<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>