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0001 <sect2 id="calc-julian">
0002 <title>Julian Day module</title>
0003 <indexterm><primary>Tools</primary>
0004 <secondary>Astrocalculator</secondary>
0005 <tertiary>Julian Day module</tertiary>
0006 </indexterm>
0008 <screenshot>
0009 <screeninfo>
0010 The Julian Day calculator module
0011 </screeninfo>
0012 <mediaobject>
0013   <imageobject>
0014     <imagedata fileref="calc-julian.png" format="PNG"/>
0015   </imageobject>
0016   <textobject>
0017     <phrase>Julian Day</phrase>
0018   </textobject>
0019 </mediaobject>
0020 </screenshot>
0022 <para>
0023 This module converts between the calendar <guilabel>Date and time:</guilabel>, the <link
0024 linkend="ai-julianday"><guilabel>Julian day:</guilabel></link>, and the
0025 <guilabel>Modified julian day:</guilabel>.  The Modified Julian Day
0026 is simply equal to the Julian Day - 2,400,000.5.
0027 </para><para>
0028 To use the module, enter one of the three dates and the corresponding values for
0029 the other two date systems will be displayed. You can also set the Date and time to now, by pressing
0030 the <guibutton>Now</guibutton> button.
0031 </para>
0033 <para>
0034 There is a batch mode for this module.  To use it, simply
0035 generate an input file whose lines each contain a number of values for
0036 the input parameter: <quote>Date and time</quote>, <quote>Julian day</quote>
0037 or <quote>Modified Julian day</quote>.
0038 Then specify the input and output filenames, and press the
0039 <guibutton>Compute</guibutton> button to generate the output
0040 file. The output file will contains values for the other two complementary parameters. For example,
0041 if your input file contains a set of <guilabel>Date and time:</guilabel> values, then each line of
0042 the output file will contain values for <guilabel>Julian day:</guilabel> and <guilabel>Modified julian day:</guilabel>.
0043 You can read the output directly in &kstars;
0044 by pressing the <guibutton>View output...</guibutton> button.
0045 </para>
0047 <tip>
0048 <para>Exercise:</para>
0049 <para>
0050 What calendar date does MJD = 0.0 correspond to?
0051 </para>
0052 </tip>
0054 </sect2>