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Index Page b1950_c

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Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

       b1950_c ( Besselian Date 1950.0 )

       SpiceDouble b1950_c ( void )

#### Abstract

       Return the Julian Date corresponding to Besselian Date 1950.0.

#### Required_Reading

       None.

#### Keywords

       CONSTANTS

#### Brief_I/O

       The function returns the Julian Date corresponding to Besselian
       date 1950.0.

#### Detailed_Input

       None.

#### Detailed_Output

       The function returns 2433282.42345905, the Julian Date corresponding
       to Besselian Date 1950.0 as reported by Lieske [1].

#### Parameters

       None.

#### Exceptions

       Error free.

#### Files

       None.

#### Particulars

       Lieske [1] defines a mapping from Julian Ephemeris Date
       to Besselian:

          BE = 1900. + (JED - 2415020.31352)/365.242198781

       The inverse mapping being:

          JED = (BE - 1900.) * 365.242198781 + 2415020.31352

#### Examples

       The numerical results shown for these examples may differ across
       platforms. The results depend on the SPICE kernels used as
       input, the compiler and supporting libraries, and the machine
       specific arithmetic implementation.

       1) Display the double precision value for the Julian Date
          corresponding to the Besselian date 1950.0.

          Example code begins here.

          /.
             Program b1950_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {
             /.
             Display the B1950 date in 16.8 floating point format
             ./
             printf ( "B1950 date: %16.8f\n", b1950_c() );

             return ( 0 );
          }

          When this program was executed on a Mac/Intel/cc/64-bit
          platform, the output was:

          B1950 date: 2433282.42345905

       2) Convert an input time in UTC format to TDB seconds past the
          following reference epochs:

             - Besselian date 1900 and 1950; and

             - Julian date 1900, 1950, 2000 and 2100.

          Use the LSK kernel below to load the leap seconds and time
          constants required for the conversions.

             naif0012.tls

          Example code begins here.

          /.
             Program b1950_ex2
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {
             /.
             Local constants.
             ./
             #define        UTCSTR        "1991-NOV-26"

             /.
             Local variables.
             ./
             SpiceDouble             et;
             SpiceDouble             jed;

             /.
             Load the LSK file.
             ./
             furnsh_c ( "naif0012.tls" );

             /.
             Convert input UTC string to Ephemeris Time.
             ./
             str2et_c ( UTCSTR, &et );
             printf ( "Input ephemeris time  : %20.3f\n\n", et );

             /.
             Convert the Ephemeris Time to Julian ephemeris date, i.e.
             Julian date relative to TDB time scale.
             ./
             jed = unitim_c ( et, "ET", "JED" );

             /.
             Convert Julian Date to TDB seconds past the reference epochs
             and output the results.
             ./
             printf ( "TDB seconds past B1900: %20.3f\n",
                      ( jed - b1900_c() ) * spd_c()     );
             printf ( "TDB seconds past B1950: %20.3f\n",
                      ( jed - b1950_c() ) * spd_c()     );
             printf ( "TDB seconds past J1900: %20.3f\n",
                      ( jed - j1900_c() ) * spd_c()     );
             printf ( "TDB seconds past J1950: %20.3f\n",
                      ( jed - j1950_c() ) * spd_c()     );
             printf ( "TDB seconds past J2000: %20.3f\n",
                      ( jed - j2000_c() ) * spd_c()     );
             printf ( "TDB seconds past J2100: %20.3f\n",
                      ( jed - j2100_c() ) * spd_c()     );

             return ( 0 );
          }

          When this program was executed on a Mac/Intel/cc/64-bit
          platform, the output was:

          Input ephemeris time  :       -255614341.817

          TDB seconds past B1900:       2900118570.055
          TDB seconds past B1950:       1322272271.321
          TDB seconds past J1900:       2900145658.183
          TDB seconds past J1950:       1322265658.183
          TDB seconds past J2000:       -255614341.817
          TDB seconds past J2100:      -3411374341.817

#### Restrictions

       None.

#### Literature_References

       [1]  J. Lieske, "Precession Matrix Based on IAU (1976) System of
            Astronomical Constants," Astron. Astrophys. 73, 282-284,
            1979.

#### Author_and_Institution

       J. Diaz del Rio     (ODC Space)
       W.L. Taber          (JPL)
       I.M. Underwood      (JPL)
       E.D. Wright         (JPL)

#### Version

       -CSPICE Version 2.0.1, 06-JUL-2021 (JDR)

           Edited the header to comply with NAIF standard. Added
           complete code examples.

       -CSPICE Version 2.0.0, 01-SEP-2005 (EDW)

           This routine now returns the value reported in the Lieske
           paper:

              2433282.42345905

           The same value returned by the FORTRAN SPICELIB routine
           B1950.

           This routine previously returned the value reported in the
           "Explanatory Supplement to the Astronomical Almanac", 1992,
           page 699:

              2433282.423

           The ESAA value describing a truncation of the Lieske value.
           The difference between the two values expressed as seconds
           yields approximately 39.662 seconds.

       -CSPICE Version 1.0.1, 08-FEB-1998 (EDW)

           Corrected and clarified header entries.

       -CSPICE Version 1.0.0, 25-OCT-1997 (EDW) (WLT) (IMU)

#### Index_Entries

       besselian date 1950.0

#### Link to routine b1950_c source file b1950_c.c

    Fri Dec 31 18:41:01 2021