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margin: .1em .5em;"><b>[<span class="plainlinks plainlinksneverexpand"><a rel="nofollow" class="external text" href="https://citizendium.org/wiki/index.php?title=Stellar_classification_(astrophysics)&action=edit&section=0"><font size="2">edit intro</font></a></span>]</b></div> </td></tr></tbody></table></div> <p><b>Stellar classification</b> is the categorization of <a href="/wiki/Star" title="Star">stars</a> by various properties. A common classification is surface temperature. Beginning with early <a href="/wiki/Electromagnetic_spectrum" title="Electromagnetic spectrum">spectral</a> schema<sup id="cite_ref-1" class="reference"><a href="#cite_note-1">[1]</a></sup> in the 19th century ranking stars from A to P, the spectral classification, called “Morgan-Keenan spectral classification” <sup id="cite_ref-2" class="reference"><a href="#cite_note-2">[2]</a></sup><sup id="cite_ref-3" class="reference"><a href="#cite_note-3">[3]</a></sup> now ranks stars in seven main types: O, B, A, F, G, K, M.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4">[4]</a></sup> Each spectral classification is further divided into tenths. Our sun, Sol, is a G2. </p> <div id="toc" class="toc" role="navigation" aria-labelledby="mw-toc-heading"><input type="checkbox" role="button" id="toctogglecheckbox" class="toctogglecheckbox" style="display:none" /><div class="toctitle" lang="en" dir="ltr"><h2 id="mw-toc-heading">Contents</h2><span class="toctogglespan"><label class="toctogglelabel" for="toctogglecheckbox"></label></span></div> <ul> <li class="toclevel-1 tocsection-1"><a href="#History"><span class="tocnumber">1</span> <span class="toctext">History</span></a></li> <li class="toclevel-1 tocsection-2"><a href="#Classification_system"><span class="tocnumber">2</span> <span class="toctext">Classification system</span></a></li> <li class="toclevel-1 tocsection-3"><a href="#Luminosity_classes"><span class="tocnumber">3</span> <span class="toctext">Luminosity classes</span></a></li> <li class="toclevel-1 tocsection-4"><a href="#Stellar_evolution"><span class="tocnumber">4</span> <span class="toctext">Stellar evolution</span></a></li> <li class="toclevel-1 tocsection-5"><a href="#Asymptomatic_giant_branch_stars"><span class="tocnumber">5</span> <span class="toctext">Asymptomatic giant branch stars</span></a> <ul> <li class="toclevel-2 tocsection-6"><a href="#R_type_stars"><span class="tocnumber">5.1</span> <span class="toctext">R type stars</span></a></li> <li class="toclevel-2 tocsection-7"><a href="#N_type_stars"><span class="tocnumber">5.2</span> <span class="toctext">N type stars</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-8"><a href="#Peculiar_stars"><span class="tocnumber">6</span> <span class="toctext">Peculiar stars</span></a> <ul> <li class="toclevel-2 tocsection-9"><a href="#Wolf-Rayet_stars_(WR)"><span class="tocnumber">6.1</span> <span class="toctext">Wolf-Rayet stars (WR)</span></a></li> <li class="toclevel-2 tocsection-10"><a href="#T_Tauri_stars_(T)"><span class="tocnumber">6.2</span> <span class="toctext">T Tauri stars (T)</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-11"><a href="#References"><span class="tocnumber">7</span> <span class="toctext">References</span></a></li> <li class="toclevel-1 tocsection-12"><a href="#See_also"><span class="tocnumber">8</span> <span class="toctext">See also</span></a></li> </ul> </div> <h2><span class="mw-headline" id="History">History</span></h2> <p>In 1801, William Hyde Wollaston (1766-1828) noted absorption lines in the solar spectrum. The solar spectrum was not a continuous band of colour and included a series of dark lines. Wollaston perceived this as a possible boundary between colours.