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+<sect1 id="ai-ellipgal">
+<sect1info>
+<author>
+<firstname>Jasem</firstname>
+<surname>Mutlaq</surname>
+<affiliation><address>
+</address></affiliation>
+</author>
+</sect1info>
+
+<title>Elliptical Galaxies</title>
+<indexterm><primary>Elliptical Galaxies</primary>
+</indexterm>
+
+<para> Elliptical galaxies are spheroidal concentrations of billions
+of stars that resemble Globular Clusters on a grand scale.  They have
+very little internal structure; the density of stars declines smoothly
+from the concentrated center to the diffuse edge, and they can have a
+broad range of ellipticities (or aspect ratios).  They typically
+contain very little interstellar gas and dust, and no young stellar
+populations (although there are exceptions to these rules).  Edwin
+Hubble referred to Elliptical galaxies as <quote>early-type</quote>
+galaxies, because he thought that they evolved to become Spiral
+Galaxies (which he called <quote>late-type</quote> galaxies).
+Astronomers actually now believe the opposite is the case (&ie;, that
+Spiral galaxies can turn into Elliptical galaxies), but Hubble's
+early- and late-type labels are still used.  </para>
+
+<para>
+Once thought to be a simple galaxy type, ellipticals are now known to
+be quite complex objects.  Part of this complexity is due
+to their amazing history: ellipticals are thought to be the end
+product of the merger of two Spiral galaxies.  You can
+view a computer simulation MPEG movie of such a merger at <ulink
+url="http://oposite.stsci.edu/pubinfo/pr/2002/11/vid/v0211d3.mpg">
+this NASA HST webpage</ulink> (warning: the file is 3.4 MB).
+</para>
+
+<para>
+Elliptical galaxies span a very wide range of sizes and
+luminosities, from giant Ellipticals hundreds of thousands of light
+years across and nearly a trillion times brighter than the sun, to
+dwarf Ellipticals just a bit brighter than the average globular
+cluster.  They are divided to several morphological classes:
+</para>
+
+<variablelist>
+<varlistentry>
+<term>cD galaxies:</term>
+<listitem><para>
+Immense and bright objects that can
+measure nearly 1 Megaparsec (3 million light years) across.  These
+titans are only found near the centers of large, dense clusters of
+galaxies, and are likely the result of many galaxy
+mergers.</para></listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Normal Elliptical galaxies</term>
+<listitem><para>Condensed Object with
+relatively high central surface brightness. They include the giant
+ellipticals (gE'e), intermediate-luminosity ellipticals (E's), and
+compact ellipticals.</para></listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Dwarf elliptical galaxies (dE's)</term>
+<listitem><para> This class of
+galaxies is fundamentally different from normal ellipticals. Their
+diameters on the order of 1 to 10 kiloparsec with surface brightness
+that is much lower than normal ellipticals, giving them a much more
+diffuse appearance. They display the same characteristic gradual
+decline of star density from a relatively dense core out to a diffuse
+periphery.</para></listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Dwarf spheroidal galaxies (dSph's)</term>
+<listitem><para>Extreme low-luminosity, low
+surface-brightness and have only been observed in the vicinity of the
+Milky Way, and possibly other very nearby galaxy groups, such as the
+Leo group.  Their absolute magnitudes are only -8 to -15 mag.
+The Draco dwarf spheroidal galaxy has an absolute magnitude of -8.6,
+making it fainter than the average globular cluster in the Milky Way!
+</para></listitem>
+</varlistentry>
+
+<varlistentry>
+<term>Blue compact dwarf galaxies (BCD's)</term>
+<listitem>
+<para> Small galaxies that are unusually
+blue. Thehave photometric colors of B-V = 0.0 to 0.30 mag, which is
+typical for relatively young stars of <firstterm>spectral type</firstterm> A.
+This suggests that BCDs
+are currently actively forming stars.  These systems also have
+abundant interstellar gas (unlike other Elliptical galaxies).
+</para></listitem>
+</varlistentry>
+</variablelist>
+
+<tip>
+<para>
+You can see examples of Elliptical galaxies in &kstars;, using the Find
+Object window
+(<keycombo action="simul">&Ctrl;<keycap>F</keycap></keycombo>).
+Search for NGC 4881, which is the Giant cD galaxy in the Coma
+cluster of galaxies.  M 86 is a normal Elliptical galaxy in the Virgo
+cluster of galaxies.  M 32 is a dwarf Elliptical that is a satellite
+of our neighbor, the Andromeda galaxy (M 31).  M 110 is another
+satellite of M 31 that is a borderline dwarf spheroidal galaxy
+(<quote>borderline</quote> because it is somewhat brighter than most other
+dwarf spheroidals).
+</para>
+</tip>
+</sect1>