  Conformal gravity theory can explain observed flat rotation curves of
galaxies without invoking hypothetical dark matter. Within this theory, we
obtain a generic formula for the sizes of galaxies exploiting the stability
criterion of circular orbits. It is found that different galaxies have
different finite sizes uniquely caused by the assumed quadratic potential of
cosmological origin. Observations on where circular orbits might actually
terminate could thus be very instructive in relation to the galactic sizes
predicted here.
