While main sequence stars trace a diagonal line on the H-R diagram, red giant stars create a horizontal line in varying shades of red. This is called the red giant branch.

Most stars are main sequence stars that fuse hydrogen to form helium in their cores - including our sun.

At the other end, the upper left of the H-R diagram is the home of the brightest, hottest, most massive main-sequence stars. But how massive can they get?

If there were a branch for white main sequence stars, he and I would be in a dead heat. Next up, I hope: a space-time diagram showing warping due to massive astronomers.

The HR diagram plots stars's luminosity versus temperature, and most stars fall along the main sequence, where they live most of their lives.

Most stars are stable, like the Sun, and fall into the Main Sequence of the plot. Some are old, some young, some dying, some dead. And they all have their place in what we now call the ...