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5">[5]</a></sup> </p><p>Joseph von Fraunhofer (1787-1826) in 1814, studied this phenomena and concluded that the dark bands represented specific wavelengths.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6">[6]</a></sup> </p><p>In 1863, Sir William Huggins (1824-1910) employed the research of Fraunhofer, Gustav Robert Kirchhoff and Robert Wilhelm Eberhard Bunsen to lay the final piece of the puzzle in place and compared these solar spectrums with other stars and terrestrial substances.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7">[7]</a></sup> In this way it was demonstrated that the dark bands, now known as Fraunhofer Lines, are the absorption lines for chemical elements present in the stars. Specific chemicals present in the outer layers of a star absorb specific wavelengths creating the dark lines. This also showed that the stars are made of the same substances here on Earth.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8">[8]</a></sup> </p><p>While this work provided for the foundation of the field of spectroscopy it also provided a tool for astrophysics and astronomy. These distinctive spectral lines which provide information about the chemical composition of the stars have become the basis for their classification. </p> <h2><span class="mw-headline" id="Classification_system">Classification system</span></h2> <p>The stars are ranked from hottest to coldest: </p> <table class="wikitable"> <tbody><tr> <th>Class </th> <th>Temperature </th> <th abbr="color">Conventional vs Apparent color <p><sup id="cite_ref-9" class="reference"><a href="#cite_note-9">[9]</a></sup> </p> </th> <th abbr="Characteristics">Characteristics <p><sup id="cite_ref-10" class="reference"><a href="#cite_note-10">[10]</a></sup> </p> </th> <th>Mass <sup id="cite_ref-11" class="reference"><a href="#cite_note-11">[11]</a></sup> </th> <th>Radius <sup id="cite_ref-12" class="reference"><a href="#cite_note-12">[12]</a></sup> </th> <th>Luminosity <sup id="cite_ref-13" class="reference"><a href="#cite_note-13">[13]</a></sup> </th> <th>Hydrogen lines </th> <th>% of all MSSs<sup id="cite_ref-14" class="reference"><a href="#cite_note-14">[14]</a></sup><sup id="cite_ref-15" class="reference"><a href="#cite_note-15">[15]</a></sup> </th></tr> <tr style="background:#9bb0ff;"> <th style="background:#9bb0ff;"><a href="#Class_O">O</a> </th> <td>30,000–60,000 K </td> <td style="background:#9aafff;">blue/blue </td> <td style="background:#aabfff;">Ionized He & metals; <p>weak H </p> </td> <td>10-70 <a href="/wiki/index.php?title=Solar_mass&action=edit&redlink=1" class="new" title="Solar mass (page does not exist)">M<sub>☉</sub></a> </td> <td>15 <a href="/wiki/index.php?title=Solar_radius&action=edit&redlink=1" class="new" title="Solar radius (page does not exist)">R<sub>☉</sub></a> </td> <td>1,400,000 <a href="/wiki/index.php?title=Solar_luminosity&action=edit&redlink=1" class="new" title="Solar luminosity (page does not exist)">L<sub>☉</sub></a> </td> <td>Weak </td> <td>~0.00003% </td></tr> <tr style="background:#aabfff;"> <th style="background:#abbfff;"><a href="#Class_B">B</a> </th> <td>10,000–30,000 K </td> <td style="background:#cad7ff;">blue white/blue white to white </td> <td style="background:#cad7ff;">Neutral He, ionized metals, stronger H </td> <td>18 <a href="/wiki/index.php?title=Solar_mass&action=edit&redlink=1" class="new" title="Solar mass (page does not exist)">M<sub>☉</sub></a> </td> <td>7 <a href="/wiki/index.php?title=Solar_radius&action=edit&redlink=1" class="new" title="Solar radius (page does not exist)">R<sub>☉</sub></a> </td> <td>20,000 <a