The Hertzsprung-Russell (H-R) Diagram

The Hertzsprung-Russell Diagram

The Hertzsprung–Russell Diagram (H-R Diagram) is a scatter graph that depicts the relationship between the absolute magnitudes or luminosities of stars against their stellar classifications or effective temperatures.
Main Sequence Stars comprise the majority of stars and are found along a diagonal band stretching from high temperature & high luminosity (upper left), to low temperature & low luminosity (lower right) on the H-R Diagram.
Red Giants and Supergiants are found above and to the right of the main sequence stars. These are stars that have exhausted their hydrogen fuel and are in a late stage of evolution. They have lower temperatures but high luminosity due to their larger sizes.
White Dwarf Stars are found below and to the left of the main sequence. These are remnants of stars similar to our sun that have shed their outer layers and left behind a hot, dense core. They have high temperatures but low luminosities
The position of a star on the H-R Diagram can tell us about its life stage. The temperature of a star determines its colour, and its luminosity (brightness) tells us about its size and distance.
Supernovae do not appear on the H-R Diagram because their characteristics of brightness and temperature change too rapidly.
Beyond helping to understand stellar evolution, the diagram also enables the estimation of distances to far-away galaxies. This is because it allows astronomers to calculate the intrinsic brightness of a star, which can then be compared to the star’s apparent brightness as seen from Earth to estimate its distance away.
Color index, a measure of the difference in colour a star appears from Earth and its actual colour (which can be affected by things like dust between us and the star), can also be determined using the H-R Diagram. This difference can give an indication of a star’s temperature and can help locate it more specifically on the diagram.