It is central to many systems of timekeeping, including the Western calendar and units of time of day, and frequently appears in the world's major religions.
As with eleven,<ref name="oedgoesto">Oxford English Dictionary, 1st ed. "eleven, adj. and n." Oxford University Press (Oxford), 1891.</ref> the earliest forms of twelve are often considered to be connected with Proto-Germanic Template:Lang or Template:Lang ("to leave"), with the implicit meaning that "two is left" after having already counted to ten.<ref name="oed">Oxford English Dictionary, 1st ed. "twelve, adj. and n." Oxford University Press (Oxford), 1916.</ref> The Lithuanian suffix is also considered to share a similar development.<ref name="oed" /> The suffix Template:Lang has also been connected with reconstructions of the Proto-Germanic for ten.<ref name="oedgoesto"/><ref>Template:Citation.</ref>
As mentioned above, 12 has its own name in Germanic languages such as English (dozen), Dutch (Template:Lang), German (Template:Lang), and Swedish (Template:Lang), all derived from Old French Template:Lang. It is a compound number in many other languages, e.g. Italian Template:Lang (but in Spanish and Portuguese, 16, and in French, 17 is the first compound number),{{ safesubst:#invoke:Unsubst||date=__DATE__ |$B=
Template:Fix
}} Japanese 十二 jūni.Template:Clarify
Written representation
In prose writing, twelve, being the last single-syllable numeral, is sometimes taken as the last number to be written as a word, and 13 the first to be written using digits.
This is not a binding rule, and in English language tradition, it is sometimes recommended to spell out numbers up to and including either nine, ten or twelve, or even ninety-nine or one hundred. Another system spells out all numbers written in one or two words (sixteen, twenty-seven, fifteen thousand, but 372 or 15,001).<ref>Template:Cite web</ref>
In German orthography, there used to be the widely followed (but unofficial) rule of spelling out numbers up to twelve (zwölf). The DudenTemplate:Year needed (the German standard dictionary) mentions this rule as outdated.
The cubic close packing and hexagonal close packing, which are the two densest possible sphere packings in three-dimensional space (the Kepler conjecture, proved by Thomas Hales), both have each sphere touching twelve other spheres. Twelve is also the kissing number in three dimensions.
Twelve is the smallest weight for which a cusp form exists. This cusp form is the discriminant <math>\Delta(q)</math> whose Fourier coefficients are given by the Ramanujan <math>\tau</math>-function and which is (up to a constant multiplier) the 24th power of the Dedekind eta function:
This fact is related to a constellation of interesting appearances of the number twelve in mathematics ranging from the fact that the abelianization of special linear group <math>\operatorname{SL}(2,\mathrm {Z})</math> has twelve elements, to the value of the Riemann zeta function at <math>-1</math> being <math>-\tfrac {1}{12}</math>, which stems from the Ramanujan summation
The number twelve carries religious, mythological and magical symbolism; since antiquity, the number has generally represented perfection, entirety, or cosmic order.Template:Sfnp
The number 12 is notable within the Hebrew Bible, and in Christianity:
IshmaelTemplate:Mdashthe first-born son of AbrahamTemplate:Mdashhas 12 sons/princes (Genesis 25:16), and Jacob also has 12 sons, who are the progenitors of the Twelve Tribes of Israel.<ref>"And it is thought that there is a special significance in the number twelve. It was typified, we know, by many things in the Old Testament; by the twelve sons of Jacob, by the twelve princes of the children of Israel, by the twelve fountains in Elim, by the twelve stones in Aaron's breast-plate, by the twelve loaves of the shew-bread, by the twelve spies sent by Moses, by the twelve stones of which the altar was made, by the twelve stones taken out of Jordan, by the twelve oxen which bare"
P. Young, Daily readings for a year (1863), p. 150.
</ref> This is reflected in Christian tradition, notably in the twelve Apostles. When Judas Iscariot is disgraced, a meeting is held (Acts) to add Saint Matthias to complete the number twelve once more.
The Book of Revelation contains much numerical symbolism, and many of the numbers mentioned have 12 as a divisor. Template:Bibleverse-nb mentions a woman—interpreted as the people of Israel, the Church and the Virgin Mary—wearing a crown of twelve stars (representing each of the twelve tribes of Israel). Furthermore, there are 12,000 people sealed from each of the twelve tribes of Israel (the Tribe of Dan is omitted while Manasseh is mentioned), making a total of 144,000 (which is the square of 12 multiplied by a thousand).
The Chinese use a 12-year cycle for time-reckoning called Earthly Branches.
There are twelve hours in a half day, numbered one to twelve for both the ante meridiem (a.m.) and the post meridiem (p.m.). 12:00 p.m. is midday or noon, and 12:00 a.m. is midnight.
The basic units of time (60 seconds, 60 minutes, 24 hours) are evenly divisible by twelve into smaller units.
In rugby league, one of the starting second-row forwards wears the number 12 jersey in most competitions. An exception is in the Super League, which uses static squad numbering.
In rugby union, one of the starting centres, most often but not always the inside centre, wears the 12 shirt.
Twelve is the number of pitch classes in an octave, not counting the duplicated (octave) pitch. Also, the total number of major keys, (not counting enharmonic equivalents) and the total number of minor keys (also not counting equivalents). This applies only to twelve tone equal temperament, the most common tuning used today in western influenced music.
The twelfth is the interval of an octave and a fifth. Instruments such as the clarinet which behave as a stopped cylindrical pipe overblow at the twelfth.
The twelve-bar blues is one of the most prominent chord progressions in popular music.
Art theory
There are twelve basic hues in the color wheel: three primary colors (red, yellow, blue), three secondary colors (orange, green, purple) and six tertiary colors (names for these vary, but are intermediates between the primaries and secondaries).
