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 | |
|---|---|---|---|
| Monck, Prof. William Henry Stanley | Ireland | 1898 | 1915 |
| Moore, Sir Patrick | United Kingdom | 1993 | 2013 |
| Morrison, Dr. Joseph | Canada/USA | 1891 | 1898 |
| Newcomb, Rear Admiral Dr. Simon | USA | 1891 | 1909 |
| Newnham, Right Rev. Jervois Arthur | United Kingdom/Canada | 1895 | 1905 |
| Oort, Dr. Jan Hendrik | Netherlands | 1954 | 1992 |
| Pasachoff, Dr. Jay M. | USA | 2003 | 2022 |
| Peal, Mr. Samuel Edward | United Kingdom/India | 1891 | 1897 |
| Pettit, Mr. H. | Canada | 1890 | 1890 |
| Pickering, Dr. Edward Charles, OPM | USA | 1894 | 1919 |