  The number of astronomers for a country registered to the IAU is known to
have a correlation with the GDP. However, the robustness of this relationship
can be doubted, because the fraction of astronomers joining the IAU differs
from country to country. Here we revisit this correlation by using the recent
data updated as of 2017, and then we find a similar correlation by using the
total enumeration of astronomers and astrophysicists with PhD degrees and
working in each country, instead of adopting the number of IAU members. We
confirm the existence of two subgroup in the correlation. One group consists of
European advanced countries having long history of modern astronomy, while the
other group consists of countries having experienced recent rapid economic
development. In order to find causation in the correlation, we obtain the
long-term variations of the number of astronomers, population, and the GDP for
a number of countries to find that the number of astronomers per citizen for
recently developing countries has increased more rapidly as GDP per capita
increased, than that for fully developed countries. We collect a demographic
data of the Korean astronomical community. From these findings we estimate the
proper size of the Korean astronomical community by considering the society's
economic power and population. The current number of PhD astronomers working in
Korea is approximately 310, but it should be 550 that is large enough to be
comparable and competitive to the sizes of Spainish, Canadian, and Japanese
astronomical communities. We discuss on the way how to overcome the
vulnerability of the Korean astronomical community, based on the statistics of
national R&D expenditure structure comparing with that of other major advanced
countries.
