1 /*
2 *+
3 * Name:
4 * palAop
5
6 * Purpose:
7 * Apparent to observed place
8
9 * Language:
10 * Starlink ANSI C
11
12 * Type of Module:
13 * Library routine
14
15 * Invocation:
16 * void palAop ( double rap, double dap, double date, double dut,
17 * double elongm, double phim, double hm, double xp,
18 * double yp, double tdk, double pmb, double rh,
19 * double wl, double tlr,
20 * double *aob, double *zob, double *hob,
21 * double *dob, double *rob );
22
23 * Arguments:
24 * rap = double (Given)
25 * Geocentric apparent right ascension
26 * dap = double (Given)
27 * Geocentirc apparent declination
28 * date = double (Given)
29 * UTC date/time (Modified Julian Date, JD-2400000.5)
30 * dut = double (Given)
31 * delta UT: UT1-UTC (UTC seconds)
32 * elongm = double (Given)
33 * Mean longitude of the observer (radians, east +ve)
34 * phim = double (Given)
35 * Mean geodetic latitude of the observer (radians)
36 * hm = double (Given)
37 * Observer's height above sea level (metres)
38 * xp = double (Given)
39 * Polar motion x-coordinates (radians)
40 * yp = double (Given)
41 * Polar motion y-coordinates (radians)
42 * tdk = double (Given)
43 * Local ambient temperature (K; std=273.15)
44 * pmb = double (Given)
45 * Local atmospheric pressure (mb; std=1013.25)
46 * rh = double (Given)
47 * Local relative humidity (in the range 0.0-1.0)
48 * wl = double (Given)
49 * Effective wavelength (micron, e.g. 0.55)
50 * tlr = double (Given)
51 * Tropospheric laps rate (K/metre, e.g. 0.0065)
52 * aob = double * (Returned)
53 * Observed azimuth (radians: N=0; E=90)
54 * zob = double * (Returned)
55 * Observed zenith distance (radians)
56 * hob = double * (Returned)
57 * Observed Hour Angle (radians)
58 * dob = double * (Returned)
59 * Observed Declination (radians)
60 * rob = double * (Returned)
61 * Observed Right Ascension (radians)
62
63
64 * Description:
65 * Apparent to observed place for sources distant from the solar system.
66
67 * Authors:
68 * PTW: Patrick T. Wallace
69 * TIMJ: Tim Jenness (JAC, Hawaii)
70 * {enter_new_authors_here}
71
72 * Notes:
73 * - This routine returns zenith distance rather than elevation
74 * in order to reflect the fact that no allowance is made for
75 * depression of the horizon.
76 *
77 * - The accuracy of the result is limited by the corrections for
78 * refraction. Providing the meteorological parameters are
79 * known accurately and there are no gross local effects, the
80 * predicted apparent RA,Dec should be within about 0.1 arcsec
81 * for a zenith distance of less than 70 degrees. Even at a
82 * topocentric zenith distance of 90 degrees, the accuracy in
83 * elevation should be better than 1 arcmin; useful results
84 * are available for a further 3 degrees, beyond which the
85 * palRefro routine returns a fixed value of the refraction.
86 * The complementary routines palAop (or palAopqk) and palOap
87 * (or palOapqk) are self-consistent to better than 1 micro-
88 * arcsecond all over the celestial sphere.
89 *
90 * - It is advisable to take great care with units, as even
91 * unlikely values of the input parameters are accepted and
92 * processed in accordance with the models used.
93 *
94 * - "Apparent" place means the geocentric apparent right ascension
95 * and declination, which is obtained from a catalogue mean place
96 * by allowing for space motion, parallax, precession, nutation,
97 * annual aberration, and the Sun's gravitational lens effect. For
98 * star positions in the FK5 system (i.e. J2000), these effects can
99 * be applied by means of the palMap etc routines. Starting from
100 * other mean place systems, additional transformations will be
101 * needed; for example, FK4 (i.e. B1950) mean places would first
102 * have to be converted to FK5, which can be done with the
103 * palFk425 etc routines.
104 *
105 * - "Observed" Az,El means the position that would be seen by a
106 * perfect theodolite located at the observer. This is obtained
107 * from the geocentric apparent RA,Dec by allowing for Earth
108 * orientation and diurnal aberration, rotating from equator
109 * to horizon coordinates, and then adjusting for refraction.
110 * The HA,Dec is obtained by rotating back into equatorial
111 * coordinates, using the geodetic latitude corrected for polar
112 * motion, and is the position that would be seen by a perfect
113 * equatorial located at the observer and with its polar axis
114 * aligned to the Earth's axis of rotation (n.b. not to the
115 * refracted pole). Finally, the RA is obtained by subtracting
116 * the HA from the local apparent ST.
117 *
118 * - To predict the required setting of a real telescope, the
119 * observed place produced by this routine would have to be
120 * adjusted for the tilt of the azimuth or polar axis of the
121 * mounting (with appropriate corrections for mount flexures),
122 * for non-perpendicularity between the mounting axes, for the
123 * position of the rotator axis and the pointing axis relative
124 * to it, for tube flexure, for gear and encoder errors, and
125 * finally for encoder zero points. Some telescopes would, of
126 * course, exhibit other properties which would need to be
127 * accounted for at the appropriate point in the sequence.
