diff options
Diffstat (limited to 'src/slalib/sun67.htx/node20.html')
| -rw-r--r-- | src/slalib/sun67.htx/node20.html | 320 |
1 files changed, 320 insertions, 0 deletions
diff --git a/src/slalib/sun67.htx/node20.html b/src/slalib/sun67.htx/node20.html new file mode 100644 index 0000000..e544154 --- /dev/null +++ b/src/slalib/sun67.htx/node20.html @@ -0,0 +1,320 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<!--Converted with LaTeX2HTML 97.1 (release) (July 13th, 1997) + by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds +* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan +* with significant contributions from: + Jens Lippman, Marek Rouchal, Martin Wilck and others --> +<HTML> +<HEAD> +<TITLE>SLA_AOP - Apparent to Observed</TITLE> +<META NAME="description" CONTENT="SLA_AOP - Apparent to Observed"> +<META NAME="keywords" CONTENT="sun67"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso_8859_1"> +<LINK REL="STYLESHEET" HREF="sun67.css"> +<LINK REL="next" HREF="node21.html"> +<LINK REL="previous" HREF="node19.html"> +<LINK REL="up" HREF="node13.html"> +<LINK REL="next" HREF="node21.html"> +</HEAD> +<BODY > +<BR> <HR> +<A NAME="tex2html626" HREF="node21.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html624" HREF="node13.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html618" HREF="node19.html"> +<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0" + SRC="contents_motif.gif"></A> +<BR> +<B> Next:</B> <A NAME="tex2html627" HREF="node21.html">SLA_AOPPA - Appt-to-Obs Parameters</A> +<BR> +<B>Up:</B> <A NAME="tex2html625" HREF="node13.html">SUBPROGRAM SPECIFICATIONS</A> +<BR> +<B> Previous:</B> <A NAME="tex2html619" HREF="node19.html">SLA_AMPQK - Quick Apparent to Mean</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<H2><A NAME="SECTION00047000000000000000">SLA_AOP - Apparent to Observed</A> +<A NAME="xref_SLA_AOP"> </A><A NAME="SLA_AOP"> </A> +</H2> + <DL> +<DT><STRONG>ACTION:</STRONG> +<DD>Apparent to observed place, for optical sources distant from +the solar system. +<P> <DT><STRONG>CALL:</STRONG> +<DD><TT>CALL sla_AOP ( + RAP, DAP, DATE, DUT, ELONGM, PHIM, HM, XP, YP, + TDK, PMB, RH, WL, TLR, AOB, ZOB, HOB, DOB, ROB)</TT> +<P> </DL> +<P> <DL> +<DT><STRONG>GIVEN:</STRONG> +<DD> +<BR> +<TABLE CELLPADDING=3> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>RAP,DAP</EM></TD> +<TH ALIGN="LEFT"><B>D</B></TH> +<TD ALIGN="LEFT" NOWRAP>geocentric apparent <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> (radians)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>DATE</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>UTC date/time (Modified Julian Date, JD-2400000.5)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>DUT</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP><IMG WIDTH="16" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img19.gif" + ALT="$\Delta$">UT: UT1-UTC (UTC seconds)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>ELONGM</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observer's mean longitude (radians, east +ve)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>PHIM</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observer's mean geodetic latitude (radians)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>HM</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observer's height above sea level (metres)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>XP,YP</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>polar motion <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img20.gif" + ALT="$[\,x,y\,]$"> coordinates (radians)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>TDK</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>local ambient temperature (degrees K; std=273.155D0)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>PMB</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>local atmospheric pressure (mB; std=1013.25D0)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>RH</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>local relative humidity (in the range 0D0-1D0)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>WL</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>effective wavelength (<IMG WIDTH="26" HEIGHT="25" ALIGN="MIDDLE" BORDER="0" + SRC="img21.gif" + ALT="$\mu{\rm m}$">, <I>e.g.</I> 0.55D0)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>TLR</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>tropospheric lapse rate (degrees K per metre, +<I>e.g.</I> 0.0065D0)</TD> +</TR> +</TABLE></DL> +<P> <DL> +<DT><STRONG>RETURNED:</STRONG> +<DD> +<BR> +<TABLE CELLPADDING=3> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>AOB</EM></TD> +<TH ALIGN="LEFT"><B>D</B></TH> +<TD ALIGN="LEFT" NOWRAP>observed azimuth (radians: N=0, E=<IMG WIDTH="26" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img22.gif" + ALT="$90^{\circ}$">)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>ZOB</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observed zenith distance (radians)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>HOB</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observed Hour Angle (radians)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>DOB</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observed <IMG WIDTH="10" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img23.gif" + ALT="$\delta$"> (radians)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>ROB</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observed <IMG WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img24.gif" + ALT="$\alpha$"> (radians)</TD> +</TR> +</TABLE></DL> +<P> <DL> +<DT><STRONG>NOTES:</STRONG> +<DD><DL COMPACT> +<DT>1. +<DD>This routine returns zenith distance rather than elevation +in order to reflect the fact that no allowance is made for +depression of the horizon. + <DT>2. +<DD>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 +<P> <IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" + SRC="img25.gif" + ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.1$"> for <IMG WIDTH="56" HEIGHT="27" ALIGN="MIDDLE" BORDER="0" + SRC="img26.gif" + ALT="$\zeta<70^{\circ}$">. Even + at a topocentric zenith distance of + <IMG WIDTH="26" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img22.gif" + ALT="$90^{\circ}$">, the accuracy in elevation should be better than + 1 arcminute; useful results are available for a further + <IMG WIDTH="18" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img27.gif" + ALT="$3^{\circ}$">, 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. + <DT>3. +<DD>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. + <DT>4. +<DD><I>Apparent</I> <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> 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>i.e.