($polar1, $polar2);
Converts a position in polar coordinates into rectangular coor
dinates: $polar1, $polar2 The polar coordinates to convert (turns)
$x, $y, $z The rectangular coordinates
r2pol
($polar1, $polar2) = r2pol($x, $y, $z);
Converts a position in rectangular coordinates into polar coor
dinates: $x, $y, $y The rectangular coordinates to convert
$polar1, $polar2 The polar coordinates (turns);
Returns undef if too few or too many arguments are passed.
xy2azel: ($az, $el) = xy2azel($x, $y);
Converts a telescope position in X,Y coordinates into Az,El co
ordinates: $x, $y The X and Y coordinates (turns)
$az, $el The azimuth and elevation (turns)
azel2xy
($x, $y) = azel2xy($az, $el);
Converts a position in Az,El coordinates into X,Y coordinates: $az, $el The azimuth and elevation (turns)
$x, $y The X and Y coordinate (turns)
eqazel
($ha, $dec) = eqazel($az, $el, $latitude); ($az, $el) = eqazel($ha, $dec, $latitude);
Converts HA/Dec coordinates to Az/El and vice versa.: $ha, $dec Hour angle and declination of source (turns)
$az, $el Azimuth and elevation of source (turns)
$latitude Latitude of the observatory (turns)
Note:: The ha,dec and az,el conversion is symmetrical
fk4fk5
($JRA, $JDec) = fk4fk5($BRA, $BDec);: (@fk5) = fk4fk5(@fk4);
Converts an FK4 (B1950) position to the equivalent FK5 (J2000) position.: $BRA,$BDec fk4/B1950 position (turns)
$JRA,$Dec fk5/J2000 position (turns)
@fk4 fk4/B1950 position (as a 3-vector)
@fk5 fk5/J2000 position (as a 3-vector)
Note:: This code is based on similar routines from the Fortran SLALIB
package, so are quite accurate, but subject to a restrictive
license (see README).
fk4fk5r
@fk5 = fk4fk5r(@fk4);
Converts an FK4 (B1950) position to the equivalent FK5 (J2000)
position. Note: Convert equitoral positions to/from 3-vectors using pol2r
and r2pol.: @fk4 fk4 position (as a 3-vector, turns)
@fk5 fk5 position (as a 3-vector, turns)
Note:: Just a wrapper to fk4fk5 which now handler polar and rectangu; lar
arguments
fk5fk4
($JRA, $JDec) = fk4fk5($BRA, $BDec);: ($@fk5) = fk4fk5(@fk4);
Converts an FK5 (J2000) position to the equivalent FK4 (B1950)
position.: $JRA,$Dec fk5/J2000 position (turns)
$BRA,$BDec fk4/B1950 position (turns)
@fk5 fk5/J2000 position (as a 3-vector)
@fk4 fk4/B1950 position (as a 3-vector)
Note:: This code is based on similar routines from the Fortran SLALIB
package, so are quite accurate, but subject to a restrictive
license (see README).
fk4galr
@gal = fk4galr(@fk4)
Converts an FK4 position (B1950.0) to the IAU 1958 Galactic coordinate system Note: convert equitoral positions to/from 3-vectors using pol2r
and r2pol.: @fk4 fk4 position to convert (as a 3-vector, turns)
@gal Galactic position (as a 3-vector, turns)
Returns undef if too few or two many arguments are passed. Reference : Blaauw et al., 1960, MNRAS, 121, 123.
galfk4r: @fk4 = galfk4r(@gal)
Converts an IAU 1958 Galactic position to the FK4 coordinate
system (B1950) Notes: Convert equitoral positions to/from 3-vectors using pol2r
and r2pol.: @gal Galactic position (as a 3-vector, turns)
@fk4 fk4 position (as a 3-vector, turns)
Reference : Blaauw et al., 1960, MNRAS, 121, 123.
fk4gal: ($l, $b) = fk4gal($ra, $dec);
Converts an FK4 position (B1950) to the IAU 1958 Galactic coordinate system: ($ra, $dec) fk4 position to convert (turns)
($l, $b) Galactic position (turns)
Reference : Blaauw et al., 1960, MNRAS, 121, 123.
galfk4: ($ra, $dec) = galfk4($l, $b);
Converts an IAU 1958 Galactic coordinate system position to FK4 (B1950).: ($l, $b) Galactic position (turns)
($ra, $dec) fk4 position to convert (turns) Reference : Blaauw et al., 1960, MNRAS, 121, 123.
ephem_vars
($omega, $rma, $mlanom, $F, $D, $eps0) = ephem_vars($jd)
Given the Julian day ($jd) this routine calculates the
ephemeris values required by the prcmat and nutate routines
The returned values are :: $omega - Longitude of the ascending node of the Moons mean; orbit on
the ecliptic, measured from the mean equinox of

