Columbia subject headings:
Active galaxies--Congresses.
Astrophysics--Congresses.
Quasars--Congresses.
Harvard subject headings:
Galaxies--Congresses
Osterbrock, Donald E.
Quasars--Congresses
Princeton subject headings:
Astrophysics--Congresses.
Galactic nuclei--Congresses.
Quasars--Congresses.