Lecture 2 Reference Tables

CGS Units & Astrophysical Constants

CGS Unit Reference

Quantity	CGS Unit	Base Units	SI Conversion
Force	dyne	g cm s\(^{-2}\)	\(10^{-5}\) N
Energy	erg	g cm\(^2\) s\(^{-2}\)	\(10^{-7}\) J
Pressure	dyne/cm\(^2\)	g cm\(^{-1}\) s\(^{-2}\)	0.1 Pa
Luminosity	erg/s	g cm\(^2\) s\(^{-3}\)	\(10^{-7}\) W
Flux	erg cm\(^{-2}\) s\(^{-1}\)	g s\(^{-3}\)	\(10^{-3}\) W/m\(^2\)

Fundamental Physical Constants

Constant	Symbol	CGS Value
Gravitational constant	\(G\)	\(6.67 \times 10^{-8}\) cm\(^3\) g\(^{-1}\) s\(^{-2}\)
Speed of light	\(c\)	\(3.0 \times 10^{10}\) cm s\(^{-1}\)
Stefan-Boltzmann	\(\sigma\)	\(5.67 \times 10^{-5}\) erg cm\(^{-2}\) s\(^{-1}\) K\(^{-4}\)
Boltzmann constant	\(k_B\)	\(1.38 \times 10^{-16}\) erg K\(^{-1}\)
Planck constant	\(h\)	\(6.63 \times 10^{-27}\) erg s
Reduced Planck	\(\hbar\)	\(1.05 \times 10^{-27}\) erg s

Astrophysical Constants (Solar Units)

Quantity	Symbol	CGS Value
Solar mass	\(M_\odot\)	\(2.0 \times 10^{33}\) g
Solar radius	\(R_\odot\)	\(7.0 \times 10^{10}\) cm
Solar luminosity	\(L_\odot\)	\(3.8 \times 10^{33}\) erg/s
1 Astronomical Unit	AU	\(1.50 \times 10^{13}\) cm
1 parsec	pc	\(3.09 \times 10^{18}\) cm
1 light-year	ly	\(9.46 \times 10^{17}\) cm

Key Conversions to Memorize

Conversion	Factor
1 J = ? erg	\(10^7\) erg
1 N = ? dyne	\(10^5\) dyne
1 W = ? erg/s	\(10^7\) erg/s
1 m = ? cm	\(10^2\) cm
1 kg = ? g	\(10^3\) g

Dimensional “Recipes”

Quantity	Dimensions
Velocity	\([LT^{-1}]\)
Acceleration	\([LT^{-2}]\)
Force	\([MLT^{-2}]\)
Energy	\([ML^2T^{-2}]\)
Pressure	\([ML^{-1}T^{-2}]\)
Luminosity (Power)	\([ML^2T^{-3}]\)
Gravitational constant \(G\)	\([M^{-1}L^3T^{-2}]\)