Units
            Length:     m = 10^-4cm = 10⁴Å
                            AU = 1.50x10¹³ cm
                           ly = 0.95x10¹⁸cm
                           pc = 3.09x10¹⁸cm = 2.06x10⁵AU    (2.06x10⁵ arcsec/radian)
            Time:        yr = 3.16x10⁷ s
            Velocity:  pc/Myr = 0.98 km/s
            Energy:     E₀ = 1 eV = 1.60 x10^-12 erg
                                     E₀/k = 1.16x10⁴ K
                                     E₀/h = 2.42x10¹⁴Hz = freq. of 1eV photon
                                     hc/E₀ = 12400Å = 1.24m = wavelength of 1eV photon
                           Ryd = 2.18x10^-11 erg = 13.6 eV
             Flux Density:   1Jy = 10^-23 erg/cm²/s/Hz

Constants
c=3x10¹⁰ cm/s
G = 6.67x10^-8dyn cm² g^-2
e = 4.8x10^-10 esu
h = 6.63x10^-27 erg s              = h/2p = 1.05x10^-27erg s
m_e = 0.91x10^-27 g                  m_ec² = 511keV
m_p = 1.67x10^-24 g                 m_pc² = 0.938GeV
k = 1.38x10^-16 erg/deg = 8.62x10^-5 eV/deg             1keV = 1.16x10⁷ K
a = 7.56x10^-15 erg cm^-3 deg^-4         s = ac/4 = 5.67x10^-5
R = 8.32x10⁷ erg deg^-1 mole^-1
a = e²/= 1/137
= 1.99 x10³³ g        c² = 1.79x10⁵⁴ erg
= 3.90x10³³ erg/s     = 7x10¹⁰cm
H₀ = 70 km/s/Mpc             c/H₀ = 4000 Mpc