Procedure

     CLIGHT ( C, Speed of light in a vacuum )

     DOUBLE PRECISION FUNCTION CLIGHT ( )

Abstract

     Return the speed of light in a vacuum (IAU official
     value, in km/sec).

Required_Reading

     None.

Keywords

     CONSTANTS

Declarations

    None.

Brief_I/O

     The function returns the speed of light in vacuum (km/sec).

Detailed_Input

     None.

Detailed_Output

     The function returns the IAU official value for the speed of light
     in vacuum: 299792.458 km/sec.

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     The function always returns the constant value shown above.

Examples

     Find the light time corresponding to the length of a given
     3-dimensional position vector. Length units are km.

     To use CLIGHT, declare it as having double precision type:

        DOUBLE PRECISION      CLIGHT

     Let POS be a 3-vector of interest; let TAU be the light time.
     VNORM is the SPICELIB function that returns the norm of a
     3-vector.

        DOUBLE PRECISION      VNORM
        DOUBLE PRECISION      TAU
        DOUBLE PRECISION      POS (3 )

     Find the light time:

        TAU = VNORM ( POS ) / CLIGHT ()

     Note that the SPK readers

        SPKEZR
        SPKEZ
        SPKPOS
        SPKEZP

     return the one-way light time between target and observer
     as an output.

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.0.3, 25-AUG-2021 (JDR)

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.0.2, 08-JAN-2008 (NJB)

        $Examples section was updated to remove references to SPKAPP
        and BODMAT.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (WLT) (IMU)