Harvard Spectral Classification System

Harvard improved and extended spectroscopic sequence

In this system the stars are arranged in a sequence according to the general appearance of their spectra. The fundamental parameter in the sequence is the ionization temperature in stellar atmosphere. The temperature decreases from O to M and a stars become redder from O to M. The subdivisions through spectral classes are given as decimal ( e.g. O5, O6, O7, O8, O9, B0, B1, ......... ). The original use of capital letters, introduced by Pickering, was complemented by miss Cannon providing, finally, the order shown in the following figure.

Peculiarities not supported by the spectroscopic sequence classification criteria

Some images of spectral sequences

© 2006 - Valter Arnò.