<P> In the 1880s, the astronomer Edward C. Pickering began to make a survey of stellar spectra at the Harvard College Observatory, using the objective - prism method . A first result of this work was the Draper Catalogue of Stellar Spectra, published in 1890 . Williamina Fleming classified most of the spectra in this catalogue . </P> <P> The catalogue used a scheme in which the previously used Secchi classes (I to IV) were subdivided into more specific classes, given letters from A to N. Also, the letters O, P, and Q were used--O for stars whose spectra consisted mainly of bright lines, P for planetary nebulae, and Q for stars not fitting into any other class . </P> <P> In 1897, another worker at Harvard, Antonia Maury, placed the Orion subtype of Secchi class I ahead of the remainder of Secchi class I, thus placing the modern type B ahead of the modern type A. She was the first to do so, although she did not use lettered spectral types, but rather a series of twenty - two types numbered from I to XXII . </P> <P> In 1901, Annie Jump Cannon returned to the lettered types, but dropped all letters except O, B, A, F, G, K, and M, 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 . Finally, by 1912, Cannon had changed the types B, A, B5A, F2G, etc. to B0, A0, B5, F2, etc . This is essentially the modern form of the Harvard classification system . </P>

When was the sun classified as a star