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| author | Joseph Hunkeler <jhunkeler@gmail.com> | 2015-03-04 21:21:30 -0500 |
|---|---|---|
| committer | Joseph Hunkeler <jhunkeler@gmail.com> | 2015-03-04 21:21:30 -0500 |
| commit | d54fe7c1f704a63824c5bfa0ece65245572e9b27 (patch) | |
| tree | afc52015ffc2c74e0266653eecef1c8ef8ba5d91 /src/slalib/sun67.htx/node135.html | |
| download | calfuse-d54fe7c1f704a63824c5bfa0ece65245572e9b27.tar.gz | |
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diff --git a/src/slalib/sun67.htx/node135.html b/src/slalib/sun67.htx/node135.html new file mode 100644 index 0000000..753bc4c --- /dev/null +++ b/src/slalib/sun67.htx/node135.html @@ -0,0 +1,319 @@ +<!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_OAP - Observed to Apparent</TITLE> +<META NAME="description" CONTENT="SLA_OAP - Observed to Apparent"> +<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="node136.html"> +<LINK REL="previous" HREF="node134.html"> +<LINK REL="up" HREF="node13.html"> +<LINK REL="next" HREF="node136.html"> +</HEAD> +<BODY > +<BR> <HR> +<A NAME="tex2html1776" HREF="node136.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html1774" HREF="node13.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html1768" HREF="node134.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="tex2html1777" HREF="node136.html">SLA_OAPQK - Quick Observed to Apparent</A> +<BR> +<B>Up:</B> <A NAME="tex2html1775" HREF="node13.html">SUBPROGRAM SPECIFICATIONS</A> +<BR> +<B> Previous:</B> <A NAME="tex2html1769" HREF="node134.html">SLA_NUTC - Nutation Components</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<H2><A NAME="SECTION0004122000000000000000">SLA_OAP - Observed to Apparent</A> +<A NAME="xref_SLA_OAP"> </A><A NAME="SLA_OAP"> </A> +</H2> + <DL> +<DT><STRONG>ACTION:</STRONG> +<DD>Observed to apparent place. +<DT><STRONG>CALL:</STRONG> +<DD><TT>CALL sla_OAP ( + TYPE, OB1, OB2, DATE, DUT, ELONGM, PHIM, + HM, XP, YP, TDK, PMB, RH, WL, TLR, RAP, DAP)</TT> +<P> </DL> +<P> <DL> +<DT><STRONG>GIVEN:</STRONG> +<DD> +<BR> +<TABLE CELLPADDING=3> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>TYPE</EM></TD> +<TH ALIGN="LEFT"><B>C*(*)</B></TH> +<TD ALIGN="LEFT" NOWRAP>type of coordinates - `R', `H' or `A' (see below)</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>OB1</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observed Az, HA or RA (radians; Az is 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>OB2</EM></TD> +<TD ALIGN="LEFT"><B>D</B></TD> +<TD ALIGN="LEFT" NOWRAP>observed zenith distance or <IMG WIDTH="10" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img23.gif" + ALT="$\delta$"> (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>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="$[\,\alpha,\delta\,]$"></TD> +</TR> +</TABLE></DL> +<P> <DL> +<DT><STRONG>NOTES:</STRONG> +<DD><DL COMPACT> +<DT>1. +<DD>Only the first character of the TYPE argument is significant. +`R' or `r' indicates that OBS1 and OBS2 are the observed Right +Ascension and Declination; `H' or `h' indicates that they are + Hour Angle (west +ve) and Declination; anything else (`A' or + `a' is recommended) indicates that OBS1 and OBS2 are Azimuth + (north zero, east is <IMG WIDTH="26" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img22.gif" + ALT="$90^{\circ}$">) and Zenith Distance. (Zenith + distance is used 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>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 + related to the observed <IMG WIDTH="41" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img29.gif" + ALT="$[\,h,\delta\,]$"> via the standard rotation, using + the geodetic latitude (corrected for polar motion), while the + observed HA and RA are related simply through the local + apparent ST. <I>Observed</I> <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> or <IMG WIDTH="41" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img29.gif" + ALT="$[\,h,\delta\,]$"> thus means 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). + By removing from the observed place the effects of + atmospheric refraction and diurnal aberration, the + geocentric apparent <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> is obtained. + <DT>5. +<DD>Frequently, <I>mean</I> rather than <I>apparent</I> + <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> will be required, + in which case further transformations will be necessary. The + sla_AMP <I>etc.</I> routines will convert + the apparent <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> produced + by the present routine into an FK5 J2000 mean place, by + allowing for the Sun's gravitational lens effect, annual + aberration, nutation and precession. Should FK4 B1950 + coordinates be needed, the routines sla_FK524 <I>etc.</I> will also + need to be applied. + <DT>6. +<DD>To convert to apparent <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> the coordinates read from a + real telescope, corrections would have to be applied for + encoder zero points, gear and encoder errors, tube flexure, + the position of the rotator axis and the pointing axis + relative to it, non-perpendicularity between the mounting + axes, and finally for the tilt of the azimuth or polar axis + of the mounting (with appropriate corrections for mount + flexures). 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>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. + <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 from the terrestrial pole + can be computed using sla_POLMO. + </DL></DL> +<BR> <HR> +<A NAME="tex2html1776" HREF="node136.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html1774" HREF="node13.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html1768" HREF="node134.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="tex2html1777" HREF="node136.html">SLA_OAPQK - Quick Observed to Apparent</A> +<BR> +<B>Up:</B> <A NAME="tex2html1775" HREF="node13.html">SUBPROGRAM SPECIFICATIONS</A> +<BR> +<B> Previous:</B> <A NAME="tex2html1769" HREF="node134.html">SLA_NUTC - Nutation Components</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> |