128 *
129 * - This routine takes time to execute, due mainly to the
130 * rigorous integration used to evaluate the refraction.
131 * For processing multiple stars for one location and time,
132 * call palAoppa once followed by one call per star to palAopqk.
133 * Where a range of times within a limited period of a few hours
134 * is involved, and the highest precision is not required, call
135 * palAoppa once, followed by a call to palAoppat each time the
136 * time changes, followed by one call per star to palAopqk.
137 *
138 * - The DATE argument is UTC expressed as an MJD. This is,
139 * strictly speaking, wrong, because of leap seconds. However,
140 * as long as the delta UT and the UTC are consistent there
141 * are no difficulties, except during a leap second. In this
142 * case, the start of the 61st second of the final minute should
143 * begin a new MJD day and the old pre-leap delta UT should
144 * continue to be used. As the 61st second completes, the MJD
145 * should revert to the start of the day as, simultaneously,
146 * the delta UTC changes by one second to its post-leap new value.
147 *
148 * - The delta UT (UT1-UTC) is tabulated in IERS circulars and
149 * elsewhere. It increases by exactly one second at the end of
150 * each UTC leap second, introduced in order to keep delta UT
151 * within +/- 0.9 seconds.
152 *
153 * - IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
154 * The longitude required by the present routine is east-positive,
155 * in accordance with geographical convention (and right-handed).
156 * In particular, note that the longitudes returned by the
157 * palObs routine are west-positive, following astronomical
158 * usage, and must be reversed in sign before use in the present
159 * routine.
160 *
161 * - The polar coordinates XP,YP can be obtained from IERS
162 * circulars and equivalent publications. The maximum amplitude
163 * is about 0.3 arcseconds. If XP,YP values are unavailable,
164 * use XP=YP=0.0. See page B60 of the 1988 Astronomical Almanac
165 * for a definition of the two angles.
166 *
167 * - The height above sea level of the observing station, HM,
168 * can be obtained from the Astronomical Almanac (Section J
169 * in the 1988 edition), or via the routine palObs. If P,
170 * the pressure in millibars, is available, an adequate
171 * estimate of HM can be obtained from the expression
172 *
173 * HM ~ -29.3*TSL*LOG(P/1013.25).
174 *
175 * where TSL is the approximate sea-level air temperature in K
176 * (see Astrophysical Quantities, C.W.Allen, 3rd edition,
177 * section 52). Similarly, if the pressure P is not known,
178 * it can be estimated from the height of the observing
179 * station, HM, as follows:
180 *
181 * P ~ 1013.25*EXP(-HM/(29.3*TSL)).
182 *
183 * Note, however, that the refraction is nearly proportional to the
184 * pressure and that an accurate P value is important for precise
185 * work.
186 *
187 * - The azimuths etc produced by the present routine are with
188 * respect to the celestial pole. Corrections to the terrestrial
189 * pole can be computed using palPolmo.
190
191 * History:
192 * 2012-08-25 (TIMJ):
193 * Initial version
194 * Adapted with permission from the Fortran SLALIB library.
195 * {enter_further_changes_here}
196
197 * Copyright:
198 * Copyright (C) 2005 Patrick T. Wallace
199 * Copyright (C) 2012 Science and Technology Facilities Council.
200 * All Rights Reserved.
201
202 * Licence:
203 * This program is free software; you can redistribute it and/or
204 * modify it under the terms of the GNU General Public License as
205 * published by the Free Software Foundation; either version 3 of
206 * the License, or (at your option) any later version.
207 *
208 * This program is distributed in the hope that it will be
209 * useful, but WITHOUT ANY WARRANTY; without even the implied
210 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
211 * PURPOSE. See the GNU General Public License for more details.
212 *
213 * You should have received a copy of the GNU General Public License
214 * along with this program; if not, write to the Free Software
215 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
216 * MA 02110-1301, USA.
217
218 * Bugs:
219 * {note_any_bugs_here}
220 *-
221 */
222
223 #include "pal.h"
224
palAop(double rap,double dap,double date,double dut,double elongm,double phim,double hm,double xp,double yp,double tdk,double pmb,double rh,double wl,double tlr,double * aob,double * zob,double * hob,double * dob,double * rob)225 void palAop ( double rap, double dap, double date, double dut,
226 double elongm, double phim, double hm, double xp,
227 double yp, double tdk, double pmb, double rh,
228 double wl, double tlr,
229 double *aob, double *zob, double *hob,
230 double *dob, double *rob ) {
231
232 double aoprms[14];
233
234 palAoppa(date,dut,elongm,phim,hm,xp,yp,tdk,pmb,rh,wl,tlr,
235 aoprms);
236 palAopqk(rap,dap,aoprms,aob,zob,hob,dob,rob);
237
238 }
239