The Oxford Biblical Studies Online and Oxford Islamic Studies Online have retired. Content you previously purchased on Oxford Biblical Studies Online or Oxford Islamic Studies Online has now moved to Oxford Reference, Oxford Handbooks Online, Oxford Scholarship Online, or What Everyone Needs to Know®. For information on how to continue to view articles visit the subscriber services page.

Related Content

Related Overviews


More Like This

Show all results sharing these subjects:

  • Science and technology
  • Astronomy and Cosmology


Show Summary Details


Harvard classification

Quick Reference

A system of classifying stars according to the characteristics of their spectra, introduced at Harvard College Observatory in 1890 by E. C. Pickering, which culminated in the *Henry Draper Catalogue. At first, stars were ordered according to the strength of their hydrogen absorption lines (the Balmer series), from A (strongest) to P. Eventually several letters were merged or dropped, and the remaining spectral types were rearranged into the sequence O, B, A, F, G, K, M, in order of decreasing surface temperature. Early in the 20th century, spectral types R and N were applied to carbon-rich versions of types G, K, and M (now known as carbon stars), and type S (M stars with heavy-metal lines) was subsequently added (see s star). The Harvard system has since been superseded by the Morgan–Keenan classification system. See also spectral classification.

Reference entries