It is well known that, due to the general expansion of the universe, all distant extragalactic objects (galaxies, quasars, etc.) are receding from us in space with high speed and that the observed recession velocity increases with distance. In the framework of a cosmological model, the sole measurement of the spectral redshift z of an extragalactic object allows us, in principle, to derive its distance. If the apparent magnitude, angular size, etc., of a given object are also available, it is then possible to determine its absolute magnitude, linear dimensions, etc.