The gap is named after Ejnar Hertzsprung, who first noticed the absence of stars in the region of the Hertzsprung–Russell diagram between A5 and G0 spectral type and between +1 and −3 absolute magnitudes. This gap lies between the top of the main sequence and the base of red giants for stars above roughly 1.5 solar mass.
The Ejnar Hertzsprung-named gap is characterized by the absence of stars in the region of the Hertzsprung–Russell diagram, specifically between A5 and G0 spectral types and +1 to −3 absolute magnitudes. This gap falls between the summit of the main sequence and the foundation of red giants for stars with masses greater than 1.5 solar masses.