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 void is defined by the absence of stars in the area of the Hertzsprung–Russell diagram, particularly between A5 and G0 spectral types and +1 to −3 absolute magnitudes. This gap lies at the intersection of the main sequence peak and the red giant base for stars with masses above 1.5 solar masses.