What relationship is plotted on the Hertzsprung-Russell (H-R) diagram to aid in stellar aging?

Answer

Luminosity against temperature (or color)

The H-R diagram maps a star's brightness (luminosity) against its surface temperature or color. A star's position on this map indicates its evolutionary stage relative to its mass.

What relationship is plotted on the Hertzsprung-Russell (H-R) diagram to aid in stellar aging?
ageSpaceastronomysciencestarsstellar evolutionage determination