physconst.h

/*
 * Collection of physical constants.
 */
    /* bolzman constant in cgs */
#define KBOLTZ  1.38e-16
    /* mass of hydrogen atom in grams */
#define MHYDR 1.67e-24
    /* solar mass in grams */
#define MSOLG 1.99e33
    /* G in cgs */
#define GCGS 6.67e-8
    /* kiloparsec in centimeters */
#define KPCCM 3.085678e21
    /* Thompson cross-section (cm^2) */
#define SIGMAT 6.6524e-25
    /* Speed of Light cm/s */
#define LIGHTSPEED 2.9979e10

#define SECONDSPERYEAR   31557600.