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diff --git a/doc/kstars/equinox.docbook b/doc/kstars/equinox.docbook new file mode 100644 index 00000000..6d98ccc6 --- /dev/null +++ b/doc/kstars/equinox.docbook @@ -0,0 +1,37 @@ +<sect1 id="ai-equinox"> +<sect1info> +<author> +<firstname>Jason</firstname> +<surname>Harris</surname> +</author> +</sect1info> +<title>The Equinoxes</title> +<indexterm><primary>Equinoxes</primary> +<seealso>Celestial Equator</seealso> +<seealso>Ecliptic</seealso> +</indexterm> +<para> +Most people know the Vernal and Autumnal Equinoxes as +calendar dates, signifying the beginning of the Northern hemisphere's Spring +and Autumn, respectively. Did you know that the equinoxes are also positions in +the sky? +</para><para> +The <link linkend="ai-cequator">Celestial Equator</link> and the +<link linkend="ai-ecliptic">Ecliptic</link> are two +<link linkend="ai-greatcircle">Great Circles</link> on the +<link linkend="ai-csphere">Celestial Sphere</link>, set at an angle of 23.5 +degrees. The two points where they intersect are called the +<firstterm>Equinoxes</firstterm>. The <firstterm>Vernal Equinox</firstterm> +has coordinates RA=0.0 hours, Dec=0.0 degrees. The <firstterm>Autumnal +Equinox</firstterm> has coordinates RA=12.0 hours, Dec=0.0 degrees. +</para><para> +The Equinoxes are important for marking the seasons. Because they are on +the <link linkend="ai-ecliptic">Ecliptic</link>, the Sun passes through each +equinox every year. When the Sun passes through the Vernal Equinox (usually on +March 21st), it crosses the <link linkend="ai-cequator">Celestial Equator</link> +from South to North, signifying the end of Winter for the Northern hemisphere. +Similarly, whenthe Sun passes through the Autumnal Equinox (usually on September +21st), it crosses the Celestial Equator from North to South, signifying the +end of Winter for the Southern hemisphere. +</para> +</sect1> |