href="/wiki/index.php?title=Solar_luminosity&action=edit&redlink=1" class="new" title="Solar luminosity (page does not exist)">L<sub>☉</sub></a> </td> <td>Medium </td> <td>0.13% </td></tr> <tr style="background:#cad7ff;"> <th style="background:#cad7ff;"><a href="#Class_A">A</a> </th> <td>7,500–10,000 K </td> <td style="background:#f8f7ff;">white/white </td> <td style="background:#f8f7ff;">Balmer H dominant, singly-ionized metals </td> <td>3.1 <a href="/wiki/index.php?title=Solar_mass&action=edit&redlink=1" class="new" title="Solar mass (page does not exist)">M<sub>☉</sub></a> </td> <td>2.1 <a href="/wiki/index.php?title=Solar_radius&action=edit&redlink=1" class="new" title="Solar radius (page does not exist)">R<sub>☉</sub></a> </td> <td>80 <a href="/wiki/index.php?title=Solar_luminosity&action=edit&redlink=1" class="new" title="Solar luminosity (page does not exist)">L<sub>☉</sub></a> </td> <td>Strong </td> <td>0.6% </td></tr> <tr style="background:#f8f7ff;"> <th style="background:#f8f7ff;"><a href="#Class_F">F</a> </th> <td>6,000–7,500 K </td> <td style="background:#fff4ea;">yellowish white/white </td> <td style="background:#f8f7ff;">H weaker, neutral & singly-ionized metals </td> <td>1.7 <a href="/wiki/index.php?title=Solar_mass&action=edit&redlink=1" class="new" title="Solar mass (page does not exist)">M<sub>☉</sub></a> </td> <td>1.3 <a href="/wiki/index.php?title=Solar_radius&action=edit&redlink=1" class="new" title="Solar radius (page does not exist)">R<sub>☉</sub></a> </td> <td>6 <a href="/wiki/index.php?title=Solar_luminosity&action=edit&redlink=1" class="new" title="Solar luminosity (page does not exist)">L<sub>☉</sub></a> </td> <td>Medium </td> <td>3% </td></tr> <tr style="background:#fff4ea;"> <th style="background:#fff4ea;"><a href="#Class_G">G</a> </th> <td>5,000–6,000 K </td> <td style="background:#fff2a1;">yellow/yellow </td> <td style="background:#fff4ea;">Singly ionized Ca, H weaker, neutral metals </td> <td>1.1 <a href="/wiki/index.php?title=Solar_mass&action=edit&redlink=1" class="new" title="Solar mass (page does not exist)">M<sub>☉</sub></a> </td> <td>1.1 <a href="/wiki/index.php?title=Solar_radius&action=edit&redlink=1" class="new" title="Solar radius (page does not exist)">R<sub>☉</sub></a> </td> <td>1.2 <a href="/wiki/index.php?title=Solar_luminosity&action=edit&redlink=1" class="new" title="Solar luminosity (page does not exist)">L<sub>☉</sub></a> </td> <td>Weak </td> <td>8% </td></tr> <tr style="background:#ffd2a1;"> <th style="background:#ffd2a1;"><a href="#Class_K">K</a> </th> <td>3,500–5,000 K </td> <td style="background:#ffc46f;">orange/yellow orange </td> <td style="background:#ffd2a1;">Neutral Metals, molecular bands begin to appear </td> <td>0.8 <a href="/wiki/index.php?title=Solar_mass&action=edit&redlink=1" class="new" title="Solar mass (page does not exist)">M<sub>☉</sub></a> </td> <td>0.9 <a href="/wiki/index.php?title=Solar_radius&action=edit&redlink=1" class="new" title="Solar radius (page does not exist)">R<sub>☉</sub></a> </td> <td>0.4 <a href="/wiki/index.php?title=Solar_luminosity&action=edit&redlink=1" class="new" title="Solar luminosity (page does not exist)">L<sub>☉</sub></a> </td> <td>Very weak </td> <td>13% </td></tr> <tr style="background:#ffcc6f;"> <th style="background:#ffcc6f;"><a href="#Class_M">M</a> </th> <td>2,000–3,500 K </td> <td style="background:#ff6060;">red/orange red </td> <td style="background:#ffcc6f;">Ti oxide molecular lines; neutral metals </td> <td>0.3 <a href="/wiki/index.php?title=Solar_mass&action=edit&redlink=1" class="new" title="Solar mass (page does not exist)">M<sub>☉</sub></a> </td> <td>0.4 <a href="/wiki/index.php?title=Solar_radius&action=edit&redlink=1" class="new" title="Solar radius (page does not