Main sequence
type: Concept
broader: Hertzsprung Russell diagram

Instability strip
type: Concept
broader: Hertzsprung Russell diagram

Zero-age horizontal branch stars
type: Concept
related: Hertzsprung Russell diagram

Stellar evolutionary models
type: Concept
narrower: Hertzsprung Russell diagram

Hertzsprung Russell diagram
narrower: Main sequence
narrower: Instability strip
narrower: Giant branch
narrower: Hertzsprung gap
narrower: Horizontal branch
narrower: Post-asymptotic giant branch
narrower: Pre-main sequence
narrower: Turnoff point
narrower: Asymptotic giant branch
narrower: Blue loop
modified: 2020-11-09T16:36:26.14Z
modified: 2020-11-09T16:36:16.164Z
related: Henyey track
related: Hayashi track
related: Stellar evolutionary types
related: Stellar physics
related: Zero-age horizontal branch stars
related: Evolved stars
related: Zero-age main sequence stars
contributor: AAS Frey.Katie
alternative label: Hertzsprung/Russell diagrams
alternative label: Color-color diagrams of stars
alternative label: Hertzsprung-Russell diagrams
alternative label: Hertzsprung Russell diagrams
alternative label: H-R diagrams
alternative label: Hertzsprung-Russell diagram
alternative label: Hertzsprung–Russell diagram
alternative label: Color-magnitude diagrams of stars
alternative label: HR diagram
alternative label: HRD
definition: A display of stellar properties using a plot of effective temperature (or instead color or spectral type) along the abscissa versus luminosity (or absolute magnitude). The temperature is plotted in the inverse direction, with high temperatures on the left and low temperatures on the right. On the diagram the majority of stars are concentrated in a diagonal strip running from upper left to lower right, i.e. from high temperature-high luminosity massive stars to low temperature-low luminosity low-mass stars. This feature is known as the main sequence. This is the locus of stars burning hydrogen in their cores (proton-proton chain). The lower edge of this strip, known as the zero age main sequence (ZAMS), designates the positions where stars of different mass first begin to burn hydrogen in their cores. Well below the main sequence there is a group of stars that, despite being very hot, are so small that their luminosity is very small as a consequence. These are the class of white dwarfs. These objects represent old and very evolved stars that have shed their outer layers to reveal a very small but extremely hot inner core. They are no longer generating energy but are merely emitting light as they cool (white dwarf cooling track). Stars with high luminosities but relatively low temperatures occupy a wide region above the main sequence. The majority of them have used up all the hydrogen in their cores and have expanded and cooled as a result of internal readjustment. Called red giants, they are still burning helium in their cores (helium burning, carbon burning). There are also stars with very high luminosities, resulting from their enormous outputs of energy, because they are burning their fuel at a prodigious rate. These are the supergiants. They can be hot or cool, hence blue or red in color.
type: Concept
broader: Stellar evolutionary models

Pre-main sequence
type: Concept
broader: Hertzsprung Russell diagram

Blue loop
type: Concept
broader: Hertzsprung Russell diagram

Hertzsprung gap
type: Concept
broader: Hertzsprung Russell diagram

Turnoff point
type: Concept
broader: Hertzsprung Russell diagram

Hayashi track
type: Concept
related: Hertzsprung Russell diagram

Post-asymptotic giant branch
type: Concept
broader: Hertzsprung Russell diagram

Stellar physics
type: Concept
related: Hertzsprung Russell diagram

Evolved stars
type: Concept
related: Hertzsprung Russell diagram

Stellar evolutionary types
type: Concept
related: Hertzsprung Russell diagram

Asymptotic giant branch
type: Concept
broader: Hertzsprung Russell diagram

Horizontal branch
type: Concept
broader: Hertzsprung Russell diagram

Henyey track
type: Concept
related: Hertzsprung Russell diagram

Zero-age main sequence stars
type: Concept
related: Hertzsprung Russell diagram

Giant branch
type: Concept
broader: Hertzsprung Russell diagram