</I> J2000), these effects can + be applied by means of the sla_MAP <I>etc.</I> routines. Starting from + other mean place systems, additional transformations will be + needed; for example, FK4 (<I>i.e.</I> B1950) mean places would first + have to be converted to FK5, which can be done with the + sla_FK425 <I>etc.</I> routines. + <DT>5. +<DD><I>Observed</I> <IMG WIDTH="66" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img28.gif" + ALT="$[\,Az,El~]$"> means the position that would be seen by a + perfect theodolite located at the observer. This is obtained + from the geocentric apparent <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> by allowing for Earth + orientation and diurnal aberration, rotating from equator + to horizon coordinates, and then adjusting for refraction. + The <IMG WIDTH="41" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img29.gif" + ALT="$[\,h,\delta\,]$"> 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 (<I>n.b.</I> not to the + refracted pole). Finally, the <IMG WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img24.gif" + ALT="$\alpha$"> is obtained by subtracting + the <I>h</I> from the local apparent ST. + <DT>6. +<DD>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. + <DT>7. +<DD>This routine takes time to execute, due mainly to the + rigorous integration used to evaluate the refraction. + For processing multiple stars for one location and time, + call sla_AOPPA once followed by one call per star to sla_AOPQK. + Where a range of times within a limited period of a few hours + is involved, and the highest precision is not required, call + sla_AOPPA once, followed by a call to sla_AOPPAT each time the + time changes, followed by one call per star to sla_AOPQK. + <DT>8. +<DD>The DATE argument is UTC expressed as an MJD. This is, + strictly speaking, wrong, because of leap seconds. However, + as long as the <IMG WIDTH="16" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img19.gif" + ALT="$\Delta$">UT and the UTC are consistent there + are no difficulties, except during a leap second. In this + case, the start of the 61st second of the final minute should + begin a new MJD day and the old pre-leap <IMG WIDTH="16" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img19.gif" + ALT="$\Delta$">UT should + continue to be used. As the 61st second completes, the MJD + should revert to the start of the day as, simultaneously, + the <IMG WIDTH="16" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img19.gif" + ALT="$\Delta$">UT changes by one second to its post-leap new value. + <DT>9. +<DD>The <IMG WIDTH="16" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img19.gif" + ALT="$\Delta$">UT (UT1-UTC) is tabulated in IERS circulars and + elsewhere. It increases by exactly one second at the end of + each UTC leap second, introduced in order to keep <IMG WIDTH="16" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img19.gif" + ALT="$\Delta$">UT + within <IMG WIDTH="15" HEIGHT="25" ALIGN="MIDDLE" BORDER="0" + SRC="img30.gif" + ALT="$\pm$"><IMG WIDTH="24" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img31.gif" + ALT="$0^{\rm s}\hspace{-0.3em}.9$">. <DT>10. +<DD>IMPORTANT - TAKE CARE WITH THE LONGITUDE SIGN CONVENTION. The + longitude required by the present routine is <B>east-positive</B>, + in accordance with geographical convention (and right-handed). + In particular, note that the longitudes returned by the + sla_OBS routine are west-positive (as in the <I>Astronomical + Almanac</I> before 1984) and must be reversed in sign before use + in the present routine. + <DT>11. +<DD>The polar coordinates XP,YP can be obtained from IERS + circulars and equivalent publications. The + maximum amplitude is about + <IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" + SRC="img32.gif" + ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.3$"> . If XP,YP values + are unavailable, use XP=YP=0D0. See page B60 of the 1988 + <I>Astronomical Almanac</I> for a definition of the two angles. + <DT>12. +<DD>The height above sea level of the observing station, HM, + can be obtained from the <I>Astronomical Almanac</I> (Section J + in the 1988 edition), or via the routine sla_OBS. If P, + the pressure in mB, is available, an adequate + estimate of HM can be obtained from the following expression: + <BLOCKQUOTE><TT>HM=-29.3D0*TSL*LOG(P/1013.25D0)</TT> + </BLOCKQUOTE> + where TSL is the approximate sea-level air temperature in degrees K + (see <I>Astrophysical Quantities</I>, C.W.Allen, 3rd edition, + §52). Similarly, if the pressure P is not known, + it can be estimated from the height of the observing + station, HM as follows: + <BLOCKQUOTE><TT>P=1013.25D0*EXP(-HM/(29.3D0*TSL))</TT> + </BLOCKQUOTE> + Note, however, that the refraction is proportional to the + pressure and that an accurate P value is important for + precise work. + <DT>13. +<DD>The azimuths <I>etc.</I> used by the present routine are with + respect to the celestial pole. Corrections to the terrestrial pole + can be computed using sla_POLMO. + </DL></DL> +<BR> <HR> +<A NAME="tex2html626" HREF="node21.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html624" HREF="node13.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html618" HREF="node19.html"> +<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0" + SRC="contents_motif.gif"></A> +<BR> +<B> Next:</B> <A NAME="tex2html627" HREF="node21.html">SLA_AOPPA - Appt-to-Obs Parameters</A> +<BR> +<B>Up:</B> <A NAME="tex2html625" HREF="node13.html">SUBPROGRAM SPECIFICATIONS</A> +<BR> +<B> Previous:</B> <A NAME="tex2html619" HREF="node19.html">SLA_AMPQK - Quick Apparent to Mean</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<ADDRESS> +<I>SLALIB --- Positional Astronomy Library<BR>Starlink User Note 67<BR>P. T. Wallace<BR>12 October 1999<BR>E-mail:ptw@star.rl.ac.uk</I> +</ADDRESS> +</BODY> +</HTML> |