Index of Functions: A B C D E F G H I J K L M N O P Q R S T U V W X
Index Page tyear_c

Table of contents

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

       tyear_c ( Seconds per tropical year )

       SpiceDouble tyear_c ( void )

#### Abstract

       Return the number of seconds in a tropical year.

#### Required_Reading

       None.

#### Keywords

       CONSTANTS

#### Brief_I/O

       The function returns the number of seconds per tropical year.

#### Detailed_Input

       None.

#### Detailed_Output

       The function returns the number of seconds per tropical
       year. This value is taken from the 1992 Explanatory Supplement
       to the Astronomical Almanac (see [1]).

#### Parameters

       None.

#### Exceptions

       Error free.

#### Files

       None.

#### Particulars

       The tropical year is often used as a fundamental unit
       of time when dealing with older ephemeris data. For this
       reason its value in terms of ephemeris seconds is
       recorded in this function.

#### 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 of the number of seconds in a
          tropical year.

          Example code begins here.

          /.
             Program tyear_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {
             /.
             Display the number of seconds in a tropical year,
             in 16.3 floating point format
             ./
             printf ( "Seconds per tropical year: %20.8f\n", tyear_c() );

             return ( 0 );
          }

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

          Seconds per tropical year:    31556925.97470000

       2) Suppose you wish to compute the number of tropical centuries
          that have elapsed since the ephemeris epoch B1950 (beginning
          of the Besselian year 1950) at a particular UTC epoch.

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

             naif0012.tls

          Example code begins here.

          /.
             Program tyear_ex2
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {
             /.
             Local constants.
             ./
             #define        UTCSTR        "2044-JUL-31"

             /.
             Local variables.
             ./
             SpiceDouble             et;
             SpiceDouble             centur;

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

             /.
             Convert input UTC string to Ephemeris Time.
             ./
             str2et_c ( UTCSTR, &et );
             printf ( "Input ephemeris time         : %16.3f\n", et );

             centur = ( et - unitim_c ( b1950_c(), "JED", "ET" ) );
             centur = centur / ( 100.0 * tyear_c() );

             printf ( "Tropical centuries past B1950: %16.10f\n", centur );

             return ( 0 );

          }

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

          Input ephemeris time         :   1406808069.183
          Tropical centuries past B1950:     0.9458128731

#### Restrictions

       None.

#### Literature_References

       [1]  P. Kenneth Seidelmann (Ed.), "Explanatory Supplement to the
            Astronomical Almanac," p 80, University Science Books, 1992.

#### Author_and_Institution

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

#### Version

       -CSPICE Version 1.0.1, 05-JUL-2021 (JDR)

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

       -CSPICE Version 1.0.0, 08-FEB-1998 (EDW) (WLT)

#### Index_Entries

       Number of seconds per tropical year

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

    Fri Dec 31 18:41:14 2021