The American Astronomical Society has about 6500 members as of 1995, and world wide there are probably more than 15,000. The 1994 issue of the Astronomy and Astrophysics Abstracts lists over 15,000 authors for papers published during the 10 month period from January to October in the american and international astronomy journals. If you figure that probably 1/4 of these are graduate students and not matured astronomers with PhDs, then you get about 12,000 actively publishing astronomers during this 10 month period, and something like 12,000 X 12/10 = 14,000 active astronomers world wide that publish each year or so. This is not a very large group compared to the over 100,000+ physicists worldwide and many times that number of scientists in biological + physical sciences which I imagine number close to 1 million.