The MK Spectral classification system was founded by W.W. Morgan
and P.C. Keenan in the year 1943, with the publication of the
first photographic spectral classification atlas, An Atlas of
Stellar Spectra (Morgan, Keenan & Kellman 1943). Since that
time, the MK system has been extensively revised and refined by
Morgan, Keenan and others. In the late 1970's, two important
spectral atlases, summarizing the development of the MK system
up until that time, were published. These atlases, the Revised
MK Spectral Atlas for Stars Earlier than the Sun by Morgan, Abt
& Tapscott (1978) and An Atlas of Spectra of the Cooler Stars:
Types G,K,M,S and C, by Keenan & McNeil (1976), are the
inspiration for this new digital spectral classification atlas.
Indeed, some of the pages in this atlas are "digitized" versions
of pages from those two atlases. The MK spectral classification
system is a natural, empirical system of spectral classification
which uses in the classification process only the directly
observable features in t