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| {{numeral systems}}
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| '''Sexagesimal''' ('''base 60''') is a [[numeral system]] with [[60 (number)|sixty]] as its [[radix|base]]. It originated with the ancient [[Sumerians]] in the [[3rd millennium BC]], it was passed down to the ancient [[Babylonia]]ns, and it is still used — in a modified form — for measuring [[time]], [[angle]]s, and [[geographic coordinate system|geographic coordinates]].
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| The number 60, a [[highly composite number]], has twelve [[factorization|factors]], namely {{nowrap|{1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60}}}, of which 2, 3, and 5 are [[prime number]]s. With so many factors, many [[fraction (mathematics)|fraction]]s involving sexagesimal numbers are simplified. For example, one hour can be divided evenly into sections of 30 minutes, 20 minutes, 15 minutes, 12 minutes, 10 minutes, 6 minutes, 5 minutes, 4 minutes, 3 minutes, 2 minutes, and 1 minute. 60 is the smallest number that is divisible by every number from 1 to 6; that is, it is the [[lowest common multiple]] of 1, 2, 3, 4, 5, and 6.
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| ''In this article, all sexagesimal digits are represented as decimal numbers, except where otherwise noted. [For example, '''''10''''' means [[10 (number)|ten]] and '''''60''''' means [[60 (number)|sixty]].]''
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| ==Origin==
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| It is possible for people to [[Finger counting|count on their fingers]] to 12 using one hand only, with the thumb pointing to each [[Phalanx bone|finger bone]] on the four fingers in turn. A traditional counting system still in use in many regions of Asia works in this way, and could help to explain the occurrence of numeral systems based on 12 and 60 besides those based on 10, 20 and 5. In this system, the one (usually right) hand counts repeatedly to 12, displaying the number of iterations on the other (usually left), until five dozens, i. e. the 60, are full.<ref name=Ifrah>{{Citation
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| | last = Ifrah
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| | first = Georges
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| | author-link = Georges Ifrah
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| | title = The Universal History of Numbers: From prehistory to the invention of the computer.
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| | publisher = [[John Wiley and Sons]]
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| | year= 2000
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| | page =
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| | isbn = 0-471-39340-1
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| }}. Translated from the French by David Bellos, E.F. Harding, Sophie Wood and Ian Monk.</ref><ref name=Macey>{{cite book|last=Macey|first=Samuel L.|title=The Dynamics of Progress: Time, Method, and Measure|year=1989|publisher=University of Georgia Press|location=Atlanta, Georgia|isbn=978-0-8203-3796-8|pages=92|url=http://books.google.com/books?id=xlzCWmXguwsC&pg=PA92&lpg=PA92}}</ref>
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| According to [[Otto Neugebauer]], the origins of the sixty-count was through a count of three twenties. The precursor to the later six-ten alternation was through symbols for the sixths, (i.e. 1/6, 2/6, 3/6, 4/6, 5/6), coupled with decimal numbers, led to the same three-score count, and also to the division-system that the Sumerians were famous for. In normal use, numbers were a haphazard collection of units, tens, sixties, and hundreds. A number like 192, would be expressed uniformly in the tables as 3A2 (with A as the symbol for the '10') but would in the surrounding text be given as XIxxxii i.e., hundred (big 10), sixty (big 1), three tens (little 10's), two (little 1's).<ref name=Neugebauer>{{cite book|last=Neugebauer|first = O.|title=The Exact Sciences In Antiquity|publisher=Dover|year=1969|isbn=0-486-22332-9|pages=239}}{{page needed|reason=on Google Books, p239 is in the index|date=November 2012}}</ref>
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| ==Usage==
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| ===Babylonian mathematics===
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| The sexagesimal system as used in ancient [[Mesopotamia]] was not a pure base-60 system, in the sense that it did not use 60 distinct symbols for its [[numerical digit|digits]]. Instead, the [[cuneiform (script)|cuneiform]] digits used [[10 (number)|ten]] as a '''sub-base''' in the fashion of a [[sign-value notation]]: a sexagesimal digit was composed of a group of narrow, wedge-shaped marks representing units up to nine (Y, YY, YYY, YYYY, ... YYYYYYYYY) and a group of wide, wedge-shaped marks representing up to five tens (<, <<, <<<, <<<<, <<<<<). The value of the digit was the sum of the values of its component parts:
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| [[Image:Babylonian numerals.svg|470px|center]]
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| Numbers larger than 59 were indicated by multiple symbol blocks of this form in [[positional notation|place value notation]].
