An early attempt to classify the spectra of stars, developed by P. A. Secchi in the 1860s. Secchi grouped stellar spectra into five types, on the basis of direct visual observation. Type I was the equivalent of today's spectral types B and A; Type II encompassed F, G, and K stars; Type III was the equivalent of the M stars; Type IV encompassed carbon stars (Harvard types R, N); and the rare Type V described spectra with unusual bright lines, such as from Wolf–Rayet stars and planetary nebulae. Secchi's scheme was superseded by the photographic Harvard classification system.
Subjects: Astronomy and Astrophysics.