percent of physics, even though 13 percent of the combined physics and astronomy Ph.D.s produced are in astronomy and astrophysics.) Astronomy remains arguably the most vibrant of the physical sciences in the United States.
To gain further insight into the trends in the number of astronomers, the committee estimated the fraction of astronomers by discipline (typically by wavelength orientation) and also by scientific field (e.g., planet formation, stellar astronomy, instrumentation) from the AAS membership lists. This was done for two years, 1989 and 1997, before and after the 1991 Decadal Survey. In both cases, random samples of 600 to 700 full, U.S. members were drawn from the AAS rolls. U.S. AAS membership refers to residency in the United States and its territories and commonwealths (e.g., Guam, Puerto Rico).
Individuals were classified by discipline, field, and place of employment. The classifications employ a fairly simple mnemonic: OO - observational optical, OR - observational radio, and so forth. The full lists of classification categories are given in Table A.1 in Appendix A. These same categorizations were used for the classification of publications and funding sources discussed below in Section 4.2. The committee is aware that many individuals fall into more than one of the categorizations and that because only about 20 percent of the U.S. full AAS membership was sampled, the accuracy of the estimates for distribution by discipline and field is necessarily limited. Nonetheless, such categorizations are useful.