Thus the H-R diagram is also called the color-magnitude diagram.
But his resulting diagram, made easier because all the stars in each cluster lie at about the same distance, looked very different from today's H-R diagram, because it had only one diagonal line.
We now know that each star reaches a place on the main sequence depending on its mass, and that it remains essentially there for its normal lifetime --shorter for hotter stars and longer for cooler stars--before it evolves up and to the right on the H-R diagram as the star expands into a giant.
White dwarfs are far from red giants on the H-R diagram. As a red giant ages, it eventually fuses helium into carbon.
An H-R diagram I constructed for M13 from the professional catalogs in the publicly accessible VizieR database (http://vizier.u-strasbg.fr/viz-bin/VizieR) reveals a typical globular plot (facing page).
The first thing to notice is that my H-R diagram for M13 looks similar to the one produced from VizieR.
It is somehow reassuring that I would place myself on the H-R diagram
close to our own, quite average, Sun.
It is well illustrated, and there's a marvelous H-R diagram
on page 26.
Such a sun begins its life somewhere along the H-R diagram's main sequence.
Now this sun has moved onto the H-R diagram's asymptotic giant branch (AGB), and its days as an active star are numbered.
The object shoots across the H-R diagram in a matter of months and, in a triumphant encore, the star once again joins the AGB as a supergiant.
Stars that began with more than six times the Sun's mass then evolve left and right through complicated loops on the H-R diagram
as if in a frenzy to keep up their energy production, and finally they explode as supernovae.