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b1900_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

```   b1900_c ( Besselian Date 1900.0 )

SpiceDouble b1900_c ( void )

```

Abstract

```   Return the Julian Date corresponding to Besselian Date 1900.0.
```

```   None.
```

Keywords

```   CONSTANTS

```

Brief_I/O

```   The function returns the Julian Date corresponding to Besselian
date 1900.0.
```

Detailed_Input

```   None.
```

Detailed_Output

```   The function returns 2415020.31352, the Julian Date corresponding
to Besselian Date 1900.0 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 1900.0.

Example code begins here.

/.
Program b1900_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{
/.
Display the B1900 date in 16.8 floating point format
./
printf ( "B1900 date: %16.8f\n", b1900_c() );

return ( 0 );
}

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

B1900 date: 2415020.31352000

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 b1900_ex2
./
#include <stdio.h>
#include "SpiceUsr.h"

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

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

/.
./
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 1.1.1, 06-JUL-2021 (JDR)

complete code examples.

-CSPICE Version 1.1.0, 01-SEP-2005 (EDW)

Added journal reference and associated citations.

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

```   besselian date 1900.0
`Fri Dec 31 18:41:01 2021`