Jpl horizons algorithm delta t #4673

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open

ssimard2504 wants to merge 12 commits into Stellarium:master from ssimard2504:JPL_horizons_algorithm_deltaT

+59,263 −83

.gitattributes

Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		ephem/*.430t filter=lfs diff=lfs merge=lfs -text
		ephem/*.440t filter=lfs diff=lfs merge=lfs -text

guide/app_acknowledgements.tex

-Original file line number
+Diff line change
@@ Expand Up / @@ -176,6 +176,7 @@ \section{Technical Articles} @@
     		\item \citetp{Montenbruck-Pfleger:2000} % ``Astronomy on the Personal Computer''
     		\item \citetp{Reingold-Dershowitz:2001} %``Calendrical Calculations''
     		\item $\Delta T$ webpage by V. Reijs: \url{http://www.iol.ie/~geniet/eng/DeltaTeval.htm}
+    		\item JPL Horizons System manual: \url{https://ssd.jpl.nasa.gov/horizons/manual.html}
     		\end{enumerate}
     	\item[Precession:] \citetp{2011AA:Vondrak} with correction \citep{2012AA:Vondrak}
     	\item[Nutation:]   \citetp{Nutation:IAU2000B} %Dennis D. McCarthy and Brian J. Luzum: An Abridged Model of the Precession-Nutation of the Celestial Pole.
@@ Expand All / @@ -201,6 +202,7 @@ \section{Included Source Code} @@
       \item OBJ loader in the Scenery3D plugin based on glObjViewer (c) 2007 dhpoware
       \item Parts of the code to work with DE430/DE431 and DE440/DE441 data files have been taken from Project Pluto (GPL license).
       \item The \file{SpoutLibrary.dll} and header from the SpoutSDK version 2.005 available at \url{http://spout.zeal.co} (BSD license).
+      \item Parts of the code to compute $\Delta T$ for JPL Horizons algorithm\newFeature{26.1} requires access to Essential Routines for Fundamental Astronomy (ERFA, version 2.0.1) (BSD-3-Clause license).
     \end{itemize}
     \section{Data}
@@ Expand Down @@

guide/ch_advanced_use.tex

            
                      Original file line number
                      Diff line number
                      Diff line change
                  
    @@ -315,12 +315,12 @@ \subsection{Alternative Planet Ephemerides: DE430, DE431, DE440, DE441}
  
    JPL\footnote{\url{https://ssd.jpl.nasa.gov/ftp/eph/planets/Linux/} (Also

      download from this directory if you are not running Linux!)}:

    \noindent\begin{tabular}{lllr}

    \newFeature{26.1}\noindent\begin{tabular}{lllr}

    \toprule

    \emph{Ephemeris}&\emph{Filename}& \emph{MD5 hash}& \emph{Size}\\\midrule

    DE430& \file{linux\_p1550p2650.430}  &\texttt{707c4262533d52d59abaaaa5e69c5738}& 97.5\,MB\\

    DE430& \file{linux\_p1550p2650.430t} &\texttt{0da79f08c0f32e68fd5321ee7772256c}& 94.0\,MB\\

    DE431& \file{lnxm13000p17000.431}    &\texttt{fad0f432ae18c330f9e14915fbf8960a}& 2.59\,GB\\

    DE440& \file{linux\_p1550p2650.440}  &\texttt{9dc8a9cefd32b0090002407847e718ba}& 97.5\,MB\\

    DE440& \file{linux\_p1550p2650.440t} &\texttt{5259afc41888b800fa7757b3e4d47829}& 107\,MB\\

    DE441& \file{linux\_m13000p17000.441}&\texttt{4e3b924463d17b68ec9c4a18240300cd}& 2.59\,GB\\\bottomrule

    \end{tabular}

    @@ -332,9 +332,9 @@ \subsection{Alternative Planet Ephemerides: DE430, DE431, DE440, DE441}
  
