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The stellar classification used to classify stars by color or temperature has seven main classes and four other ones. It is called the '''Morgan-Keenan''' stellar classification. It was originally proposed by {{flags|it}} Italian astronomer Angelo Secchi, but has been improved by {{flags|uk}} Harvard professors William Morgan and Philip Keenan.
 
The stellar classification used to classify stars by color or temperature has seven main classes and four other ones. It is called the '''Morgan-Keenan''' stellar classification. It was originally proposed by {{flags|it}} Italian astronomer Angelo Secchi, but has been improved by {{flags|uk}} Harvard professors William Morgan and Philip Keenan.
  
The Harvard Computers were a group of women astronomers best known for their contributions to the modern classes for stars. The most prominent of them were Annie Jump Cannon, who dropped all unnecessary letters from the larger Draper system leaving it as "O, B, A, F, G, K, M", and Williamina Fleming, who classified most of the stars in the Draper system.
+
There are stellar classes '''P''' and '''Q''', which are used for planetary nebulae and novae and pulsars respectively.
 
 
Jump Cannon left stellar classes '''P''' and '''Q''', which are used for planetary nebulae and novae and pulsars respectively.
 
 
 
It was originally thought that for stellar classes G to M there was a significant difference in dwarfs and giants, in terms of size and temperature, and being beyond distinguishable for earlier stellar classes. However, with the discovery of subdwarf O and B stars, this has proved to apply to classes O and B as well. White dwarfs are the dwarf counterparts of classes A and F in terms of average temperature, though they now belong to an entirely different class (D).
 
 
 
"Late-type" stars refer to classes F, G, K, and M, and the cooler subclasses of any class (such as G5-G9). "Early-type" refers to classes O, B, and A and the hotter subclases of any class. Thus "early" means hotter, and "late" means cooler. These terms were derived from an obsolete model of stellar evolution based on the [[Kelvin-Helmholtz mechanism]], where stars started as red giants, before contracting into blue main-sequence stars and finally into red dwarfs. This model was rendered obsolete by the discovery that stars are powered by nuclear fusion. However, the terms "early" and "late", based on the model's timescale, were carried on, beyond the demise of the theory on which they were based.
 
 
{| class="wikitable"
 
{| class="wikitable"
 
|-
 
|-
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|}
 
|}
 
{| class="wikitable article-table"
 
{| class="wikitable article-table"
! colspan="2" |Stellar Class
+
!Stellar Class
 
 
 
* (examples)
 
* (examples)
 
!Secchi's original classification<ref>ISBN 0-521-25548-1</ref><ref>http://gallica.bnf.fr/ark:/12148/bpt6k30204/f623.table</ref><ref>http://gallica.bnf.fr/ark:/12148/bpt6k30204/f364.table</ref><ref>pp. 62–63, Hearnshaw 1986.</ref><ref>p. 60, Hearnshaw 1986.</ref>
 
!Secchi's original classification<ref>ISBN 0-521-25548-1</ref><ref>http://gallica.bnf.fr/ark:/12148/bpt6k30204/f623.table</ref><ref>http://gallica.bnf.fr/ark:/12148/bpt6k30204/f364.table</ref><ref>pp. 62–63, Hearnshaw 1986.</ref><ref>p. 60, Hearnshaw 1986.</ref>
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(in Kelvin)
 
(in Kelvin)
 
!Percentage (%) of known stars
 
!Percentage (%) of known stars
!Relevant image
+
!Possible color appearance
 
|-
 
|-
| rowspan="4" |Early-type
 
 
|'''[[Luminous Blue Variables|LBV]]'''[[Luminous Blue Variables| (luminous blue variable)]]
 
|'''[[Luminous Blue Variables|LBV]]'''[[Luminous Blue Variables| (luminous blue variable)]]
 
* [[Pistol Star]]
 
