Book: Draper Catalogue of Stellar Spectra

Overview

The Draper Catalogue of Stellar Spectra, compiled under the direction of Annie Jump Cannon and published by the Harvard College Observatory in the early 20th century, is a monumental census of stellar spectral types. Presented as the Henry Draper Catalogue (commonly shortened to HD or the Draper Catalogue), it assigns spectral classifications to more than 225, 000 stars based on photographic spectra taken at Harvard. The catalog established a practical, uniform system for recording the dominant spectral characteristics of stars across the sky.

Contents and Format

Entries in the catalogue provide each star's Henry Draper number, position, and spectral classification derived from objective-prism and slitless photographic plates. The work aggregates thousands of measurements into a single, searchable reference that spans bright and faint stars across both hemispheres. Many entries include subtype distinctions and notes when spectra were peculiar, composite, or otherwise noteworthy, making the catalogue useful for both identification and scientific study.

Classification Method

Annie Jump Cannon refined and systematized the spectral classification into the sequence still familiar today: O, B, A, F, G, K, M, with finer numeric subdivisions used to indicate gradations between types. Her approach emphasized consistent, reproducible criteria so that different observers could assign compatible types. The classifications were made by visually inspecting photographic spectra and applying a set of empirical rules developed at Harvard, yielding a practical taxonomy tied closely to stellar temperature and spectral line behavior.

Scientific Impact

The Draper Catalogue transformed stellar astronomy from sparse, qualitative descriptions into a quantitative, population-level science. By providing a uniform spectral inventory for hundreds of thousands of stars, it enabled statistical studies of stellar temperatures, distributions, and the relationships between spectra and luminosity. The catalog's widespread adoption anchored subsequent work in stellar classification, stellar evolution, and galactic structure, and it served as a foundational dataset for later photometric and spectroscopic surveys.

Legacy and Usage

Henry Draper (HD) numbers remain a standard way to refer to stars in astronomical literature and catalog cross-references, reflecting the catalogue's lasting practical value. The methods and conventions refined by Cannon at Harvard influenced later classification schemes, including those that introduced luminosity classes and more detailed spectral diagnostics. The Draper Catalogue also stands as a landmark in the history of women in science, showcasing both the scale of systematic astronomical work at Harvard and the central role played by Annie Jump Cannon and her colleagues in building modern stellar astronomy.