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| Because there was no symbol for [[0 (number)|zero]] in Sumerian or early Babylonian numbering systems, it is not always immediately obvious how a number should be interpreted, and its true value must sometimes have been determined by its context. Without context, this system was fairly ambiguous. For example, the symbols for 1 and 60 are identical{{Citation needed|reason=It's not clear how context would indicate a difference between 1 and 60 and it would be nice to have a source for the information|date=September 2013}}. Later Babylonian texts used a placeholder ([[File:Babylonian digit 0.svg]]) to represent zero, but only in the medial positions, and not on the right-hand side of the number, as we do in numbers like 13,200.
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| ===Other historical usages===
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| In the [[Chinese calendar]], a [[sexagenary cycle]] is commonly used, in which days or years are named by positions in a sequence of ten stems and in another sequence of 12 branches. The same stem and branch repeat every 60 steps through this cycle.
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| Book VIII of [[Plato]]'s [[The Republic (Plato)|Republic]] involves an allegory of marriage centered on the number 60<sup>4</sup> = 12,960,000 and its divisors. This number has the particularly simple sexagesimal representation 1,0,0,0,0. Later scholars have invoked both Babylonian mathematics and music theory in an attempt to explain this passage.<ref>{{citation
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| | last = Barton | first = George A.
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| | title = On the Babylonian origin of Plato's nuptial number
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| | year = 1908
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| | journal = Journal of the American Oriental Society
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| | volume = 29
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| | pages = 210–219
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| | doi = 10.2307/592627
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| | jstor = 592627}}. {{citation
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| | last = McClain |first = Ernest G.
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| | authorlink = Ernest G. McClain
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| | year = 1974
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| | title = Musical "Marriages" in Plato's "Republic"
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| | journal = Journal of Music Theory
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| | volume = 18
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| | issue = 2
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| | pages = 242–272
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| | doi = 10.2307/843638
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| | author2 = Plato,
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| | jstor = 843638}}</ref>
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| [[Ptolemy|Ptolemy's]] ''[[Almagest]]'', a treatise on [[mathematical astronomy]] written in the second century AD, uses base 60 to express the fractional parts of numbers. In particular, his [[table of chords]], which was essentially the only extensive [[trigonometric table]] for more than a millennium, has fractional parts in base 60.
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| In the late eighteenth and early nineteenth century [[Tamil people|Tamil]] astronomers were found to make astronomical calculations, reckoning with shells using a mixture of decimal and sexagesimal notations developed by [[Hellenistic#Indian reference|Hellenistic]] astronomers.<ref>{{citation
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| | title=Tamil Astronomy: A Study in the History of Astronomy in India
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| | first=Otto
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| | last=Neugebauer
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| | authorlink= Otto Neugebauer
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| | journal=Osiris
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| | volume=10
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| | pages=252–276
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| | year=1952
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| }}; reprinted in {{Citation
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| | first=Otto
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| | last=Neugebauer
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| | authorlink= Otto Neugebauer
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| | title = Astronomy and History: Selected Essays
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| | place = New York
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| | publisher = [[Springer-Verlag]]
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| | year = 1983
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| | isbn = 0-387-90844-7}}</ref>
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| Base-60 number systems have also been used in some other cultures that are unrelated to the Sumerians, for by example the Ekagi people of [[Western New Guinea]].<ref>{{citation
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| | title=Kapauku numeration: Reckoning, racism, scholarship, and Melanesian counting systems
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| | first=Nancy
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| | last=Bowers
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| | journal=Journal of the Polynesian Society
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| | volume=86
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| | issue=1
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| | pages=105–116.
