gal

Gal is an abbreviation that can refer to several different concepts depending on the context. It is used as a name for a unit of acceleration, a unit of volume, and as a shorthand in astronomy for galaxy, among other uses.

As a unit of acceleration, the Gal (symbol: Gal) equals one centimeter per second squared (1 cm/s²). It is a non-SI unit employed mainly in geophysics and gravimetry to measure small variations in gravity. Named after Galileo Galilei, the Gal is convenient for expressing gravity data on a scale relevant to subsurface features. In practice, gravity measurements are often reported in milligals (mGal) or microgals, where 1 Gal = 0.01 m/s² and 1 mGal = 0.001 Gal.

As a unit of volume, the gallon (abbreviated gal) is used in US customary and imperial systems. A US gallon equals 3.78541 liters, while an imperial gallon equals 4.54609 liters. The gallon appears in contexts like cooking, fuel pricing, and shipping. The exact value depends on whether the measurement follows US or imperial definitions.

In astronomy, gal or gal. is sometimes used as shorthand for galaxy in catalogs and informal writing. This usage is not a formal unit or standard and relies on context to avoid ambiguity. In formal scientific writing, “galaxy” is preferred.

Summary: Gal can denote (1) a unit of acceleration used in gravity measurements, (2) a unit of volume (gallon) with country-specific values, and (3) an informal shorthand for galaxy in astronomy. The intended meaning is usually clear from the surrounding text.