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

   None.

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

   None.

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

   The function always returns the constant value shown above.

   The following example uses clight_c to determine the one-way
   light-time (tau) to an object whose position relative to an
   observer is contained in pos. The light-time is then used
   to antedate a request for data from the kernel pool:

         tau = vnorm_c ( pos ) / clight_c ();
         bodmat_c ( body, epoch - tau, trans );

   Note that the SPK reader spkez_c returns the one-way
   light time as an output,

         spkez_c  ( ..., tau );

   None.

   Error free.

   None.

   W.L. Taber      (JPL)
   I.M. Underwood  (JPL)

   None.

   -CSPICE Version 1.0.0, 16-APR-1999 (EDW)

   measured velocity of light in a vacuum