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 

Mp  = mass 
ap  = semimajor axis 
Rp  = radius 
rhop  = density 
Vop  = orbital velocity 
ep  = eccentricity 
J2  = oblateness 
tp  = tilt 

M  = mass 
R  = radius 
a  = Semimajor axis 
rho  = density 
e  = eccentricity 
i  = inclination 
Vo  = Orbital Velocity 
Hr  = Hill Radius 
Ve  = Escape Velocity 
Po  = Orbital Period 
gs  = Surface gravity 
Rsyn  = Synchronous Orbit 
