local standard of rest (LSR)

The local standard of rest (LSR) is a point in space that has a velocity equal to the average velocity of stars in the solar neighborhood, including the Sun. There are two forms of the local standard of rest.


The dynamical LSR is a point in the vicinity of the Sun which is in a circular orbit around the Galactic center. The Sun's motion with respect to the dynamical LSR is called the peculiar solar motion.


The kinematical LSR, which is the form conventionally used by observational astronomers, is the mean standard of rest of specified star catalogues or stellar populations. The Sun's motion with respect to an agreed kinematical LSR is known as the standard solar motion, defined as the average velocity of spectral types A through G as found in general catalogues of radial velocity, regardless of luminosity class. This motion is 19.5 km/s toward 18 hours right ascension and 30° declination for epoch 1900.0 (galactic coordinates l=56°, b=23°). Basic solar motion is the most probable velocity of stars in the solar neighborhood, so it is weighted more heavily by the radial velocities of stars of the most common spectral types (A, gK, dM) in the solar vicinity. In this system, the Sun moves at 15.4 kilometers per second toward l=51°, b=23°.