RR Lyrae "hole" in the colour-magnitude diagram Hi everyone, can someone explain me the RR Lyrae "hole" (or gap) in the colour-magnitude diagram here--> http://media-2.web.britannica.com/eb-media/22/4422-004-DB07836A.gif I suppose that the reason is because they rapidly evolve during this phase. But I know that, generally speaking, stars rapidly evolve during the first passage on the instability strip (H burning) while the second transit on the strip (He burning) is slower. Hence we can see more variable stars in the He-burnig phase than in the H-burning phase. This is true for Cepheids, but for RR Lyrae (obviously they have not the H-burning phase)? Thank you!