Henry Draper Extension

The Henry Draper Extension is a continuation of the Henry Draper Catalogue, a significant astronomical compilation. The original catalogue, named in honor of American astronomer Henry Draper, was compiled at Harvard College Observatory. It began the modern system of classifying stars by their spectral types.

The Henry Draper Catalogue (HD) initially listed the positions, magnitudes, and spectral types of over 225,000 stars. The Henry Draper Extension (HDE) was published in several parts between 1925 and 1949, adding the spectral data for an additional 133,782 stars. These extensions significantly expanded the comprehensive data available for stellar classification and astronomical research.12