* [[Pistol Star]]
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|7,500 to 50,000
 
|7,500 to 50,000
 
| rowspan="2" |0.000033
 
| rowspan="2" |0.000033
| rowspan="2" |[[File:O5v-spectre.png|thumb|Spectrum of an O5V star]]
+
| rowspan="2" |[[File:Etoile du pistolet.png|278x278px]]
 
|-
 
|-
 
|'''O'''
 
|'''O'''
*[[Alnitak]]
+
* Stars of [[Orion's belt|Orion's Belt]]
 
|'''O'''
 
|'''O'''
|30,000 to 50,000 (giants) 40,000 to 100,000 (dwarfs)
+
|30,000 to 50,000
 
|-
 
|-
 
|'''B'''
 
|'''B'''
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|'''I (Orion subtype), V (Be stars)'''
 
|'''I (Orion subtype), V (Be stars)'''
 
|'''B'''
 
|'''B'''
|10,000 to 30,000 (giants)
+
|10,000 to 30,000
20,000 to 40,000 (dwarfs)
 
<br />
 
 
|0.13
 
|0.13
|[[File:A Snapshot of the Jewel Box cluster with the ESO VLT.jpg|257x257px]]
+
|[[File:Rigel blue supergiant.jpg|278x278px]]
 
|-
 
|-
 
|'''A'''
 
|'''A'''
*[[Sirius A]]
+
* [[Vega]]
 
| rowspan="2" |'''I'''
 
| rowspan="2" |'''I'''
 
|'''A, C, D'''
 
|'''A, C, D'''
|7,500 to 10,000 (giants)
+
|7,500 to 10,000
3,000 to 250,000 (dwarfs; see below)
 
 
|0.7
 
|0.7
|[[File:Size Vega.png|260x260px]]
+
|[[File:Debris Disk Around Vega.jpg|frameless|260x260px]]
 
|-
 
|-
| rowspan="3" |
 
 
|'''F'''
 
|'''F'''
*[[Polaris]]
+
* Procyon
 
|'''E, F'''
 
|'''E, F'''
|6,000 to 7,500 (giants)
+
|6,000 to 7,500
3,000 to 250,000 (dwarfs; see below)
 
 
|3
 
|3
|[[File:Polaris alpha ursae minoris.jpg|263x263px]]
+
|[[File:Procyon Celestia.jpg|272x272px]]
 
|-
 
|-
 
|'''G'''
 
|'''G'''
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| rowspan="2" |'''II'''
 
| rowspan="2" |'''II'''
 
|'''G, H, I'''
 
|'''G, H, I'''
|5,000 to 6,000 (giants)
+
|5,000 to 6,000
5,700 to 6,400 (dwarfs)
 
 
|7
 
|7
|[[File:Sun920607.jpg|258x258px]]
+
|[[File:Alpha Centauri relative sizes.svg|thumb|Comparison of the sizes and colors of the stars in the [[Alpha Centauri]] system with the Sun.]]
 
|-
 
|-
 
|'''K'''
 
|'''K'''
*[[Arcturus]]
+
* [[Alpha Centauri]] B
 
|'''K, L'''
 
|'''K, L'''
|4,000 to 5,000 (giants)
+
|4,000 to 5,000
4,800 to 5,500 (dwarfs)
 
 
|12.1
 
|12.1
|[[File:Redgiants.svg|237x237px]]
+
|[[File:Iota-draconis-b.jpg|280x280px]]
 
|-
 
|-
| rowspan="5" |Late-type
 
 
|'''M'''
 
|'''M'''
 
* [[Betelgeuse]]
 
* [[Betelgeuse]]
 
|'''III'''
 
|'''III'''
 
|'''M'''
 
|'''M'''
|2,000 to 4,000 (giants)
+
|2,400 to 4,000
3,400 to 4,000 (dwarfs)
 
 
|77
 
|77
|[[File:VY Canis Hypergiant.jpg|alt=|left|thumb|282x282px|[[VY Canis Majoris]]]]
+
|[[File:Antares - Eso1726a.tif|left|thumb|[[Antares]]]]
|-
 
|'''R'''
 