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| | year=1977
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| | url=http://www.ethnomath.org/resources/bowers1977.pdf
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| }}</ref><ref>{{citation
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| | first = Glendon Angove
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| | last = Lean
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| | title = Counting Systems of Papua New Guinea and Oceania
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| | publisher = Ph.D. thesis, [[Papua New Guinea University of Technology]]
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| | year = 1992
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| | url = http://www.uog.ac.pg/glec/thesis/thesis.htm}}. See especially [http://www.uog.ac.pg/glec/thesis/ch4web/ch4.htm chapter 4].</ref>
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| ===Notation===
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| In [[Hellenistic Greece|Hellenistic Greek]] astronomical texts, such as the writings of [[Ptolemy]], sexagesimal numbers were written using the [[Greek numerals#Hellenistic zero|Greek alphabetic numerals]], with each sexagesimal digit being treated as a distinct number. The Greeks limited their use of sexagesimal numbers to the fractional part of a number and employed a variety of markers to indicate a zero.<ref>{{Citation |last= Aaboe |first= Asger |authorlink = Asger Aaboe |year= 1964 |title= Episodes from the Early History of Mathematics |series = New Mathematical Library |volume = 13 |publisher= Random House |publication-place= New York |pages= 103–104 |url= |accessdate= }}</ref>
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| In medieval Latin texts, sexagesimal numbers were written using [[Hindu Arabic numerals]]; the different levels of fractions were denoted ''minuta'' (i.e., fraction), ''minuta secunda'', ''minuta tertia'', etc. By the seventeenth century it became common to denote the integer part of sexagesimal numbers by a superscripted zero, and the various fractional parts by one or more accent marks. John Wallis, in his ''Mathesis universalis'', generalized this notation to include higher multiples of 60; giving as an example the number <nowiki>49````,36```,25``,15`,1°,15',25'',36''',49''''</nowiki>; where the numbers to the left are multiplied by higher powers of 60, the numbers to the right are divided by powers of 60, and the number marked with the superscripted zero is multiplied by 1.<ref>{{cite book | last = Cajori | first = Florian | authorlink = Florian Cajori | title = A History of Mathematical Notations | publisher = Cosimo, Inc. | volume = 1 | origyear = 1928 | year = 2007 | location = New York | page = 216 | url = http://books.google.com/books?id=OQZxHpG2y3UC&printsec=frontcover#v=onepage&q&f=false | isbn = 9781602066854 }}</ref> This notation leads to the modern signs for degrees, minutes, and seconds. The same minute and second nomenclature is also used for units of time, and the modern notation for time with hours, minutes, and seconds written in decimal and separated from each other by colons may be interpreted as a form of sexagesimal notation.
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| In modern studies of ancient mathematics and astronomy it is customary to write sexagesimal numbers with each sexagesimal digit represented in standard decimal notation as a number from 0 to 59, and with each digit separated by a comma. When appropriate, the fractional part of the sexagesimal number is separated from the whole number part by a semicolon rather than a comma, although in many cases this distinction may not appear in the original historical document and must be taken as an interpretation of the text.<ref>{{Citation | last = Neugebauer | first = Otto | author-link = Otto Neugebauer | last2 = Sachs | first2 = Abraham Joseph | author2-link = Abraham Sachs | last3 = Götze | first3 = Albrecht | title = Mathematical Cuneiform Texts | place = New Haven | publisher = American Oriental Society and the American Schools of Oriental Research | series = American Oriental Series | volume = 29 | year = 1945 | page = 2 | url = http://books.google.com/books?hl=en&lr=&id=i-juAAAAMAAJ&oi=fnd&pg=PA1&dq=%22sexagesimal+notation%22&ots=nkmW8KTnQ_&sig=U_K4iOoKy5Xf70UrbjoTyS3hN2A#v=onepage&q=%22sexagesimal%20notation%22&f=false}}</ref> Using this notation the square root of two, which in decimal notation appears as 1.41421... appears in modern sexagesimal notation as 1;24,51,10....<ref>{{harvtxt|Aaboe|1964}}, pp. 15–16, 25</ref> This notation is used in this article.
