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The Hertzsprung-Russell diagram is an observational tool. The axes are things that can be observed, or at least estimated reasonably well, for most stars (well, those with known distance anyway). We cannot in general measure the masses of stars - only those in some binary systems. The schematic that you show, with an arrow indicating that mass increases ...


Assuming an open model of the universe and a long enough timeline galaxies which appear "normal" today would become more red shifted over the course of observation. I put normal in quotes because there are no galaxies which are relatively static to ours. Any galaxy which has movement will have some "shift" to them, and all galaxies are moving away from us. ...

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