Hertzsprung gap
The Hertzsprung Gap is a feature of the Hertzsprung–Russell diagram for a star cluster. It 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, that portion of the diagram is less densely populated.
Full Hertzsprung–Russell diagrams of the 11,000 Hipparcos mission targets show a handful of stars in that region.