exist)">R<sub>☉</sub></a> </td> <td>0.04 <a href="/wiki/index.php?title=Solar_luminosity&action=edit&redlink=1" class="new" title="Solar luminosity (page does not exist)">L<sub>☉</sub></a> </td> <td>Very weak </td> <td>>78% </td></tr></tbody></table> <p><sup id="cite_ref-16" class="reference"><a href="#cite_note-16">[16]</a></sup><sup id="cite_ref-17" class="reference"><a href="#cite_note-17">[17]</a></sup> </p> <h2><span class="mw-headline" id="Luminosity_classes">Luminosity classes</span></h2> <p>Another schema for classifying stars is the Yerkes classification,<sup id="cite_ref-18" class="reference"><a href="#cite_note-18">[18]</a></sup> also known as M-K established in 1943.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19">[19]</a></sup> This classification scheme measures surface gravities of stars by measuring the shape and nature of certain spectral lines. </p> <table class="wikitable"> <tbody><tr style="background:#9bb0ff;"> <th style="background:#9bb0ff;">Ia </th> <td>Most luminous supergiants </td></tr> <tr style="background:#aabfff;"> <th style="background:#abbfff;">Ib </th> <td>Less luminous super giants </td></tr> <tr style="background:#cad7ff;"> <th style="background:#cad7ff;">II </th> <td>Luminous giants </td></tr> <tr style="background:#f8f7ff;"> <th style="background:#f8f7ff;">III </th> <td>Normal giants </td></tr> <tr style="background:#fff4ea;"> <th style="background:#fff4ea;">IV </th> <td>Subgiants </td></tr> <tr style="background:#ffd2a1;"> <th style="background:#ffd2a1;">V </th> <td>Main sequence stars (dwarf) </td></tr> <tr style="background:#ffd2a1;"> <th style="background:#ffd2a1;">VI </th> <td>Main sequence stars (subdwarf) </td></tr> <tr style="background:#ffd2a1;"> <th style="background:#ffd2a1;">VII </th> <td>Main sequence stars (white dwarf) </td></tr></tbody></table> <p><sup id="cite_ref-20" class="reference"><a href="#cite_note-20">[20]</a></sup> </p> <h2><span class="mw-headline" id="Stellar_evolution">Stellar evolution</span></h2> <p>Depending on their mass, stars will undergo various stages in greatly varying lengths of time. Larger stars are shorter lived than the smallest and their transitions from one stage to another as they burn their fuel can be gradual, such as a red dwarf, or very explosive, such as the largest supergiant. The diagramme below shows the early stage of each class of star and their intermediate and final stages. The length of time roughly corresponds to distance they are spaced on the diagramme. </p> <table class="wikitable"> <tbody><tr style=""> <th style="">Early stage </th> <td> </td> <td> </td> <td> </td> <td> </td></tr> <tr style="background:#9bb0ff;"> <th style="background:#9bb0ff;">Protostar </th> <td>Blue supergiant </td> <td>Supernova (final stage) </td> <td> </td> <td> </td></tr> <tr style="background:#aabfff;"> <th style="background:#abbfff;">Protostar </th> <td>Blue supergiant </td> <td> </td> <td>Black hole (final stage) </td> <td> </td></tr> <tr style="background:#cad7ff;"> <th style="background:#cad7ff;">Protostar </th> <td>Blue supergiant </td> <td>Type II Supernova </td> <td> </td> <td>Black hole (final stage) </td></tr> <tr style="background:#f8f7ff;"> <th style="background:#f8f7ff;">Protostar </th> <td>Blue supergiant </td> <td>Red giant </td> <td>Type II supernova </td> <td>Neutron Star (final stage) </td></tr> <tr style="background:#fff4ea;"> <th style="background:#fff4ea;">Protostar </th> <td>Sun-like star </td> <td>Red giant </td> <td>Planetary nebula </td> <td>White dwarf (final stage) </td></tr> <tr style="background:#ffd2a1;"> <th style="background:#ffd2a1;">Protostar </th> <td>Red dwarf </td> <td> </td> <td>Red Dwarf </td> <td>White Dwarf (final stage) </td></tr> <tr