Columbia subject headings:
Galactic center--Congresses.
Interstellar matter--Congresses.
Milky Way--Congresses.
Harvard subject headings:
Galactic center--Congresses.
Interstellar matter--Congresses.
Milky Way--Congresses.
Princeton subject headings:
Galactic center--Congresses.
Galaxies--Congresses.
Interstellar matter--Congresses.
Milky Way--Congresses.