Editing Second (section)

===Sexagesimal divisions of calendar time and day===
Civilizations in the classic period and earlier created divisions of the calendar as well as arcs using a sexagesimal system of counting, so at that time the second was a sexagesimal subdivision of the day (ancient second{{nbsp}}={{nbsp}}{{sfrac|day|60×60}}), not of the hour like the modern second (={{nbsp}}{{sfrac|hour|60×60}}).{{cn|date=November 2024}}  Sundials and water clocks were among the earliest timekeeping devices, and units of time were measured in degrees of arc.  Conceptual units of time smaller than realisable on sundials were also used.

There are references to "second" as part of a lunar month in the writings of natural philosophers of the Middle Ages, which were mathematical subdivisions that could not be measured mechanically.{{refn 
|In 1000, the [[Persian people|Persian]] scholar [[al-Biruni]], writing in Arabic, used the term ''second'', and defined the division of time between [[new moon]]s of certain specific weeks as a number of days, hours, minutes, seconds, thirds, and fourths after noon Sunday.<ref name="al-Biruni">{{cite book
 |author=Al-Biruni
 |year=1879
 |orig-year=1000
 |title=The chronology of ancient nations
 |url=https://books.google.com/books?id=pFIEAAAAIAAJ&pg=PA148
 |pages=147–149
 |translator-last=Sachau
 |translator-first=C. Edward
 |author-link=Al-Biruni
 |access-date=February 23, 2016
 |archive-url=https://web.archive.org/web/20190916000857/https://books.google.com/books?id=pFIEAAAAIAAJ&pg=PA148&hl=en#v=onepage&q=
 |archive-date=September 16, 2019
 |url-status=live
 }}</ref>|group=nb}}{{refn |In 1267, the medieval English scientist [[Roger Bacon]], writing in Latin, defined the division of time between [[full moon]]s as a number of hours, minutes, seconds, thirds, and fourths (''horae'', ''minuta'', ''secunda'', ''tertia'', and ''quarta'') after noon on specified calendar dates.<ref>
{{cite book
 |first=Roger |last=Bacon
 |year=2000 |orig-year=1267
 |title=The Opus Majus of Roger Bacon
 |publisher=[[University of Pennsylvania Press]]
 |page=table facing page 231
 |isbn=1-85506-856-7
 |no-pp=true
 |others=translated by Robert Belle Burke
}}</ref>|group=nb}}