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tyear_c

 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.
```

```   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;

/.
./
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)

```   Number of seconds per tropical year
`Fri Dec 31 18:41:14 2021`