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| ===Modern usage===
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| Unlike most other numeral systems, sexagesimal is not used so much in modern times as a means for general computations, or in logic, but rather, it is used in measuring [[angle]]s, geographic coordinates, and [[time]].
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| One [[hour]] of time is divided into 60 [[minute]]s, and one minute is divided into 60 seconds. Thus, a measurement of time such as "3:23:17" (three hours, 23 minutes, and 17 seconds) can be interpreted as a sexagesimal number, meaning 3×60<sup>2</sup> + 23×60<sup>1</sup> + 17×60<sup>0</sup>. As with the ancient Babylonian sexagesimal system, however, each of the three sexagesimal digits in this number (3, 23, and 17) is written using the [[decimal]] system.
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| Similarly, the practical unit of angular measure is the [[degree (angle)|degree]], of which there are [[360 (number)|360]] in a circle. There are 60 [[minute of arc|minutes of arc]] in a degree, and 60 [[arcseconds]] in a minute.
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| In some usage systems, each position past the sexagesimal point was numbered, using Latin or French roots: ''prime'' or ''primus'', ''seconde'' or ''secundus'', ''tierce'', ''quatre'', ''quinte'', etc. To this day we call the second-order part [[second|of an hour]] or [[second of arc|of a degree]] a "second". Until at least the 18th century, 1/60 of a second was called a "tierce" or "third".<ref>{{citation|title=A natural history of vision|last=Wade|first=Nicholas|publisher=MIT Press|year=1998|isbn=978-0-262-73129-4|page=193}}</ref><ref>{{citation|title=Middle English Dictionary|first=Robert E.|last=Lewis|publisher=University of Michigan Press|year=1952|isbn=978-0-472-01212-1|page=231}}</ref>
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| == Fractions ==
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| In the sexagesimal system, any [[fraction (mathematics)|fraction]] in which the [[denominator]] is a [[regular number]] (having only 2, 3, and 5 in its [[prime factorization]]) may be expressed exactly.<ref>{{citation
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| | title=Astronomical Cuneiform Texts
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| | last=Neugebauer
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| | first=Otto E.
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| | author-link=Otto E. Neugebauer
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| | year=1955
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| | publisher=Lund Humphries
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| | place=London
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| }}</ref> The table below shows the sexagesimal representation of all fractions of this type in which the denominator is less than 60. The sexagesimal values in this table may be interpreted as giving the number of minutes and seconds in a given fraction of an hour; for instance, 1/9 of an hour is 6 minutes and 40 seconds. However, the representation of these fractions as sexagesimal numbers does not depend on such an interpretation.
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| {| class="wikitable" style="margin: 1em auto 1em auto"
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| |-
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| ! Fraction:
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| | 1/2 || 1/3 || 1/4 || 1/5 || 1/6 || 1/8 || 1/9 || 1/10
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| |-
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| !Sexagesimal:
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| | 30 || 20 || 15 || 12 || 10 || 7,30 || 6,40 || 6
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| |-
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| ! colspan="9" |
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| |-
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| ! Fraction:
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| | 1/12||1/15 || 1/16 || 1/18 || 1/20 || 1/24 || 1/25 || 1/27
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| |-
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| !Sexagesimal:
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| | 5 ||4 || 3,45 || 3,20 || 3 || 2,30 || 2,24 || 2,13,20
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| |-
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| ! colspan="9" |
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| |-
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| ! Fraction:
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| | 1/30|| 1/32 || 1/36 || 1/40 || 1/45 || 1/48 || 1/50 || 1/54
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| |-
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| !Sexagesimal:
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| | 2 || 1,52,30 || 1,40 || 1,30 || 1,20 || 1,15 || 1,12 || 1,6,40
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| |}
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| However numbers that are not regular form more complicated [[repeating fraction]]s. For example:
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| :1/7 = 0;8,34,17,8,34,17 ... (with the sequence of sexagesimal digits 8,34,17 repeating infinitely often).
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| The fact in [[arithmetic]] that the two numbers that are adjacent to '''60''', namely '''59''' and '''61''', are both prime numbers implies that simple repeating fractions that repeat with a period of one or two sexagesimal digits can only have 59 or 61 as their denominators, and that other non-regular primes have fractions that repeat with a longer period.
