def energ_orb(m1,m2,r):
epo = -grav_const * m1 * m2 * msun_g**<NUM_LIT:2> / (r * rsun_cm)<EOL>return epo<EOL>
Parameters
----------
m1, m2 : float
    M in Msun.
r : float
    Distance in Rsun.

Returns
-------
Epot
    Epot in erg.