and process the data. The catalog was published between 1918 and 1924. Following the death of Pickering (1919), Cannon took control of the projects. An extension to the original works was published between 1925 and 1936, where over 46,850 stars were classified.

In the later years of the program, following the publication of the catalog, several women joined and continued to make contributions. Margaret Walton Mayall contributed to the classification of stellar spectra. She later went on to lead