  Following the coincidence A x atomic year ~ Earth year (s), (A = Avogardo
number, atomic year=a_B/alpha c, a_B=Bohr radius, alpha= fine structure
constant, c=light velocity) and considering the "niche" for alpha, i.e.
180^{-1}<alpha<85^{-1}, the Ecosphere radius is calculated. Key words: Fine
structure constant; Planet orbit radii.
