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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>B.7. Julian Dates</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="datetime-units-history.html" title="B.6. History of Units" /><link rel="next" href="sql-keywords-appendix.html" title="Appendix C. SQL Key Words" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">B.7. Julian Dates</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="datetime-units-history.html" title="B.6. History of Units">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="datetime-appendix.html" title="Appendix B. Date/Time Support">Up</a></td><th width="60%" align="center">Appendix B. Date/Time Support</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-keywords-appendix.html" title="Appendix C. SQL Key Words">Next</a></td></tr></table><hr /></div><div class="sect1" id="DATETIME-JULIAN-DATES"><div class="titlepage"><div><div><h2 class="title" style="clear: both">B.7. Julian Dates <a href="#DATETIME-JULIAN-DATES" class="id_link">#</a></h2></div></div></div><a id="id-1.11.3.10.2" class="indexterm"></a><p>3   The <em class="firstterm">Julian Date</em> system is a method for4   numbering days.  It is5   unrelated to the Julian calendar, though it is confusingly6   named similarly to that calendar.7   The Julian Date system was invented by the French scholar8   Joseph Justus Scaliger (1540–1609)9   and probably takes its name from Scaliger's father,10   the Italian scholar Julius Caesar Scaliger (1484–1558).11  </p><p>12   In the Julian Date system, each day has a sequential number, starting13   from JD 0 (which is sometimes called <span class="emphasis"><em>the</em></span> Julian Date).14   JD 0 corresponds to 1 January 4713 BC in the Julian calendar, or15   24 November 4714 BC in the Gregorian calendar.  Julian Date counting16   is most often used by astronomers for labeling their nightly observations,17   and therefore a date runs from noon UTC to the next noon UTC, rather than18   from midnight to midnight: JD 0 designates the 24 hours from noon UTC on19   24 November 4714 BC to noon UTC on 25 November 4714 BC.20  </p><p>21   Although <span class="productname">PostgreSQL</span> supports Julian Date notation for22   input and output of dates (and also uses Julian dates for some internal23   datetime calculations), it does not observe the nicety of having dates24   run from noon to noon.  <span class="productname">PostgreSQL</span> treats a Julian Date25   as running from local midnight to local midnight, the same as a normal26   date.27  </p><p>28   This definition does, however, provide a way to obtain the astronomical29   definition when you need it: do the arithmetic in time30   zone <code class="literal">UTC+12</code>.  For example,31</p><pre class="programlisting">32=&gt; SELECT extract(julian from '2021-06-23 7:00:00-04'::timestamptz at time zone 'UTC+12');33           extract34------------------------------35 2459388.9583333333333333333336(1 row)37=&gt; SELECT extract(julian from '2021-06-23 8:00:00-04'::timestamptz at time zone 'UTC+12');38               extract39--------------------------------------40 2459389.000000000000000000000000000041(1 row)42=&gt; SELECT extract(julian from date '2021-06-23');43 extract44---------45 245938946(1 row)47</pre><p>48  </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="datetime-units-history.html" title="B.6. History of Units">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="datetime-appendix.html" title="Appendix B. Date/Time Support">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-keywords-appendix.html" title="Appendix C. SQL Key Words">Next</a></td></tr><tr><td width="40%" align="left" valign="top">B.6. History of Units </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Appendix C. <acronym class="acronym">SQL</acronym> Key Words</td></tr></table></div></body></html>