Clight = 2.99792458 10^10
Ggrav = 6.6726 10^-8
Hplanck = 6.6260755 10^-27
Echarge = 4.8032068 10^-10
Me = 9.1093898 10^-28
Mp = 1.6726231 10^-24
Mn = 1.6749286 10^-24
Kb = 1.380658 10^-16
Nav = 6.0221367 10^23
Sigmablack = 5.67051 10^-5  (* =  Clight Ablack / 4 *) 
Ablack = 7.56591 10^-15                    (* =  Kb^4 8 Pi^5/(15 Clight^3 Hplanck^3) *) 
SigmaT = 8Pi/3 (Echarge^2/(Me Clight^2))^2 
EV = 1.60217733 10^-12
Lsun = 3.847 10^33
Msun = 1.9891 10^33
Rsun = 6.96 10^10
Teffsun = 5780
Hour = 3600; 
Day = 24 Hour; 
Year=365.25 Day; 
Myr = 10^6 Year
Pc = 3.086 10^18
Au = 1.495979 10^13;
Angstrom = 1*^-8; 

(* from Kittel -- maybe old numbers. *) 
Amu = 1.66057 10^-24

(*derivative quantities*)
Kpc = 1*^3 Pc; 
Mpc = 1*^6 Pc; 
Hbar = Hplanck/(2 Pi)
Reclass = Echarge^2 /(Me Clight^2)
Recompton = Hbar/(Me Clight)
Alphafs = Echarge^2 /(Hbar Clight) 
Rbohr = Hbar^2 /(Me Echarge^2)
Rydberg = Me Echarge^4 /(2 Hbar^2)
Rgas = Nav Kb;
Mh = Mp+Me-13.6EV/Clight^2;
Arcsec = Au/Pc; Mas = Arcsec 10^-6;
Arcmin= 60 Arcsec; 
Rearth = 5800 Km; 
Km = 10^5; 
Kps = Km; 

(* Chandrasekhar mass. Requires mue. 1.4 when mue=2. *) 
Mchandra   := (0.19670190901523182*Clight^(3/2)*Hplanck^(3/2))/(Ggrav^(3/2)*Mh^2*mue^2); 
Mchandra14 := (0.19670190901523182*Clight^(3/2)*Hplanck^(3/2))/(Ggrav^(3/2)*Mh^2*2^2); 

Alpha2 = 3.46*^-13; (* Recombination rate coefficient *)

(* possibly useful for rough error estimates... *)
err := {-1,0,1}; 

(* solve for x such "one" of the form a x^b is = 1... e.g., xOne[B/b, b] gives B. *)
xOne[one_,x_] := x one^(-1/Exponent[one//PowerExpand,x])//PowerExpand ;