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| == Examples ==
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| [[Image:Ybc7289-bw.jpg|right|thumb|200px|Babylonian tablet YBC 7289 showing the sexagesimal number {{nowrap|1;24,51,10}} approximating [[square root of 2|√2]]]]
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| The [[square root of 2]], the length of the [[diagonal]] of a [[unit square]], was approximated by the Babylonians of the Old Babylonian Period (1900 BC – 1650 BC) as
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| :<math>1;24,51,10=1+\frac{24}{60}+\frac{51}{60^2}+\frac{10}{60^3}=\frac{30547}{21600}\approx 1.414212\ldots</math><ref>[http://it.stlawu.edu/%7Edmelvill/mesomath/tablets/YBC7289.html YBC 7289 clay tablet]</ref>
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| Because <math>\sqrt{2}</math> is an [[irrational number]], it cannot be expressed exactly in sexagesimal numbers, but its sexagesimal expansion does begin 1;24,51,10,7,46,6,4,44 ...
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| The length of the [[tropical year]] in [[Chaldea|Neo-Babylonian astronomy]] (see [[Hipparchus]]), 365.24579... days, can be expressed in sexagesimal as 6,5;14,44,51 (6×60 + 5 + 14/60 + 44/60<sup>2</sup> + 51/60<sup>3</sup>) days. The average length of a year in the [[Gregorian calendar]] is exactly 6,5;14,33 in the same notation because the values 14 and 33 were the first two values for the tropical year from the [[Alfonsine tables]], which were in sexagesimal notation.
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| The value of [[pi|π]] as used by the [[Ancient Greece|Greek]] mathematician and scientist [[Claudius Ptolemaeus]] ([[Ptolemy]]) was 3;8,30 = 3 + 8/60 + 30/60<sup>2</sup> = 377/120 ≈ 3.141666....<ref>{{Citation | editor-last = Toomer | editor-first = G. J. | editor-link = Gerald J. Toomer | year = 1984 | title = Ptolemy's Almagest | publisher = Springer Verlag | place = New York | page = 302 | isbn = 0-387-91220-7 | url = | accessdate = }}</ref> [[Jamshīd al-Kāshī]], a 15th-century [[Persia]]n mathematician, calculated π in sexagesimal numbers to an accuracy of nine sexagesimal digits; his value for 2π was 6;16,59,28,1,34,51,46,14,50.<ref>{{citation|contribution=Al-Kashi|first=Adolf P.|last=Youschkevitch|editor-first=Boris A.|editor-last=Rosenfeld|page=256|title=[[Dictionary of Scientific Biography]]}}.</ref><ref>{{harvtxt|Aaboe|1964}}, p. 125</ref>
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| ==See also==
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| * [[Latitude]]
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| * [[Trigonometry]]
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| ==References==
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| {{reflist|colwidth=30em}}
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| ==Additional reading==
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| *{{citation
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| | first = Georges
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| | last = Ifrah
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| | title = The Universal History of Numbers: From Prehistory to the Invention of the Computer
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| | publisher = Wiley
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| | year = 1999
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| | isbn = 0-471-37568-3}}.
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| *{{citation
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| | first1 = Hans J.
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| | last1 = Nissen
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| | first2 = P.
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| | last2 = Damerow
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| | first3 = R.
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| | last3 = Englund
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| | title = Archaic Bookkeeping
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| | publisher = University of Chicago Press
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| | year = 1993
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| | isbn = 0-226-58659-6}}
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| ==External links==
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| *[http://www.wdl.org/en/item/4259 "Facts on the Calculation of Degrees and Minutes"] is an Arabic language book by [[Sibt al-Maridini|Sibṭ al-Māridīnī, Badr al-Dīn Muḥammad ibn Muḥammad]] (b. 1423). This work offers a very detailed treatment of sexagesimal mathematics and includes what appears to be the first mention of the periodicity of sexagesimal fractions.
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| [[Category:Positional numeral systems]]
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| [[Category:Babylonian mathematics]]
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