#include <stdio.h>

#include <gsl/gsl_const_mksa.h>

int

main (void)

{

  double c  = GSL_CONST_MKSA_SPEED_OF_LIGHT;

  double au = GSL_CONST_MKSA_ASTRONOMICAL_UNIT;

  double minutes = GSL_CONST_MKSA_MINUTE;

  /* distance stored in meters */

  double r_earth = 1.00 * au;  

  double r_mars  = 1.52 * au;

  double t_min, t_max;

  t_min = (r_mars - r_earth) / c;

  t_max = (r_mars + r_earth) / c;

  printf ("light travel time from Earth to Mars:\n");

  printf ("minimum = %.1f minutes\n", t_min / minutes);

  printf ("maximum = %.1f minutes\n", t_max / minutes);

  return 0;

}