An Etymological Dictionary of Astronomy and Astrophysics

1. The third letter of the Greek alphabet (γ, Γ).
   

2. Symbol used to denote the ratio of the principal specific heats C_P/C_V of a gas, where C_P is the specific heat at constant pressure and C_V that measured at constant volume.
   

3. Unit of magnetic field intensity, equal to 10^-5 gauss.
   

4. The distance of the Moon’s shadow axis from Earth’s center in units of equatorial Earth radii. It is defined at the instant of → greatest eclipse when its absolute value is at a minimum (F. Espenak, NASA).

See also: The third letter of the Gk. alphabet, from Gk. gamma, from Phoenician gimel.