style="background:#ffd2a1;"> <th style="background:#ffd2a1;">Protostar </th> <td>Brown dwarf </td> <td> </td> <td> </td> <td>Brown dwarf (final stage) </td></tr></tbody></table> <p><sup id="cite_ref-21" class="reference"><a href="#cite_note-21">[21]</a></sup> </p><p>Until recently it was believed that blue supergiants would either burn their fuel and collapse into a black hole or undergo a massive explosion and then form a black hole. However, the recent discovery of SN 2006gy shows that at least in this one case, the initial explosion is so complete the largest blue supergiant is completely obliterated.<sup id="cite_ref-22" class="reference"><a href="#cite_note-22">[22]</a></sup> </p><p>For stars with a solar mass of about 10-25 (10-25 times the mass of earth's Sun) they will first become red giants. Usually they remain red giants until they explode. For stars with greater masses (more than approximately 20 solar masses) the process of evaporation and radiation pressure may blow out the outer layers and forming a blue giant before it explodes. SN1987A, for example, was apparently a blue giant before it exploded.<sup id="cite_ref-23" class="reference"><a href="#cite_note-23">[23]</a></sup> </p> <h2><span class="mw-headline" id="Asymptomatic_giant_branch_stars">Asymptomatic giant branch stars</span></h2> <h3><span class="mw-headline" id="R_type_stars">R type stars</span></h3> <h3><span class="mw-headline" id="N_type_stars">N type stars</span></h3> <h2><span class="mw-headline" id="Peculiar_stars">Peculiar stars</span></h2> <h3><span id="Wolf-Rayet_stars_.28WR.29"></span><span class="mw-headline" id="Wolf-Rayet_stars_(WR)">Wolf-Rayet stars (WR)</span></h3> <h3><span id="T_Tauri_stars_.28T.29"></span><span class="mw-headline" id="T_Tauri_stars_(T)">T Tauri stars (T)</span></h3> <h2><span class="mw-headline" id="References">References</span></h2> <div class="references-small"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><a href="#cite_ref-1">↑</a></span> <span class="reference-text">Schema, the plural of scheme, refers to a way of organising or diagramming a body of facts or theories, virtually anything related that can be organised. The visible light spectrum scheme, for example, is ROYGBIV: red, orange, yellow, green, blue, indigo, and violet.</span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><a href="#cite_ref-2">↑</a></span> <span class="reference-text">Note: based on the work of Annie Cannon and other astronomers from the Harvard College Observatory</span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><a href="#cite_ref-3">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.sdsc.edu/ScienceWomen/cannon.html">Annie Jump Cannon</a> 1883-1941</span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><a href="#cite_ref-4">↑</a></span> <span class="reference-text">A popular mnemonic for this (originally alphabetical) sequence is <b>O</b>h <b>B</b>e <b>A</b> <b>F</b>ine <b>G</b>irl, <b>K</b>iss <b>M</b>e <a rel="nofollow" class="external text" href="http://www.shef.ac.uk/physics/people/pacrowther/obafgkmrns.html">Mnemonics for the Harvard Spectral Classification Scheme</a></span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><a href="#cite_ref-5">↑</a></span> <span class="reference-text">Note: Contemporary sources give varying dates for this discovery between 1801 and 1807. However, Sir William Huggins, in 1910, places this date at 1792. see <a rel="nofollow" class="external text" href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1910PASP...22..149C&defaultprint=YES&filetype=.pdf">Sir William Huggins</a> W. W. Campbell (1910). Astronomical Society of the Pacific vol. XXIII, no. 133 page 153.; <a rel="nofollow" class="external