pi  ~ 3.141592654 
G  = gravitational constant 
c  = speed of light 
Msun  = Mass of Sun 
Rsun  = Radius of Sun 
Lsun  = Luminosity of Sun 
m2AU  = meters to AU 
AU2m  = AU to meters 
s2yr  = seconds to years 
s2hr  = seconds to hours 
r2d  = radians to degrees 
d2r  = degrees to radians 

M  = mass 
R  = radius 
rho  = density 
Ve  = escape velocity 
Ps  = spin period 
J2  = oblateness 
Hr  = Hill Radius 
gs  = Surface Gravity 

tilt = tilt 
a  = Semimajor axis 
i  = inclination 
e  = eccentricity 
Po  = orbital period 
Vo  = orbital velocity 
Rsyn  = Synchronous Orbit 
