Editing Spectral (Stellar) Classification System

              <h2 align=center><b>Spectral (Stellar) Classification System</b></h2>
              <P><font size="2">The original version of the current MK system 
                was defined by Morgan, Keenan, and Kellman (1943), and a revised 
                list of standards was published in 1953 by Morgan and Johnson. 
                Additional refinements have been added since then.</font></P>
              <P align=center><b>MK Spectral Classification System (Standard)</b></P>

              <P align=center> 
              <CENTER>
                <TABLE borderColor=#008080 cellSpacing=4 cellPadding=1 width=578 border=1>
                      <TR> 
                      <TD vAlign=center width="12%"> <h5 align=center><b>Class**
                             </b></h5></TD>
                      <TD vAlign=center width="33%"> <h5 align=center><b>Color
                             </b></h5></TD>
                      <TD vAlign=center width="23%"> <h5 align=center><b>Temperature 
                             (K)</b></h5></TD>
                      <TD vAlign=center width="53%"> <h5 align=center><strong>Composition
                             </strong></h5></TD>
                    </TR>
                    <TR> 
                      <TD vAlign=center width="12%"> <P align=center>O</P></TD>
                      <TD vAlign=center width="13%"> <P align=center>Dark Blue</P></TD>
                      <TD vAlign=center width="23%"> <P align=center>28,000-50,000</P></TD>

                      <TD vAlign=center width="53%"> <P align=center>ionized atoms, 
                          especially helium</P></TD>
                    </TR>
                    <TR> 
                      <TD vAlign=center width="12%"> <P align=center>B</P></TD>
                      <TD vAlign=center width="13%"> <P align=center>Blue</P></TD>
                      <TD vAlign=center width="23%"> <P align=center>10,000-28,000</P></TD>

                      <TD vAlign=center width="53%"> <P align=center>neutral helium, 
                          some hydrogen</P></TD>
                    </TR>
                    <TR> 
                      <TD vAlign=center width="12%"> <P align=center>A</P></TD>
                      <TD vAlign=center width="13%"> <P align=center>Light Blue</P></TD>
                      <TD vAlign=center width="23%"> <P align=center>7,500-10,000</P></TD>

                      <TD vAlign=center width="53%"> <P align=center>strong hydrogen, 
                          some ionized metals</P></TD>
                    </TR>
                    <TR> 
                      <TD vAlign=center width="12%"> <P align=center>F</P></TD>
                      <TD vAlign=center width="13%"> <P align=center>White</P></TD>
                      <TD vAlign=center width="23%"> <P align=center>6,000-7,500</P></TD>

                      <TD vAlign=center width="53%"> <P align=center>hydrogen 
                          and ionized metals; calcium and iron</P></TD>
                    </TR>
                    <TR> 
                      <TD vAlign=center width="12%"> <P align=center>G</P></TD>
                      <TD vAlign=center width="13%"> <P align=center>Yellow</P></TD>
                      <TD vAlign=center width="23%"> <P align=center>5,000-6,000</P></TD>

                      <TD vAlign=center width="53%"> <P align=center>ionized calcium; 
                          both neutral and ionized metals</P></TD>
                    </TR>
                    <TR> 
                      <TD vAlign=center width="12%"> <P align=center>K</P></TD>
                      <TD vAlign=center width="13%"> <P align=center>Orange</P></TD>
                      <TD vAlign=center width="23%"> <P align=center>3,500-5,000</P></TD>

                      <TD vAlign=center width="53%"> <P align=center>Neutral metals</P></TD>
                    </TR>
                    <TR> 
                      <TD vAlign=center width="12%"> <P align=center>M</P></TD>
                      <TD vAlign=center width="13%"> <P align=center>Red</P></TD>
                      <TD vAlign=center width="23%"> <P align=center>2,500-3,500</P></TD>

                      <TD vAlign=center width="53%"> <P align=center>Strong molecules; 
                          titanium oxide, neutral calcium</P></TD>
                    </TR>
              </TABLE>

<BLOCKQUOTE ALIGN="CENTER">**Three additional categories are also 
                in the scheme: R, N, and S types, which were later realized to 
                represent stars with peculiar heavy-metal abundances. Other types 
                (Q for novae, W for Wolf-Rayet stars, T for T Tauri stars, <I>etc...</I>) 
                are encountered infrequently. Thus, the above listing is considered 
                the standard classification scheme, and R, N, S, T, Q, W, etc... 
                are addendums in the rare cases they are observed.**</BLOCKQUOTE>

<BLOCKQUOTE ALIGN="CENTER">Each class is subdivided into 10 categories by decreasing 
                temperature within each class. This scale ranges from 0 (the hottest) 
                to 9 (the coolest), i.e., A0, A1, A2, ... A8, A9. So, an A4 star 
                is hotter then an A7. For instance, Vega is an A0 and the Sun 
                is a G2.
<BLOCKQUOTE ALIGN="CENTER">Stars are then further classified 
                by their type into six luminosity categories by the Yerkes scheme, 
                as seen in the Hertzsprung-Russell Diagram below (based on Luminosity 
                and Temperature (K)):: 
<STRONG>
:Ia: Most Luminous Supergiants 
:Ib: Less Luminous Supergiants
:II: Luminous Giants
:III: Normal Giants
:IV: Sub-Giants
:V: Main Sequence (Dwarfs)</STRONG>
<BLOCKQUOTE ALIGN="CENTER">''Thus, Sol, is categorized a G2V classification. That is, a G-Type 2 
                Main Sequence star.''</BLOCKQUOTE>

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