From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/node23.html | 278 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 278 insertions(+) create mode 100644 src/slalib/sun67.htx/node23.html (limited to 'src/slalib/sun67.htx/node23.html') diff --git a/src/slalib/sun67.htx/node23.html b/src/slalib/sun67.htx/node23.html new file mode 100644 index 0000000..dfb0e24 --- /dev/null +++ b/src/slalib/sun67.htx/node23.html @@ -0,0 +1,278 @@ + + + + +SLA_AOPQK - Quick Appt-to-Observed + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: SLA_ATMDSP - Atmospheric Dispersion +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_AOPPAT - Update Appt-to-Obs Parameters +

+

+

SLA_AOPQK - Quick Appt-to-Observed +   +

+
+
ACTION: +
Quick apparent to observed place (but see Note 8, below). +
CALL: +
CALL sla_AOPQK (RAP, DAP, AOPRMS, AOB, ZOB, HOB, DOB, ROB) +

+

+
GIVEN: +
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
RAP,DAPDgeocentric apparent $[\,\alpha,\delta\,]$ (radians)
AOPRMSD(14)star-independent apparent-to-observed parameters:
(1)geodetic latitude (radians)
(2,3)sine and cosine of geodetic latitude
(4)magnitude of diurnal aberration vector
(5)height (metres)
(6)ambient temperature (degrees K)
(7)pressure (mB)
(8)relative humidity (0-1)
(9)wavelength ($\mu{\rm m}$)
(10)lapse rate (degrees K per metre)
(11,12)refraction constants A and B (radians)
(13)longitude + eqn of equinoxes + +``sidereal $\Delta$UT'' (radians)
(14)local apparent sidereal time (radians)
+

+
RETURNED: +
+
+ + + + + + + + + + + + + + + + + + + + + +
AOBDobserved azimuth (radians: N=0, E=$90^{\circ}$)
ZOBDobserved zenith distance (radians)
HOBDobserved Hour Angle (radians)
DOBDobserved Declination (radians)
ROBDobserved Right Ascension (radians)
+

+
NOTES: +
+
1. +
This routine returns zenith distance rather than elevation +in order to reflect the fact that no allowance is made for +depression of the horizon. +
2. +
The accuracy of the result is limited by the corrections for + refraction. Providing the meteorological parameters are + known accurately and there are no gross local effects, the + predicted azimuth and elevation should be within about +

$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.1$ for $\zeta<70^{\circ}$. Even + at a topocentric zenith distance of + $90^{\circ}$, the accuracy in elevation should be better than + 1 arcminute; useful results are available for a further + $3^{\circ}$, beyond which the sla_REFRO routine returns a + fixed value of the refraction. The complementary + routines sla_AOP (or sla_AOPQK) and sla_OAP (or sla_OAPQK) + are self-consistent to better than 1 microarcsecond all over + the celestial sphere. +

3. +
It is advisable to take great care with units, as even + unlikely values of the input parameters are accepted and + processed in accordance with the models used. +
4. +
Apparent $[\,\alpha,\delta\,]$ means the geocentric apparent right ascension + and declination, which is obtained from a catalogue mean place + by allowing for space motion, parallax, precession, nutation, + annual aberration, and the Sun's gravitational lens effect. For + star positions in the FK5 system (i.e. J2000), these effects can + be applied by means of the sla_MAP etc. routines. Starting from + other mean place systems, additional transformations will be + needed; for example, FK4 (i.e. B1950) mean places would first + have to be converted to FK5, which can be done with the + sla_FK425 etc. routines. +
5. +
Observed $[\,Az,El~]$ means the position that would be seen by a + perfect theodolite located at the observer. This is obtained + from the geocentric apparent $[\,\alpha,\delta\,]$ by allowing for Earth + orientation and diurnal aberration, rotating from equator + to horizon coordinates, and then adjusting for refraction. + The $[\,h,\delta\,]$ is obtained by rotating back into equatorial + coordinates, using the geodetic latitude corrected for polar + motion, and is the position that would be seen by a perfect + equatorial located at the observer and with its polar axis + aligned to the Earth's axis of rotation (n.b. not to the + refracted pole). Finally, the $\alpha$ is obtained by subtracting + the h from the local apparent ST. +
6. +
To predict the required setting of a real telescope, the + observed place produced by this routine would have to be + adjusted for the tilt of the azimuth or polar axis of the + mounting (with appropriate corrections for mount flexures), + for non-perpendicularity between the mounting axes, for the + position of the rotator axis and the pointing axis relative + to it, for tube flexure, for gear and encoder errors, and + finally for encoder zero points. Some telescopes would, of + course, exhibit other properties which would need to be + accounted for at the appropriate point in the sequence. +
7. +
The star-independent apparent-to-observed-place parameters + in AOPRMS may be computed by means of the sla_AOPPA routine. + If nothing has changed significantly except the time, the + sla_AOPPAT routine may be used to perform the requisite + partial recomputation of AOPRMS. +
8. +
The ``sidereal $\Delta$UT'' which forms part of AOPRMS(13) + is UT1-UTC converted from solar to + sidereal seconds and expressed in radians. +
9. +
At zenith distances beyond about $76^\circ$, the need for + special care with the corrections for refraction causes a + marked increase in execution time. Moreover, the effect + gets worse with increasing zenith distance. Adroit + programming in the calling application may allow the + problem to be reduced. Prepare an alternative AOPRMS array, + computed for zero air-pressure; this will disable the + refraction corrections and cause rapid execution. Using + this AOPRMS array, a preliminary call to the present routine + will, depending on the application, produce a rough position + which may be enough to establish whether the full, slow + calculation (using the real AOPRMS array) is worthwhile. + For example, there would be no need for the full calculation + if the preliminary call had already established that the + source was well below the elevation limits for a particular + telescope. +
10. +
The azimuths etc. used by the present routine are with + respect to the celestial pole. Corrections to the terrestrial pole + can be computed using sla_POLMO. +
+
+ +next + +up + +previous +
+ Next: SLA_ATMDSP - Atmospheric Dispersion +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_AOPPAT - Update Appt-to-Obs Parameters +

+

+

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +
+ + -- cgit