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diff --git a/doc/kstars/hourangle.docbook b/doc/kstars/hourangle.docbook new file mode 100644 index 00000000..fc327446 --- /dev/null +++ b/doc/kstars/hourangle.docbook @@ -0,0 +1,33 @@ +<sect1 id="ai-hourangle"> +<sect1info> +<author> +<firstname>Jason</firstname> +<surname>Harris</surname> +</author> +</sect1info> +<title>Hour Angle</title> +<indexterm><primary>Hour Angle</primary> +<seealso>Local Meridian</seealso> +<seealso>Sidereal Time</seealso> +</indexterm> +<para> +As explained in the <link linkend="ai-sidereal">Sidereal Time</link> article, +the <firstterm>Right Ascension</firstterm> of an object indicates the Sidereal +Time at which it will transit across your <link linkend="ai-meridian">Local +Meridian</link>. An object's <firstterm>Hour Angle</firstterm> is +defined as the difference between the current Local Sidereal Time and the Right +Ascension of the object: +</para><para> +<abbrev>HA</abbrev><subscript>obj</subscript> = +<abbrev>LST</abbrev> - <abbrev>RA</abbrev><subscript>obj</subscript> +</para><para> +Thus, the object's Hour Angle indicates how much Sidereal Time has passed +since the object was on the Local Meridian. It is also the angular distance +between the object and the meridian, measured in hours (1 hour = 15 degrees). +For example, if an object has an hour angle of 2.5 hours, it transited across +the Local Meridian 2.5 hours ago, and is currently 37.5 degrees West of the +Meridian. Negative Hour Angles indicate the time until the +<emphasis>next</emphasis> transit across the Local Meridian. Of course, an Hour +Angle of zero means the object is currently on the Local Meridian. +</para> +</sect1> |