An astronomer records a spectrum with a telescope and spectrograph , measures a Doppler shift of a few spectral lines, then calculates a radial velocity. Clever observations have revealed how our solar system moves through space and orbits the center of our galaxy. Astronomers also observe that most objects beyond our galaxy travel away from us at speeds that increase with the object's distance. See also light spectrum Hubble Constant radio galaxy A radio-luminous galaxy .
Radio galaxies are a part of a larger group of galaxies called active galaxies.
Radio telescopes show lobes of radio emission extending millions of light-years , centered at the nucleus of some radio galaxies, called extended radio galaxies. Centaurus A is a nearby example of an extended radio galaxy that features two outer lobes 650,000 and 1,350,000 light-years in diameter. Compact radio galaxies emit radio lobes not much larger that the galactic nucleus. An array of radio telescopes called the Very Large Array lies 80 kilometers west of Soccoro, New Mexico. These radio telescopes probe the galaxy and universe where optical telescopes cannot.