    \file{config.ini} like:

    \begin{configfile}

    [astro]

    de430_path = C:/Astrodata/JPL_DE43x/linux_p1550p2650.430

    de430_path = C:/Astrodata/JPL_DE43x/linux_p1550p2650.430t

    de431_path = C:/Astrodata/JPL_DE43x/lnxm13000p17000.431

    de440_path = C:/Astrodata/JPL_DE44x/linux_p1550p2650.440

    de440_path = C:/Astrodata/JPL_DE44x/linux_p1550p2650.440t

    de441_path = C:/Astrodata/JPL_DE44x/linux_m13000p17000.441

    \end{configfile}

guide/ch_astronomical_concepts.tex

-Original file line number
+Diff line change
@@ Expand Up / @@ -747,12 +747,19 @@ \subsubsection{List of $\Delta T$ models in Stellarium} @@
       %% TODO: ADD REFERENCE FOR C,C-T,F:1997!
       Valid range of usage: between years -400 and 2150. $\dot{n}=-25.7376''/\cy^2$.
-    \item[JPL HORIZONS.] The JPL Solar System Dynamics Group of the NASA
-      Jet Propulsion Laboratory use this formula in their interactive
-      website JPL
-      HORIZONS\footnote{\url{https://ssd.jpl.nasa.gov/?horizons}}. Valid
-      range of usage: between years -2999 and 1620, with zero values
-      outside this range. $\dot{n}=-25.7376''/\cy^2$.
+    \item[JPL Horizons.]The JPL Solar System Dynamics Group\newFeature{26.1} of the NASA Jet Propulsion
+      Laboratory has developed an interactive application JPL HORIZONS\footnote{\url{https://ssd.jpl.nasa.gov/?horizons}}
+      which provides $\Delta T=TDB-UT$ between -9998 and 1962 and $\Delta T=TDB-UTC$ between 1962 to 9999
+      \footnote{\url{https://ssd.jpl.nasa.gov/horizons/manual.html}}. Stellarium
+      JPL Horizons algorithm emulates the JPL HORIZONS application with differences of less than +/- 0.1 second
+      for historical dates up to 1962, improving to less than +/- 10 microseconds from 1962 to Present time.
+      It is important to note that $\Delta T$ from Present time to year 9999 uses the last EOP
+      (Earth Orientation Parameter) predicted. Therefore, although you can enter dates up to year 9999,
+      $\Delta T$ values beyond Present time are meaningless. The valid range of usage is therefore between years
+      -9998 and Present with invalid $\Delta T$ outside this range. Use of this algorithm ought to be
+      done with the selection of DE44x/DE43x ephemerides files (see section~\ref{sec:ExtraData:ephemerides})
+      otherwise $\Delta T$ value computed by Stellarium will not reproduce results of the JPL HORIZONS application.
+      $\dot{n}=-25.936''/\cy^2$ for DE44x ephemerides and $\dot{n}=-25.82''/\cy^2$ for DE43x ephemerides.
     \item[Meeus \& Simons (2000).] This polynome was published in \citetp{2000JBAA..110..323M}.
       Valid range of usage: between years 1620 and 2000, with zero values outside this
@@ Expand Down @@

src/CMakeLists.txt

-Original file line number
+Diff line change
@@ Expand Up / @@ -528,7 +528,9 @@ IF(ENABLE_SPOUT AND SPOUT_LIBRARY_DLL) @@
          CONFIGURE_FILE(${SPOUT_LIBRARY_DLL} ${CMAKE_CURRENT_BINARY_DIR} COPYONLY)
     ENDIF()
-    SET(STELMAIN_DEPS ${MD4C_STEL_LIBRARIES} ${ZLIB_LIBRARIES} glues_stel ${STELLARIUM_STATIC_PLUGINS_LIBRARIES} ${STELLARIUM_QT_LIBRARIES} ${SPOUT_LIBRARY} ${STD_EXECUTION_LIBS})
+    # (SS) 2025-11-27 - Added erfa_201 to the dependencies
+    # (SS) 2025-12-03 - Changed erfa_201 to erfa
+    SET(STELMAIN_DEPS ${MD4C_STEL_LIBRARIES} ${ZLIB_LIBRARIES} glues_stel erfa ${STELLARIUM_STATIC_PLUGINS_LIBRARIES} ${STELLARIUM_QT_LIBRARIES} ${SPOUT_LIBRARY} ${STD_EXECUTION_LIBS})
     IF(USE_BUNDLED_QTCOMPRESS)
          SET(STELMAIN_DEPS ${STELMAIN_DEPS} qtcompress_stel)
     ENDIF()
@@ Expand Down @@

src/core/StelCore.cpp

            
                      Original file line number
                      Diff line number
                      Diff line change
                  
