Copy the KDE 3.5 branch to branches/trinity for new KDE 3.5 features.

BUG:215923


git-svn-id: svn://anonsvn.kde.org/home/kde/branches/trinity/kdeedu@1054174 283d02a7-25f6-0310-bc7c-ecb5cbfe19da

1 files changed, 152 insertions, 0 deletions

diff --git a/doc/kstars/skycoords.docbook b/doc/kstars/skycoords.docbook
new file mode 100644
index 00000000..1017be06
--- /dev/null
+++ b/doc/kstars/skycoords.docbook
@@ -0,0 +1,152 @@
+<sect1 id="ai-skycoords">
+<sect1info>
+<author>
+<firstname>Jason</firstname>
+<surname>Harris</surname>
+</author>
+</sect1info>
+<title>Celestial Coordinate Systems</title>
+<para>
+<indexterm><primary>Celestial Coordinate Systems</primary>
+<secondary>Overview</secondary></indexterm>
+A basic requirement for studying the heavens is determining where in the
+sky things are.  To specify sky positions, astronomers have developed
+several <firstterm>coordinate systems</firstterm>.  Each uses a coordinate grid
+projected on the <link linkend="ai-csphere">Celestial Sphere</link>, in
+analogy to the <link linkend="ai-geocoords">Geographic coordinate
+system</link> used on the surface of the Earth.  The coordinate systems
+differ only in their choice of the <firstterm>fundamental plane</firstterm>,
+which divides the sky into two equal hemispheres along a <link
+linkend="ai-greatcircle">great circle</link>. (the fundamental plane of the
+geographic system is the Earth's equator). Each coordinate system is named for
+its choice of fundamental plane.
+</para>
+
+<sect2 id="equatorial">
+<title>The Equatorial Coordinate System</title>
+<indexterm><primary>Celestial Coordinate Systems</primary>
+<secondary>Equatorial Coordinates</secondary>
+<seealso>Celestial Equator</seealso>
+<seealso>Celestial Poles</seealso>
+<seealso>Geographic Coordinate System</seealso>
+</indexterm>
+<indexterm><primary>Right Ascension</primary><see>Equatorial Coordinates</see></indexterm>
+<indexterm><primary>Declination</primary><see>Equatorial Coordinates</see></indexterm>
+
+<para>
+The <firstterm>Equatorial coordinate system</firstterm> is probably the most
+widely used celestial coordinate system.  It is also the most closely related
+to the <link linkend="ai-geocoords">Geographic coordinate system</link>, because
+they use the same fundamental plane, and the same poles.  The projection of the
+Earth's equator onto the celestial sphere is called the
+<link linkend="ai-cequator">Celestial Equator</link>.
+Similarly, projecting the geographic Poles onto the celestial sphere defines the
+North and South <link linkend="ai-cpoles">Celestial Poles</link>.
+</para><para>
+However, there is an important difference between the equatorial and
+geographic coordinate systems: the geographic system is fixed to the
+Earth; it rotates as the Earth does.  The Equatorial system is
+fixed to the stars<footnote id="fn-precess"><para>actually, the equatorial
+coordinates are not quite fixed to the stars.  See <link
+linkend="ai-precession">precession</link>.  Also, if <link
+linkend="ai-hourangle">Hour Angle</link> is used in place of Right
+Ascension, then the Equatorial system is fixed to the Earth, not to the
+stars.</para></footnote>, so it appears to rotate across the sky with the stars,
+but of course it is really the Earth rotating under the fixed sky.
+</para><para>
+The <firstterm>latitudinal</firstterm> (latitude-like) angle of the Equatorial
+system is called <firstterm>Declination</firstterm> (Dec for short).  It
+measures the angle of an object above or below the Celestial Equator.  The
+<firstterm>longitudinal</firstterm> angle is called the <firstterm>Right
+Ascension</firstterm> (<acronym>RA</acronym> for short).  It measures the angle of an object East
+of the <link linkend="ai-equinox">Vernal Equinox</link>.  Unlike longitude,
+Right Ascension is usually measured in hours instead of degrees, because the
+apparent rotation of the Equatorial coordinate system is closely related to
+<link linkend="ai-sidereal">Sidereal Time</link> and <link
+linkend="ai-hourangle">Hour Angle</link>.  Since a full rotation of the sky