date.; $rma - Mean anomaly of the Sun.
$mlanom - Mean anomaly of the Moon.
$F - L - omega, where L is the mean longitude of the; Moon.
$D - Mean elongation of the Moon from the Sun.
$eps0 - Mean obilquity of the ecliptic.
nutate
($deps, $dpsi, @nu) = nutate($omega, $F, $D, $rma, $mlanom,
$eps0);
To calculate the nutation in longitude and obliquity according
to the 1980 IAU Theory of Nutation including terms with amplitudes greater than 0.01 arcsecond. The nutation matrix is used to compute true place from mean place: true vector = N x mean
place vector where the three components of each vector are the direc
tion cosines wrt the mean equinox and equator.: / 1 -dpsi.cos(eps) -dpsi.sin(eps)
N = | dpsi.cos(eps) 1 -deps: dpsi.sin(eps) deps 1 /
The required inputs are : (NOTE: these are the values returned
by ephem_vars): $omega - Longitude of the ascending node of the Moons mean; orbit on
the ecliptic, measured from the mean equinox of

date.; $rma - Mean anomaly of the Sun.
$mlanom - Mean anomaly of the Moon.
$F - L - omega, where L is the mean longitude of the; Moon.
$D - Mean elongation of the Moon from the Sun.
$eps0 - Mean obilquity of the ecliptic.
The returned values are :: $deps - nutation in obliquity
$dpsi - nutation in longitude (scalar)
@nu - nutation matrix (array [3][3])
precsn
@gp = precsn($jd_start, $jd_stop);
To calculate the precession matrix P for dates AFTER 1984.0 (JD
= 2445700.5) Given the position of an object referred to the
equator and equinox of the epoch $jd_start its position referred to the equator and equinox of epoch $jd_stop can be calculated as fol
lows :
1) Express the position as a direction cosine 3-vector (V1): (use pol2r to do this).
2) The corresponding vector V2 for epoch jd_end is V2 = P.V1
The required inputs are :: $jd_start - The Julian day of the current epoch of the coor; dinates.
$jd_end - The Julian day at the required epoch for the con; version.
The returned values are :: @gp - The required precession matrix (array [3][3])
coord_convert
($output_left, $output_right) = coord_convert($input_left, $in
put_right,: $input_mode,; $output_mode,
$mjd, $longitude,; $latitude,
$ref0);
A routine for converting between any of the following coordi
nate systems :: Coordinate system in; put/output mode
----------------; ----------------
X, Y (East-West mounted) 0 Azimuth, Elevation 1 Hour Angle, Declination 2 Right Ascension, Declination (date, J2000 or B1950)
3,4,5 Galactic (B1950) 6
The last four parameters in the call ($mjd, $longitude, $lati
tude and $ref0) are not always required for the coordinate conver
sion. In particular if the conversion is between two coordinate sys
tems which are fixed with respect to the celestial sphere (RA/Dec
J2000, B1950 or Galactic), or two coordinate systems which are fixed
with respect to the antenna (X/Y and Az/El) then these parameters
are not used (NOTE: they must always be passed, even if they only hold
0 or undef as the routine will return undef if it is not passed 8 parameters). The RA/Dec date system is defined with respect to
the celestial sphere, but varies with time. The table below shows
which of $mjd, $longitude, $latitude and $ref0 are used for a given conversion. If in doubt you should determing the correct val
ues for all input parameters, no checking is done in the routine that
the passed values are sensible.: Conversion $mjd $longitude $lati; tude $ref0
-----------------------------------------------------------------------Galactic, Galactic, RA/Dec J2000,B1950 <->RA/Dec J2000, B1950 N N N
N
Galactic, RA/Dec J2000,B1950 <->RA/Dec date Y N N
N
Galactic, RA/Dec J2000,B1950,<->HA/Dec Y Y N
N date
Galactic, RA/Dec J2000,B1950,<->X/Y, Az/El Y Y Y
Y date
X/Y, Az/El <->X/Y, Az/El N N N
N
X/Y, Az/El <->HA/Dec N N Y
Y
NOTE : The method used for refraction correction is asymptotic
at: an elevation of 0 degrees.
The required inputs are :: $input_left - The left/longitude input coordinate (turns)
$input_right - The right/latitude input coordinate (turns)
$input_mode - The mode of the input coordinates (0-6)
$output_mode - The mode to convert the coordinates to.
$mjd - The time as modified Julian day (if neces; sary) at
which to perform the conversion; $longitude - The longitude of the location/observatory (if; necessary)
at which to perform the conversion (turns); $latitude - The latitude of the location/observatory (if; necessary)
at which to perform the conversion (turns); $ref0 - The refraction constant (if in doubt use; 0.00005).
The returned values are :: $output_left - The left/longitude output coordinate (turns)
$output_right - The right/latitude output coordinate (turns)
haset_ewxy
$haset = haset_ewxy($declination, $latitude, %limits);: This routine takes the $declination of the source, and the; $latitude of the
EWXY mounted antenna and calculates the hour angle at which; the source
will set. It is then trivial to calculate the time until the; source
sets, simply by subtracting the current hour angle of the; source from
the hour angle at which it sets.
The required inputs are :: $declination - The declination of the source (turns)
$latitude - The latitude of the observatory (turns)
%limits - A reference to a hash holding the EWXY antenna; limits
The following keys must be defined XLOW,

