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Seventy-five years ago the first three volumes of The Henry Draper Catalogue were published. The pages printed in 1918 contain the spectral types, revised magnitudes, and updated positions for more than 77,000 stars. For the nine volumes of the catalogue, Cannon classified spectra for 225,300 stars; and in her lifetime, spectra for almost 400,000 stars. This work netted her half a dozen honorary degrees, the Draper Medal of the NAS, and numerous other prizes and honors.
In his preface to Volume 1, Edward Pickering noted that it took two years to process the copy for the initial volumes and estimated that it would take two more years to complete the copy for the remaining volumes. But shortly after he wrote the preface for Volume 3 in December 1918, Pickering died. And it proved to take three times as long as he had predicted to complete the publication of all nine volumes of the catalogue by the spring of 1924.
Although Cannon had enjoyed much more independence and status than the other women at HCO, she had looked to Pickering for guidance and financial support for her astronomical projects. Without him, she had to develop other resources and also had to represent the Harvard Classification for the first IAU meeting in Rome in 1922. Although she did not attend the meeting, she corresponded with Frederick Seares at Mount Wilson Observatory about various questions that astronomers had raised about classifying spectra.
Meanwhile, in 1921 Harlow Shapley was appointed Director of HCO. He oversaw the publication of the final volumes of the HD and encouraged Cannon to extend it for stars in special regions. For the HD Extension, he hired Margaret Walton to assist Cannon. But the cost of labor to determine positions and magnitudes was prohibitive, so for many stars the HDE lists only the BD number and spectral type. Even that format proved too costly in the depression and war years. Consequently, the last volume of the HDE was published as charts after World War II.