text" href="http://chem.ch.huji.ac.il/history/wollaston.html">William Hyde Wollaston</a> Hebrew University of Jerusalem, Institute of Chemistry; <a rel="nofollow" class="external text" href="http://www.acmi.net.au/AIC/WOLLASTON_BIO.html">William Hyde Wollaston : 1766 – 1828</a> Dean P. Currier. Australian Centre for the moving image; <a rel="nofollow" class="external text" href="http://www.zeiss.com/c12567a100537ab9/Contents-Frame/056301e9396f8be0c125695a002468e6">William Hyde Wollaston</a> Carl Zeiss AG; <a rel="nofollow" class="external text" href="http://micro.magnet.fsu.edu/optics/timeline/people/wollaston.html">William Hyde Wollaston</a> Michael W. Davidson, Florida State University; <a rel="nofollow" class="external text" href="http://www.hao.ucar.edu/Public/education/Timeline.D.html">History of Solar Physics - A Time Line of Great Moments 1800-1999</a> <a href="/wiki/National_Center_for_Atmospheric_Research" title="National Center for Atmospheric Research">National Center for Atmospheric Research</a> & The UCAR Office Programs; <a rel="nofollow" class="external text" href="http://www.hao.ucar.edu/Public/education/bios/wollaston.html">William Hyde Wollaston (1766-1828)</a> High Altitude Observatory, National Center for Atmospheric Research & The UCAR Office Programs </span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><a href="#cite_ref-6">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.hao.ucar.edu/Public/education/bios/fraunhofer.html">Joseph von Fraunhofer</a> High Altitude Observatory, National Center for Atmospheric Research & The UCAR Office Programs; <a rel="nofollow" class="external text" href="http://www.newadvent.org/cathen/06250a.htm">Joseph von Fraunhofer</a> New Advent Catholic Encyclopedia; <a rel="nofollow" class="external text" href="http://www.fraunhofer.de/fhg/Images/joseph_tcm6-5806.pdf">Joseph von Fraunhofer</a> Fraunhofer-Gesellschaft</span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><a href="#cite_ref-7">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://seds.org/messier/xtra/Bios/huggins.html">William Huggins (February 7, 1824 - May 12, 1910)</a> Messier Catalog, Students for the Exploration and Development of Space; <a rel="nofollow" class="external text" href="http://www.phys-astro.sonoma.edu/BruceMedalists/Huggins/index.html">William Huggins 1904 Bruce Medalist</a> Astronomical Society of the Pacific; <a rel="nofollow" class="external text" href="http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1910PASP...22..149C&defaultprint=YES&filetype=.pdf">Sir William Huggins, K.C.B., O.M.</a> W.W. Campbell (1910) Astronomical Society of the Pacific; <a rel="nofollow" class="external text" href="http://chem.ch.huji.ac.il/history/kirchhoff.htm">Gustav Robert Kirchhoff </a> Institute of Chemistry, Hebrew University of Jerusalem</span> </li> <li id="cite_note-8"><span class="mw-cite-backlink"><a href="#cite_ref-8">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://laserstars.org/spectra/Fraunhofer.html">Identificatio of spectral lines-History of Fraunhofer lines</a> University of Ottawa; <a rel="nofollow" class="external text" href="http://www.genesismission.org/educate/scimodule/SSWPrOptPDFs/5HereComesLight/FranhoferLines-ST-PO.pdf">The Fraunhofer Lines</a> Jet Propulsion Lab, California Institute of Technology, NASA</span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><a href="#cite_ref-9">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html">The Colour of Stars</a>. Australia Telescope Outreach and Education (December 21 2004). Retrieved on 2007-10-26. — Explains the reason for the difference in color perception.