Local standard of rest

In astronomy, the local standard of rest (LSR) is a reference frame which follows the mean motion of material in the Milky Way in the neighborhood of the Sun (stars in radius 100 pc from the Sun),^[1] on average sharing the same velocity around the Milky Way as the Sun.^[2] The path of this material is not precisely circular.^[3] The Sun follows the solar circle (eccentricitye < 0.1) at a speed of about 255 km/s in a clockwise direction when viewed from the galactic north pole at a radius of ≈ 8.34 kpc^[4] about the center of the galaxy near Sgr A*, and has only a slight motion, towards the solar apex, relative to the LSR.^[5][6]

LSR could be understood by analogy to a group of cars traveling at similar speed on a highway i.e. at LSR. If a faster car passes by or they pass a slower car then the faster and slower cars could be considered at not traveling at LSR.

The LSR velocity is anywhere from 202–241 km/s.^[7] In 2014, very-long-baseline interferometry observations of maser emission in high-mass star-forming regions (HMSFR) placed tight constraints on combinations of kinematic parameters such as the circular orbit speed of the Sun (Θ₀ + V_☉ = 255.2 ± 5.1 km/s).^[4] There is significant correlation between the circular motion of the solar circle, the solar peculiar motion, and the predicted counterrotation of star-forming regions.^[8] Additionally, local estimates of the velocity of the LSR based on stars in the vicinity of the Sun^[9] may potentially yield different results than global estimates derived from motions relative to the Galactic Center.^[10]

• Comoving coordinates for an example of another convenient astronomical reference frame.