    @@ -2352,7 +2352,7 @@ double StelCore::getDeltaT() const
  
    	return JD.second;

    }

    // (SS) 2025-11-27 : REVISED for differentiating between DE430/431 and DE440/441 ephemeris selection in Moon Secular Acceleration

    // compute and return DeltaT in seconds. Try not to call it directly, current DeltaT, JD, and JDE are available.

    double StelCore::computeDeltaT(const double JD)

    {

    @@ -2374,10 +2374,10 @@ double StelCore::computeDeltaT(const double JD)
  
    	}

    	if (!deltaTdontUseMoon)

    		DeltaT += StelUtils::getMoonSecularAcceleration(JD, deltaTnDot, ((de440Active&&EphemWrapper::jd_fits_de440(JD)) ||

    										 (de441Active&&EphemWrapper::jd_fits_de441(JD)) ||

    										 (de430Active&&EphemWrapper::jd_fits_de430(JD)) ||

    										 (de431Active&&EphemWrapper::jd_fits_de431(JD))));

    		DeltaT += StelUtils::getMoonSecularAcceleration(JD, deltaTnDot,((de430Active && EphemWrapper::jd_fits_de430(JD)) ||

    		                                                                (de431Active && EphemWrapper::jd_fits_de431(JD))),

    		                                                               ((de440Active && EphemWrapper::jd_fits_de440(JD)) ||

    		                                                                (de441Active && EphemWrapper::jd_fits_de441(JD)))); 

    	return DeltaT;

    }

    @@ -2531,11 +2531,19 @@ void StelCore::setCurrentDeltaTAlgorithm(DeltaTAlgorithm algorithm)
  
    			deltaTfinish	=  2150; // 1997;

    			break;

    		case JPLHorizons:

    			// JPL Horizons algorithm for DeltaT

    			deltaTnDot = -25.7376; // n.dot = -25.7376 "/cy/cy

    			// (SS) 2025-11-27 JPL Horizons algorithm for DeltaT - REVISED

    			// From a communication with Jon Giorgini (JPL) 2025-11-12, n.dot value of -25.82"/cy/cy matches

    			// DE430/DE431 Ephemerides and Stephenson/Morrison/Hohenkerk/Zawilski cubic splines.

    			// However, DE440/DE441 Ephemerides use slightly different lunar model, so we need to apply

    			// the moon secular acceleration correction separately in computeDeltaT() when those are selected.

    			// The n.dot value for DE440/DE441 is -25.936"/cy/cy per Jon Giorgini (JPL) 2025-11-12 email.

    			// The JPL Horizons DeltaT model is valid only from 9999BC to Present. JPL Horizons app actually clamps

    			// Delta-T values to the last EOP file predictions for future dates beyond Present while allowing 

    			// JD value up to 9999-12-30 00:00. Just keep in mind that Delta-T values are not valid beyond Present.

    			deltaTnDot = -25.82; // n.dot = -25.82"/cy/cy

    			deltaTfunc = StelUtils::getDeltaTByJPLHorizons;

    			deltaTstart	= -2999;

    			deltaTfinish	= 1620;

    			deltaTstart = -9998; // 9999BC-03-20 00:00 UT --> JD_UT >= -1930633.5, yearFraction >= -9997.786301369860

    			deltaTfinish = 9999; // 9999AD-12-30 00:00 UT --> JD_UT <=  5373482.5, yearFraction <=  9999.994520547950

    			break;

    		case MeeusSimons:

    			// Meeus & Simons (2000) algorithm for DeltaT

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Jpl horizons algorithm delta t #4673

Diff view

Diff view

There are no files selected for viewing

Uh oh!

Uh oh!

Uh oh!

Jpl horizons algorithm delta t #4673

Are you sure you want to change the base?

Jpl horizons algorithm delta t #4673

Uh oh!

Uh oh!

Diff view

Diff view

There are no files selected for viewing

Uh oh!

Uh oh!