Talk:Hertzsprung gap

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Shell hydrogen burning starts only when helium core ignites (see for ex. []) (core collapses and the outer layers expand) Orionus 19:38, 3 August 2006 (UTC)

That simply isn't true. The red giant branch, which occurs before core helium fusion, is powered by hydrogen shell fusion. See page 242 in An Introduction to Stellar Astrophysics by LeBlanc. The Hertzsprung Gap is in between core hydrogen burning and hydrogen shell burning, and I will make that correction accordingly. - Anonymous

On the other hand I am not sure, if it is "feature of the HR diagram for a star cluster". Hertzsprung plotted this diagramm for all stars. And I think he noticed the scarcity of stars in that region (now - the gap). But I should check original sources in order to state so. Orionus 19:47, 3 August 2006 (UTC)

The page now reads: "When a star during its evolution crosses the Hertzsprung gap, it means that it has finished core hydrogen burning but has not yet started hydrogen shell burning." The book I am using for studying the evolution of stars (Benacquista, 2013) says: "..... during this phase, the matter below the hydrogen burning shell is collapsing while the matter above it is expanding. This stage where the bulk of luminosity arises from the collapse of the core happens quickly (10^6 years) and so it is rare to observe starts at this point in their evolution off the main sequence over to the red giant phase. This region of the Hertzsprung-Russell diagram is called the Hertzsprung-gap". I therefore deleted this sentence. Saartje39 (talk) 11:10, 26 March 2015 (UTC)