XLOW_KEYHOLE,
XHIGH, XHIGH_KEYHOLE, YLOW, YLOW_KEYHOLE,

YHIGH,
YHIGH_KEYHOLE (all values shoule be in turns)
The returned value is :: $haset - The hour angle (turns) at which a source at; this
declination sets for an EWXY mounted antenna

with the
given limits at the given latitude
NOTE: returns undef if %limits hash is missing any of the re
quired keys
ewxy_tlos
$tlos = ewxy_tlos($hour_angle, $declination, $latitude, %lim
its);
This routine calculates the time left on-source (tlos) for a
source at $hour_angle, $declination for an EWXY mount antenna at $lat
itude.
The required inputs are :: $hour_angle - The current hour angle of the source (turns)
$declination - The declination of the source (turns)
$latitude - The latitude of the observatory (turns)
limits - A reference to a hash holding the EWXY antenna; limits
The following keys must be defined XLOW,

XLOW_KEYHOLE,
XHIGH, XHIGH_KEYHOLE, YLOW, YLOW_KEYHOLE,

YHIGH,
YHIGH_KEYHOLE (all values should be in turns)
The returned value is :: $tlos - The time left on-source (turns)
haset_azel
$haset = haset_azel($declination, $latitude, %limits);: This routine takes the $declination of the source, and the
$latitude of the Az/El mounted antenna and calculates the hour
angle at which the source will set. It is then trivial to
calculate the time until the source sets, simply by subtract; ing the
current hour angle of the source from the hour angle at which; it
sets. This routine assumes that the antenna is able to rotate
through 360 degrees in azimuth.
The required inputs are :: $declination - The declination of the source (turns)
$latitude - The latitude of the observatory (turns)
limits - A reference to a hash holding the Az/El antenna; limits
The following keys must be defined ELLOW (all

values should
be in turns)
The returned value is :: $haset - The hour angle (turns) at which a source at; this
declination sets for an Az/El mounted antenna

with the
given limits at the given latitude
NOTE: returns undef if the %limits hash is missing any of the
required keys
azel_tlos
$tlos = azel_tlos($hour_angle, $declination, $latitude, lim
its);
This routine calculates the time left on-source (tlos) for a
source at $hour_angle, $declination for an Az/El mount antenna at
$latitude.
The required inputs are :: $hour_angle - The current hour angle of the source (turns)
$declination - The declination of the source (turns)
$latitude - The latitude of the observatory (turns)
%limits - A reference to a hash holding the Az/El antenna; limits
The following keys must be defined ELLOW (all

values
should be in turns)
The returned value is :: $tlos - The time left on-source (turns)
antenna_rise
$ha_set = antenna_rise($declination, $latitude, $mount, lim
its);: Given the $declination of the source, the $latitude of the an; tenna,
the type of the antenna $mount and a reference to a hash hold; ing
information on the antenna limits, this routine calculates the; hour
angle at which the source sets for the antenna. The hour an; gle at
which it rises is simply the negative of that at which it; sets.
These values in turn can be used to calculate the LMST at; which the
source rises/sets and from that the UT at which the source
rises/sets on a given day, or to calculate the native coordi; nates
at which the source rises/sets.; If you want to calculate source rise times above arbitrary el; evation,
use the routine rise.
The required inputs are :: $declination - The declination of the source (turns)
$latitude - The latitude of the observatory (turns)
$mount - The type of antenna mount, 0 => EWXY mount, 1; => Az/El,
any other number will cause the routine to re

turn
undef; %limits - A reference to a hash holding the antenna lim; its
For an EWXY antenna there must be keys for all

the
limits (i.e. XLOW, XLOW_KEYHOLE, XHIGH,

XHIGH_KEYHOLE,
YLOW, YLOW_KEYHOLE, YHIGH, YHIGH_KEYHOLE).

For an Az/El
antenna there must be a key for ELLOW (all

values should
be in turns).
The returned values are :: $ha_set - The hour angle at which the source sets (turns).; The hour
angle at which the source rises is simply the neg

ative of this
value.

docs.sk

comprehensive documentation repository