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<sect2 id="calc-apcoords">
<title>Apparent Coordinates module</title>
<indexterm><primary>Tools</primary>
<secondary>Astrocalculator</secondary>
<tertiary>Apparent Coordinates module</tertiary>
</indexterm>
<screenshot>
<screeninfo>
The Apparent Coordinates calculator module
</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="calc-apcoords.png" format="PNG"/>
</imageobject>
<textobject>
<phrase>Apparent Coordinates</phrase>
</textobject>
</mediaobject>
</screenshot>
<para>
The Apparent Coordinates module converts the <firstterm>catalog
coordinates</firstterm> of a point in the sky to its
<firstterm>apparent coordinates</firstterm> for any date. The
coordinates of objects in the sky are not fixed, because of
<link linkend="ai-precession">precession</link>, nutation and
aberration. This module takes these effects into account.
</para>
<para>
To use the module, first enter the desired target date and time
in the <guilabel>Target Time/Date</guilabel> section. Then,
enter the catalog coordinates in the <guilabel>Catalog
Coordinates</guilabel> section. You can also specify the
catalog's epoch here (usually 2000.0 for modern object
catalogs). Finally, press the <guibutton>Compute</guibutton>
button, and the object's coordinates for the target date
will be displayed in the <guilabel>Apparent Coordinates</guilabel>
section.
</para>
</sect2>
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