Columbia subject headings:
Comets--Congresses.
Interstellar matter--Congresses.
Stars--Formation--Congresses.
Harvard subject headings:
Comets--Congresses
Interstellar matter--Congresses.
Stars--Formation--Congresses
Princeton subject headings:
Comets--Congresses.
Interstellar matter--Congresses.
Stars--Formation--Congresses.