+takes 24 hours to complete, there are (360 degrees / 24 hours) = 15 degrees in
+one Hour of Right Ascension.
+</para>
+</sect2>
+
+<sect2 id="horizontal">
+<title>The Horizontal Coordinate System</title>
+
+<indexterm><primary>Celestial Coordinate Systems</primary>
+<secondary>Horizontal Coordinates</secondary>
+<seealso>Horizon</seealso>
+<seealso>Zenith</seealso>
+</indexterm>
+<indexterm><primary>Azimuth</primary><see>Horizontal Coordinates</see></indexterm>
+<indexterm><primary>Altitude</primary><see>Horizontal Coordinates</see></indexterm>
+<para>
+The Horizontal coordinate system uses the observer's local <link
+linkend="ai-horizon">horizon</link> as the Fundamental Plane.  This conveniently
+divides the sky into the upper hemisphere that you can see, and the lower
+hemisphere that you can't (because the Earth is in the way).  The pole of the
+upper hemisphere is called the <link linkend="ai-zenith">Zenith</link>.  The
+pole of the lower hemisphere is called the <firstterm>nadir</firstterm>.  The
+angle of an object above or below the horizon is called the
+<firstterm>Altitude</firstterm> (Alt for short).  The angle of an object around
+the horizon (measured from the North point, toward the East) is called the
+<firstterm>Azimuth</firstterm>.  The Horizontal Coordinate System is sometimes
+also called the Alt/Az Coordinate System.
+</para><para>
+The Horizontal Coordinate System is fixed to the Earth, not the Stars.
+Therefore, the Altitude and Azimuth of an object changes with time, as the
+object appears to drift across the sky.  In addition, because the Horizontal
+system is defined by your local horizon, the same object viewed from different
+locations on Earth at the same time will have different values of Altitude and
+Azimuth.
+</para><para>
+Horizontal coordinates are very useful for determining the Rise and Set times of
+an object in the sky.  When an object has Altitude=0 degrees, it is either
+Rising (if its Azimuth is &lt; 180 degrees) or Setting (if its Azimuth is &gt;
+180 degrees).
+</para>
+</sect2>
+
+<sect2 id="ecliptic">
+<title>The Ecliptic Coordinate System</title>
+
+<indexterm><primary>Celestial Coordinate Systems</primary>
+<secondary>Ecliptic Coordinates</secondary>
+<seealso>Ecliptic</seealso>
+</indexterm>
+<para>
+The Ecliptic coordinate system uses the <link
+linkend="ai-ecliptic">Ecliptic</link> for its Fundamental Plane.  The
+Ecliptic is the path that the Sun appears to follow across the sky over
+the course of a year.  It is also the projection of the Earth's
+orbital plane onto the Celestial Sphere.  The latitudinal angle is
+called the <firstterm>Ecliptic Latitude</firstterm>, and the longitudinal angle
+is called the <firstterm>Ecliptic Longitude</firstterm>.  Like Right Ascension
+in the Equatorial system, the zeropoint of the Ecliptic Longitude is the <link
+linkend="ai-equinox">Vernal Equinox</link>.
+</para><para>
+What do you think such a coordinate system would be useful for?  If you
+guessed charting solar system objects, you are right!  Each of the
+planets (except Pluto) orbits the Sun in roughly the same plane, so they always
+appear to be somewhere near the Ecliptic (&ie;, they always have small ecliptic
+latitudes).
+</para>
+</sect2>
+
+<sect2 id="galactic">
+<title>The Galactic Coordinate System</title>
+
+<indexterm><primary>Celestial Coordinate Systems</primary>
+<secondary>Galactic Coordinates</secondary>
+</indexterm>
+<para>
+<indexterm><primary>Milky Way</primary></indexterm>
+The Galactic coordinate system uses the <firstterm>Milky Way</firstterm> as its
+Fundamental Plane.  The latitudinal angle is called the <firstterm>Galactic
+Latitude</firstterm>, and the longitudinal angle is called the
+<firstterm>Galactic Longitude</firstterm>.  This coordinate system is useful for
+studying the Galaxy itself.  For example, you might want to know how the density
+of stars changes as a function of Galactic Latitude, to how much the disk of the
+Milky Way is flattened.
+</para>
+</sect2>
+</sect1>