* S Camelopardalis
 
| rowspan="3" |'''IV'''
 
| rowspan="3" |'''N'''
 
|3,000 to 5,000
 
| rowspan="3" |unknown
 
|[[File:IRAS 06088+1909 (2MASS).jpg|321x321px]]
 
|-
 
|'''N'''
 
* Y Canum Venaticorum
 
| rowspan="2" |4,000 to 2,000
 
|[[File:Curious spiral spotted by ALMA around red giant star R Sculptoris (data visualisation).jpg|250x250px]]
 
|-
 
|'''S'''
 
* Chi Cygni
 
|[[File:Red Giant Chi Cygni.png|280x280px]]
 
 
|-
 
|-
 
|[[File:Relative star sizes.svg|thumb|249x249px|Objects included are the Sun, the red and brown dwarf companions of Gliese 229, Teide 1 and [[Jupiter]].]]'''[[Brown dwarf|Brown Dwarfs]]''' are stellar objects that cannot fuse [[hydrogen]] with their interiors, and thus can only radiate in infrared light. The first such object discovered was '''Teide 1,''' located in the constellation Taurus.
 
|[[File:Relative star sizes.svg|thumb|249x249px|Objects included are the Sun, the red and brown dwarf companions of Gliese 229, Teide 1 and [[Jupiter]].]]'''[[Brown dwarf|Brown Dwarfs]]''' are stellar objects that cannot fuse [[hydrogen]] with their interiors, and thus can only radiate in infrared light. The first such object discovered was '''Teide 1,''' located in the constellation Taurus.
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|[[File:Bds-001.jpg|thumb|220x220px|Comparison between the three types of brown dwarfs.|left]]
 
|[[File:Bds-001.jpg|thumb|220x220px|Comparison between the three types of brown dwarfs.|left]]
 
|-
 
|-
| rowspan="3" |Early-type
+
|'''S'''
 +
* W Aquilae
 +
| rowspan="2" |'''IV'''
 +
| rowspan="2" |'''N'''
 +
| rowspan="2" |1,000 to 3,000
 +
| rowspan="2" |unknown
 +
|[[File:W Aquilae binary cropped.jpg|left|thumb|245x245px|W Aquilae]]
 +
|-
 +
|'''Carbon Stars'''
 +
*'''R'''
 +
*'''N'''
 +
|[[File:Curious spiral spotted by ALMA around red giant star R Sculptoris (data visualisation).jpg|253x253px]]
 +
|-
 
|'''Wolf-Rayet Stars'''
 
|'''Wolf-Rayet Stars'''
 
*[[Gamma Velorum]]
 
*[[Gamma Velorum]]
| rowspan="3" |'''V''' (according to Edward Charles Pickering)
+
| rowspan="2" |'''V''' (according to Edward Charles Pickering)
 
|'''O'''
 
|'''O'''
 
(later separated from O-type stars)
 
(later separated from O-type stars)
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|unknown
 
|unknown
 
|[[File:R136a1.jpg|253x253px]]
 
|[[File:R136a1.jpg|253x253px]]
|-
 
|'''D'''
 
* [[Sirius B]]
 
|'''A, D?'''
 
|3,000 to 250,000
 
|''common''
 
|[[File:Sirius A and B Hubble photo.jpg|240x240px]]
 
 
|-
 
|-
 
|'''P'''
 
|'''P'''
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|[[File:Heart and Soul nebulae.jpg|left|thumb|262x262px|The "Heart and Soul nebulae"]]
 
|[[File:Heart and Soul nebulae.jpg|left|thumb|262x262px|The "Heart and Soul nebulae"]]
 
|-
 
|-
|?
 
 
|'''Q'''
 
|'''Q'''
 
* DN Geminorum
 
* DN Geminorum

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