Editing Stellar classification (section)

===Secchi classes===
During the 1860s and 1870s, pioneering stellar spectroscopist [[Angelo Secchi]] created the ''Secchi classes'' in order to classify observed spectra. By 1866, he had developed three classes of stellar spectra, shown in the table below.<ref>[http://gallica.bnf.fr/ark:/12148/bpt6k30204/f364.table Analyse spectrale de la lumière de quelques étoiles, et nouvelles observations sur les taches solaires], P. Secchi, ''Comptes Rendus des Séances de l'Académie des Sciences'' '''63''' (July–December 1866), pp. 364–368.</ref><ref>[http://gallica.bnf.fr/ark:/12148/bpt6k30204/f623.table Nouvelles recherches sur l'analyse spectrale de la lumière des étoiles], P. Secchi, ''Comptes Rendus des Séances de l'Académie des Sciences'' '''63''' (July–December 1866), pp. 621–628.</ref><ref>{{cite book |last=Hearnshaw |first=J. B. |date=1986 |title=The Analysis of Starlight: One Hundred and Fifty Years of Astronomical Spectroscopy |location=Cambridge, UK |publisher=Cambridge University Press |pages=60, 134 |isbn=978-0-521-25548-6}}</ref>

In the late 1890s, this classification began to be superseded by the Harvard classification, which is discussed in the remainder of this article.<ref>{{cite web| url = http://www.astro.ufl.edu/~gott/AST1002/Additional_Notes/Add_notes.week5| title = Classification of Stellar Spectra: Some History}}</ref><ref>{{cite book |last=Kaler |first=James B. |date=1997 |title=Stars and Their Spectra: An Introduction to the Spectral Sequence |location=Cambridge |publisher=Cambridge University Press |pages=[https://archive.org/details/starstheirspectr0000kale/page/62 62–63] |isbn=978-0-521-58570-5 |url=https://archive.org/details/starstheirspectr0000kale/page/62 }}</ref><ref>p. 60–63, Hearnshaw 1986; pp. 623–625, Secchi 1866.</ref>

{| class="wikitable"
|-
! Class&nbsp;number !! Secchi&nbsp;class&nbsp;description
|-
| Secchi class&nbsp;I || White and blue stars with broad heavy [[hydrogen line]]s, such as [[Vega]] and [[Altair]]. This includes the modern class&nbsp;A and early class&nbsp;F.
|-
| Secchi class&nbsp;I<br />(Orion&nbsp;subtype) || A subtype of Secchi class&nbsp;I with narrow lines in place of wide bands, such as [[Rigel]] and [[Bellatrix]]. In modern terms, this corresponds to early B-type stars
|-
| Secchi class&nbsp;II || Yellow stars – hydrogen less strong, but evident metallic lines, such as the [[Sun]], [[Arcturus]], and [[Capella]]. This includes the modern classes G and K as well as late class&nbsp;F.
|-
| Secchi class&nbsp;III || Orange to red stars with complex band spectra, such as [[Betelgeuse]] and [[Antares]].<br />This corresponds to the modern class&nbsp;M.
|-
| Secchi class&nbsp;IV || In 1868, he discovered [[carbon star]]s, which he put into a distinct group:<ref>pp. 62–63, Hearnshaw 1986.</ref><br />Red stars with significant [[carbon]] bands and lines, corresponding to modern classes C and S.
|-
| Secchi class&nbsp;V || In 1877, he added a fifth class:<ref>p. 60, Hearnshaw 1986.</ref><br />[[Emission-line]] stars, such as [[Gamma Cassiopeiae]] and [[Beta Lyrae|Sheliak]], which are in modern class&nbsp;Be. In 1891, Edward Charles Pickering proposed that class V should correspond to the modern class O (which then included [[Wolf–Rayet star]]s) and stars within planetary nebulae.<ref>''Catchers of the Light: The Forgotten Lives of the Men and Women Who First Photographed the Heavens'' by Stefan Hughes.</ref>
|}

The [[Roman numerals]] used for Secchi classes should not be confused with the completely unrelated Roman numerals used for Yerkes luminosity classes and the proposed neutron star classes.