On an H-R diagram, what is the diagonal area that contains more than 90 percent of all stars called?

The diagonal area on the Hertzsprung-Russell (H-R) diagram that contains more than 90 percent of all stars is known as the Main Sequence. This region runs from the upper left to the lower right of the H-R diagram, representing stars that are in a stable phase of hydrogen burning in their cores.

Stars on the Main Sequence are characterized by the relationship between their luminosity and temperature, with cooler stars located towards the bottom right and hotter, more luminous stars towards the top left. This area is significant because it encompasses the majority of the stars in the universe, including our Sun, which is a typical G-type Main Sequence star.

The Main Sequence is vital for understanding stellar evolution, as it illustrates the lifecycle stage where stars spend most of their existence before transitioning to other stages such as red giants or white dwarfs, depending on their mass.