Physics of the blue-to-red and red-to-blue transitions in the evolution of massive stars .1. From blue to red

The physics of the evolution of massive stars from the main sequence to the red is explored in order to provide an interpretation of the way in which it is affected by several important input physics parameters. The evolutionary effects of the criterion for convection, of the metallicity, of the opacities at intermediate temperatures, of mass loss and of overshoot during the main sequence are illustrated and interpreted.