</span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><a href="#cite_ref-10">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://csep10.phys.utk.edu/astr162/lect/hr/hr.html">The Hertzasprung-Russell diagram (subsection The Harvard spectral sequence)</a>. University of Tennessee, Dept of Physics and Astronomy (unknown). Retrieved on 2007-10-26. — Details various aspects of stellar classification.</span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><a href="#cite_ref-11">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://observe.arc.nasa.gov/nasa/space/stellardeath/stellardeath_6.html">NASA glossary</a> Solar Mass. Earth's sun is one solar mass. Equal to about 2 X 10E30 kg or about 333,000 time the mass of the earth</span> </li> <li id="cite_note-12"><span class="mw-cite-backlink"><a href="#cite_ref-12">↑</a></span> <span class="reference-text"> Solar Radius. Earth's sun is the standard with one solar radius equal to about 6.960 X 10E8 km. This is about twice the distance of the earth from the moon, 110 times the radius of earth, and 0.004652 AU (astronomical unit), the average distance of the earth from the sun. <a rel="nofollow" class="external text" href="http://zebu.uoregon.edu/~imamura/208/jan11/radius.html">Solar Radius</a> University of Oregon. <a rel="nofollow" class="external text" href="http://umbra.nascom.nasa.gov/spartan/the_corona.html">The Corona</a> Spartan 201. NASA</span> </li> <li id="cite_note-13"><span class="mw-cite-backlink"><a href="#cite_ref-13">↑</a></span> <span class="reference-text"> Solar Luminosity. The standard is earth's sun equal to one solar luminosity. The luminosity of the sun is about 3.827 X 10E26 watts or 3.827 X 10E33 ergs</span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><a href="#cite_ref-14">↑</a></span> <span class="reference-text">MSS = <b>M</b>ain <b>S</b>equence <b>S</b>tar</span> </li> <li id="cite_note-15"><span class="mw-cite-backlink"><a href="#cite_ref-15">↑</a></span> <span class="reference-text">LeDrew, G.; The Real Starry Sky, Journal of the Royal Astronomical Society of Canada, Vol. 95, No. 1 (whole No. 686, February 2001), pp. 32–33</span> </li> <li id="cite_note-16"><span class="mw-cite-backlink"><a href="#cite_ref-16">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.astrophysical.org/starclassification.php">Star classification</a></span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><a href="#cite_ref-17">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external autonumber" href="http://lithops.as.arizona.edu/~jill/EPO/Stars/StarPower2.pdf">[1]</a> Bechtold, Jill, Dept of Astronomy, Steward Observatory, University of Arizona</span> </li> <li id="cite_note-18"><span class="mw-cite-backlink"><a href="#cite_ref-18">↑</a></span> <span class="reference-text">Yerkes Observatory</span> </li> <li id="cite_note-19"><span class="mw-cite-backlink"><a href="#cite_ref-19">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.journals.uchicago.edu/AJ/journal/issues/v121n4/200462/200462.html">The physical basis of luminosity classification in the late A-, F-, and early G-type Stars. I. Precise spectral types for 372 stars</a> Gray, R.O., Napier, M.G., Winkler, L.I. (2001) The Astronomical Journal April. 