Top-left: track of evolution of stars from 0.4 to 1.4 M_⊙ in the Hertzsprung-Russell diagram that gives the luminosity (L) as a function of effective temperature (T_eff) (red, orange, green, dark blue, and cyan lines correspond to M-, K-, G-, F-, and A-type stars, respectively). Top-right: evolution of the stellar radius R_s of stars from 0.4 to 1.4 M_⊙ as a function of time. Bottom-left: evolution of the radius aspect ratio α = R_c/R_s of stars from 0.4 to 1.4 M_⊙ as a function of time. Bottom-right: evolution of the mass aspect ratio β = M_c/M_s of stars from 0.4 to 1.4 M_⊙ as a function of time.