Editing 5th millennium BC (section)

==Calendars and chronology==
The 5th millennium has become a start point for calendars and chronologies. The year 4750 BC is the retrospective startpoint for the [[Assyrian calendar]], marking the traditional date for the foundation of [[Assur]], some 2,000 years before it actually happened.<ref>{{Cite book |url=https://www.academia.edu/7933079 |chapter=Far from Aram-Nahrin: The Suryoye Diaspora Experience |title=Border Terrains: World Diasporas in the 21st Century |first=Marta |last=Wozniak |editor-first=Allyson |editor-last=Eamer |publisher=Inter-Disciplinary Press, Oxford |year=2012 |isbn=978-1-84888-117-4 |page=78}}</ref>

Another traditional date is 19 July 4241 BC, marking the supposed beginning of the [[Egyptian calendar]], as calculated retrospectively by [[Eduard Meyer]]. The more likely startpoint is 19 July 2781 BC, one [[Sothic cycle]] later. It has generally been believed that the calendar was based on a heliacal (dawn) rising of [[Sirius]] but that view is now being questioned.<ref>{{cite book |last=Grimal |first=Nicolas |title=A History of Ancient Egypt |page=52 |publisher=Librairie Arthéme Fayard |year=1988}}</ref><ref>{{cite journal |last=Kitchen |first=K. A. |title=The Chronology of Ancient Egypt |page=205 |journal=World Archaeology |volume=23 |issue=2 |date=October 1991|doi=10.1080/00438243.1991.9980172 }}</ref>

According to the [[Ussher chronology]], the creation of Earth happened on 22/23 October 4004 BC. This chronology was the work of [[James Ussher]], whose basis was the dates in the [[Old Testament]] of the [[Bible]]. He estimated that the [[universe]] was created by [[God]] at either 18:00 on the 22nd (Jewish calendar) or 09:00 on the 23rd (Ussher-Lightfoot-Chronology).<ref>{{cite journal |url=https://blogs.scientificamerican.com/history-of-geology/october-23-4004-bc-happy-birthday-earth/ |title=October 23, 4004 B.C.: Happy Birthday Earth! |author=Bressan, David |journal=History of Geology |publisher=Scientific American |date=22 October 2013 |access-date=2 November 2019}}</ref>

Yet another calendar starting date in the 5th millennium is Monday, 1 January 4713 BC, the beginning of the current [[Julian Period]], first described by [[Joseph Justus Scaliger]] in the sixteenth century. This Julian Period lasts 7,980 years until the year 3268 (current era) in the next millennium. It is a useful device for date conversions between different calendars. The date of origin has the integer value of zero in the Julian Day Count: i.e., in the [[Julian Calendar]]; the equivalent date in the [[Gregorian Calendar]] is 24 November 4714&nbsp;BC.<ref>{{cite book |chapter=Introduction to Positional Astronomy |last=Seidelmann |first=P. Kenneth |year=2013 |title=Explanatory Supplement to the Astronomical Almanac |edition=3rd |page=15 |publisher=University Science Books |isbn=978-1-891389-85-6}}</ref>