What Is The Hertzsrung-Rusell Diagram?

Answer 1

Introduced in 1912 by two astronomers named, logically enough, "Hertzprung" and "Russell"

it is a scattergram that shows, by size, color and luminosity, what has come to be called the "main sequence" of stars (of which our sun is one). It is a slow "S" curve running from upper left to lower right. It also shows red giants and white dwarfs, to the upper right and lower left, respectively.