Editing Stellar classification (section)

===The current Harvard system (1912)===
In 1901, [[Annie Jump Cannon]] returned to the lettered types, but dropped all letters except O, B, A, F, G, K, M, and N<!--class N now absorbed into class C --> used in that order, as well as P for planetary nebulae and Q for some peculiar spectra. She also used types such as B5A for stars halfway between types B and A, F2G for stars one fifth of the way from F to G, and so on.<ref>{{cite journal |last1=Cannon |first1=Annie J. |last2=Pickering |first2=Edward C. |year=1901 |title=Spectra of bright southern stars photographed with the 13&nbsp;inch Boyden telescope as part of the Henry Draper Memorial |journal=Annals of Harvard College Observatory |volume=28 |pages=129 |bibcode=1901AnHar..28..129C}}</ref><ref>Hearnshaw (1986) pp.&nbsp;117–119,</ref>

Finally, by 1912, Cannon had changed the types B, A, B5A, F2G, etc. to B0, A0, B5, F2, etc.<ref>{{cite journal |last1=Cannon |first1=Annie Jump |last2=Pickering |first2=Edward Charles |year=1912 |title=Classification of 1,688&nbsp;southern stars by means of their spectra |journal=Annals of the Astronomical Observatory of Harvard College |volume=56 |issue=5 |pages=115 |bibcode=1912AnHar..56..115C}}</ref><ref>Hearnshaw (1986) pp. 121–122</ref> This is essentially the modern form of the Harvard classification system. This system was developed through the analysis of spectra on photographic plates, which could convert light emanated from stars into a readable spectrum.<ref>{{cite web |title=Annie Jump Cannon |website=www.projectcontinua.org |language=en-US |url=http://www.projectcontinua.org/annie-jump-cannon/ |access-date=2020-06-10}}</ref>