What is the difference between a seyfert galaxy and a quasar?
Quasars are brighter, more distant and older than Seyfert galaxies.
Both are considered to be active galactic nuclei. Quasars are brighter and more distant objects (that is, they are older) than Seyfert galaxies. Quasars are detected without observing the underlying galaxies, whereas Seyfert galaxies are detected both by the energetic core and by the entire galaxy radiation.