The surface gravity, g, of an astronomical or other object is the gravitational acceleration experienced at its surface. The surface gravity may be thought of as the acceleration caused by the gravity experienced by a hypothetical test particle which is very close to the object's surface and which, in order not to disturb the system, has negligible mass.
Surface gravity is measured in units of acceleration, which, in the SI system, are meters per second squared. It may also be described as a multiple of the Earth's gravity, g = 9.80665 m/s2. In astrophysics, the surface gravity may be expressed as log g, which is obtained by first expressing the gravity in cgs units, where the unit of acceleration is centimeters per second squared, and then taking the base 10 logarithm.
- p. 29, The International System of Units (SI) Archived 2007-10-31 at the Wayback Machine, ed. Barry N. Taylor, NIST Special Publication 330, 2001.
- Smalley, B. (July 13, 2006). "The Determination of Teff and log g for B to G stars". Keele University. Retrieved 2007-05-31.