A correlation between the surface brightness of a star at visual wavelengths and the star's (V – R) colour as measured in Johnson photometry. The correlation is independent of the star's luminosity class and nearly independent of interstellar absorption. The relationship allows the angular diameter of any star to be found from its V magnitude and (V – R) colour and is used in measuring the distance to pulsating variables by the Baade–Wesselink method and also the distances of novae and eclipsing binaries. It is named after the American astronomer Thomas Grady Barnes III (1944– ) and the Welsh astronomer David Stanley Evans (1916–2004), who first published it in 1976.
Subjects: Astronomy and Astrophysics.