No matter the axes, the oldest objects fall in the the lower left and rapidly varying objects occupy a special strip.  
No matter the axes, the oldest objects fall in the the lower left and rapidly varying objects occupy a special strip.  The horizontal axis can be B minus V color, spectral class, or effective temperature while the vertical axis can be luminosity or absolute magnitude.  For ten points, another group, the Main Sequence, makes up 90 percent of what astronomical diagram.
No matter the axes, the oldest objects fall in the the lower left and rapidly varying objects occupy a special strip.  
Hertzsprung-Russell diagram