Lecture Notes for Astronomy 321, W 2004 1 Stellar Energy ...

expressions for K are accurate, and we will often notationally use E to mean
kinetic energy.
We will borrow the unit system which is customary in atomic, nuclear,
and particle physics. Energy is expressed in units of eV, where
1 eV = 1.60 × 10 −19 J = 1.60 × 10 −12 erg .
Most importantly, we use E 2 = p 2 c 2 +m 2 c 4 to allow us to also write rest mass
and momentum using the eV. So rest mass has units eV/c 2 (more typically
MeV/c 2 ), and momentum eV/c. In this way, we do not usually have to
multiply or divide by the numerical value for c.
1.2 Physical data and conversions
c = 2.9979 × 10 8 m/s
1 eV = 1.60 × 10 −19 J = 1.60 × 10 −12 erg
1 fm = 10 −15 m
¯h = h/2π = 1.054 × 10 −34 J s = 6.58 × 10 −22 MeV s
¯hc = 197 MeV fm
e = 1.60 × 10 −19 C = 4.80 × 10 −10 esu
k = 1.38 × 10 −23 J/K = 8.62 × 10 −11 MeV/K
G = 6.67 × 10 −11 N m 2 / kg 2
α = e 2 /(4πɛ 0¯hc) (in SI) = 1/137
m e c 2 = 0.511 MeV
m p c 2 = 938 MeV
(m n − m p )c 2 = 1.293 MeV
1 u = 931.49432 MeV/c 2
1 pc = 3.086 × 10 16 m = 3.262 ly
M ⊙ = 1.99 × 10 30 kg
L ⊙ = 3.85 × 10 26 W
2