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b1950_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

```   b1950_c ( Besselian Date 1950.0 )

SpiceDouble b1950_c ( void )

```

#### Abstract

```   Return the Julian Date corresponding to Besselian Date 1950.0.
```

```   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;

/.
./
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)

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)

```   besselian date 1950.0
`Fri Dec 31 18:41:01 2021`