Honorary Membership was limited to 10 from 1890-1900, and to 15 from 1901 onwards. Corresponding Membership was a lesser class of Honoris causa membership in the early years. A few honorary members, such as Barnard, were first made corresponding members for a short time before being recommissioned as honorary members.
| Nation(s) | Start | End | |
|---|---|---|---|
| Shearmen, Mr. T.S.H. | Canada | 1890 | 1900 |
| Shapley, Dr. Harlow | USA | 1947 | 1972 |
| Schwarzschild, Dr. Martin | USA | 1963 | 1999 |
| Schlesinger, Dr. Frank | USA | 1916 | 1943 |
| Sandage, Dr. Allan R. | USA | 1975 | 2010 |
| Ryle, Sir Martin | United Kingdom | 1973 | 1983 |
| Russell, Prof. Henry Norris | USA | 1946 | 1957 |
| Russell, Rev. Norman H. | Canada/India | 1898 | 1902 |
| Rogers, Prof. William A. | USA | 1894 | 1898 |
| Robinson, Mr. Leif J. | USA | 2000 | 2011 |