Editing Star (section)

==Classification==
{{Main|Stellar classification}}
{| class="wikitable" style="float: right; text-align: center; margin-left: 1em;"
|+ Surface temperature ranges for<br />different stellar classes<ref>{{cite web
 | last=Smith | first=Gene | date=1999-04-16
 | url=http://casswww.ucsd.edu/public/tutorial/Stars.html
 | title=Stellar Spectra
 | publisher=University of California, San Diego
 | access-date=2006-10-12}}</ref>
! Class
! Temperature
! Sample star
|- style="background: {{star-color|O}}"
| O
| 33,000&nbsp;K&nbsp;or&nbsp;more
| [[Zeta Ophiuchi]]
|- style="background: {{star-color|B}}"
| B
| 10,500–30,000&nbsp;K
| [[Rigel]]
|- style="background: {{star-color|A}}"
| A
| 7,500–10,000&nbsp;K
| [[Altair]]
|- style="background: {{star-color|F}}"
| F
| 6,000–7,200&nbsp;K
| [[Procyon|Procyon&nbsp;A]]
|- style="background: {{star-color|G}}"
| G
| 5,500–6,000&nbsp;K
| [[Sun]]
|- style="background: {{star-color|K}}"
| K
| 4,000–5,250&nbsp;K
| [[Epsilon Indi]]
|- style="background: {{star-color|M}}"
| M
| 2,600–3,850&nbsp;K
| [[Proxima Centauri]]
|}

The current stellar classification system originated in the early 20th century, when stars were classified from ''A'' to ''Q'' based on the strength of the [[hydrogen line]].<ref>{{cite journal
 | last=Fowler | first=A.
 | title=The Draper Catalogue of Stellar Spectra
 | journal=Nature
 | date=April 1891 | volume=45 | issue=1166 | pages=427–428 | doi= 10.1038/045427a0 |bibcode= 1892Natur..45..427F| doi-access=free }}</ref> It was thought that the hydrogen line strength was a simple linear function of temperature. Instead, it was more complicated: it strengthened with increasing temperature, peaked near 9000&nbsp;K, and then declined at greater temperatures. The classifications were since reordered by temperature, on which the modern scheme is based.<ref name=carlos>{{cite book
 | first1=Carlos | last1=Jaschek | last2=Jaschek | first2=Mercedes
 | date=1990 | title=The Classification of Stars
 | publisher=Cambridge University Press | pages=31–48
 | isbn=978-0-521-38996-9}}</ref>

Stars are given a single-letter classification according to their spectra, ranging from type ''O'', which are very hot, to ''M'', which are so cool that molecules may form in their atmospheres. The main classifications in order of decreasing surface temperature are: ''O, B, A, F, G, K'', and ''M''. A variety of rare spectral types are given special classifications. The most common of these are types ''L'' and ''T'', which classify the coldest low-mass stars and brown dwarfs. Each letter has 10 sub-divisions, numbered from 0 to 9, in order of decreasing temperature. However, this system breaks down at extreme high temperatures as classes ''O0'' and ''O1'' may not exist.<ref name="spectrum">{{cite web
 | first=Alan M
 | last=MacRobert
 | url=http://www.skyandtelescope.com/howto/basics/3305876.html
 | title=The Spectral Types of Stars
 | publisher=Sky and Telescope
 | access-date=2006-07-19
 | archive-date=2013-10-22
 | archive-url=https://web.archive.org/web/20131022124237/http://www.skyandtelescope.com/howto/basics/3305876.html
 | url-status=dead
 }}</ref>

In addition, stars may be classified by the luminosity effects found in their spectral lines, which correspond to their spatial size and is determined by their surface gravity. These range from ''0'' ([[hypergiant]]s) through ''III'' ([[giant star|giants]]) to ''V'' (main sequence dwarfs); some authors add ''VII'' (white dwarfs). Main sequence stars fall along a narrow, diagonal band when graphed according to their absolute magnitude and spectral type.<ref name="spectrum" /> The Sun is a main sequence ''G2V'' yellow dwarf of intermediate temperature and ordinary size.<ref name="RixHay2015">{{cite book |last1=Rix |first1=Erika |url=https://books.google.com/books?id=7pCKCgAAQBAJ&pg=PA43 |title=Solar Sketching: A Comprehensive Guide to Drawing the Sun |last2=Hay |first2=Kim |last3=Russell |first3=Sally |last4=Handy |first4=Richard |date=2015 |publisher=Springer |isbn=978-1-4939-2901-6 |page=43}}</ref>

There is additional nomenclature in the form of lower-case letters added to the end of the spectral type to indicate peculiar features of the spectrum. For example, an "''e''" can indicate the presence of emission lines; "''m''" represents unusually strong levels of metals, and "''var''" can mean variations in the spectral type.<ref name="spectrum" />

White dwarf stars have their own class that begins with the letter ''D''. This is further sub-divided into the classes ''DA'', ''DB'', ''DC'', ''DO'', ''DZ'', and ''DQ'', depending on the types of prominent lines found in the spectrum. This is followed by a numerical value that indicates the temperature.<ref>{{cite web
 | url= http://www.physics.uq.edu.au/people/ross/ph3080/whitey.htm
 | archive-url= https://web.archive.org/web/20091008115925/http://www.physics.uq.edu.au/people/ross/ph3080/whitey.htm
 | archive-date= 2009-10-08
 | title= White Dwarf (wd) Stars
 | publisher= White Dwarf Research Corporation
 | access-date= 2006-07-19}}</ref>