121:2148-2158. The American Astronomical Society; MKK are the initials of the authors Morgan, William W., Keenan, Philip C. and Kellman, Edith </span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><a href="#cite_ref-20">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.shef.ac.uk/physics/people/pacrowther/spectral_classification.html">Classification of Stellar spectra</a> website of Dept of Physics and Astronomy, University of Sheffield. Author: Jesse S. Allen, High Energy Astrophysics Science Archive Research Center. See <a rel="nofollow" class="external autonumber" href="http://heasarc.gsfc.nasa.gov/docs/journal/staff5.html">[2]</a> The page is also carried by Iowa Robotic Telescope Facilities, University of Iowa at <a rel="nofollow" class="external autonumber" href="http://www-astro.physics.uiowa.edu/~kgg/teaching/general62/spectral_classification.html">[3]</a></span> </li> <li id="cite_note-21"><span class="mw-cite-backlink"><a href="#cite_ref-21">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://chandra.harvard.edu/photo/2007/sn2006gy/sn2006gy_newline.jpg">A new line of stellar evolution</a> <a rel="nofollow" class="external text" href="http://chandra.harvard.edu/resources/illustrations/supernova.html">Supernovas and Remnants</a> Chandra X-ray Observatory Retrieved 30, Oct, 2007</span> </li> <li id="cite_note-22"><span class="mw-cite-backlink"><a href="#cite_ref-22">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://chandra.harvard.edu/resources/illustrations/supernova.html">Supernovas and remnants</a> Chandra X-ray Observatory</span> </li> <li id="cite_note-23"><span class="mw-cite-backlink"><a href="#cite_ref-23">↑</a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://chandra.harvard.edu/resources/faq/sources/snr/snr-28.html">Supernova remnants and neutron stars</a> Chandra X-ray Observatory</span> </li> </ol></div> </div> <h2><span class="mw-headline" id="See_also">See also</span></h2> <p><a href="/wiki/Wolf_359_(star)" title="Wolf 359 (star)">Wolf 359 (star)</a> </p><p><a href="/wiki/Proxima_Centauri_(star)" title="Proxima Centauri (star)">Proxima Centauri (star)</a> </p><p><a href="/wiki/Electromagnetic_spectrum" title="Electromagnetic spectrum">Electromagnetic spectrum</a> </p><p><a href="/wiki/Infrared_light" title="Infrared light">Infrared light</a> </p><p><a href="/wiki/Light" title="Light">Light</a> </p>  </div> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://citizendium.org/wiki/index.php?title=Stellar_classification_(astrophysics)&oldid=989420">https://citizendium.org/wiki/index.php?title=Stellar_classification_(astrophysics)&oldid=989420</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Special:Categories" title="Special:Categories">Categories</a>: <ul><li><a href="/wiki/Category:CZ_Live" title="Category:CZ Live">CZ Live</a></li><li><a href="/wiki/Category:Astronomy_Workgroup" title="Category:Astronomy Workgroup">Astronomy Workgroup</a></li><li><a href="/wiki/Category:Articles_written_in_British_English" title="Category:Articles written in British English">Articles written in British English</a></li><li><a href="/wiki/Category:All_Content" title="Category:All Content">All Content</a></li><li><a href="/wiki/Category:Astronomy_Content" title="Category:Astronomy Content">Astronomy Content</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:Astronomy_tag" title="Category:Astronomy tag">Astronomy tag</a></li><li><a href="/wiki/Category:Suggestion_Bot_Tag" title="Category:Suggestion Bot Tag">Suggestion Bot Tag</a></li></ul></div></div> </div> </div> <div id="mw-navigation"> <h2>Navigation menu</h2> <div id="mw-head"> <nav id="p-personal" class="vector-menu mw-portlet mw-portlet-personal vector-user-menu-legacy" aria-labelledby="p-personal-label" role="navigation" > <h3 id="p-personal-label" class="vector-menu-heading " > <span class="vector-menu-heading-label">Personal tools</span> </h3> <div class="vector-menu-content"> <ul class="vector-menu-content-list"><li id="pt-login" class="mw-list-item"><a href="/wiki/index.php?title=Special:UserLogin&returnto=Stellar+classification+%28astrophysics%29" title="To edit pages, [[Special:RequestAccount|get a contributor account]]. 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