Editing Red-giant branch (section)

{{Short description|Portion of the giant branch before helium ignition}}
[[File:M5 colour magnitude diagram.png|thumb|right|upright=1.4|[[Hertzsprung–Russell diagram]] for [[globular cluster]] [[Messier 5|M5]]. The red-giant branch runs from the thin horizontal [[subgiant]] branch to the top right, with a number of the more luminous RGB stars marked in red.]]
The '''red-giant branch''' (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of [[stellar evolution]]. It is a stage that follows the [[main sequence]] for low- to intermediate-mass stars. Red-giant-branch stars have an inert [[helium]] core surrounded by a shell of [[hydrogen]] fusing via the [[CNO cycle]]. They are K- and M-class  much larger and more luminous than main-sequence stars of the same temperature.