8 ( eight) is the natural number following 7 and preceding 9.
Etymology
English
eight, from Old English eahta
, æhta,
Proto-Germanic *ahto is a direct continuation of Proto-Indo-European
*oḱtṓ-, and as such cognate with Greek ὀκτώ and Latin octo-, both of which stems are reflected by the English prefix
oct-, as in the ordinal adjective
octaval or
octavary, the distributive adjective is
octonary.
The adjective
octuple (Latin octu-plus) may also be used as a noun, meaning "a set of eight items"; the diminutive
octuplet is mostly used to refer to eight siblings delivered in one birth.
The Semitic numerals is based on a root *θmn-, whence Akkadian smn-, Arabic ṯmn-, Hebrew šmn- etc.
The Chinese numeral, written 八 (Mandarin: bā; Cantonese: baat), is from Old Chinese *priāt-, ultimately from Sino-Tibetan b-r-gyat or b-g-ryat which also yielded Tibetan brgyat.
It has been argued that, as the cardinal number is the highest number of items that can universally be cognitively processed as a single set, the etymology of the numeral eight might be the first to be considered composite, either as "twice four" or as "two short of ten", or similar.
The Turkic languages words for "eight" are from a Proto-Turkic stem *sekiz, which has been suggested as originating as a negation of eki "two", as in "without two fingers" (i.e., "two short of ten; two fingers are not being held up");[ Etymological Dictionary of Turkic Languages: Common Turkic and Interturkic stems starting with letters «L», «M», «N», «P», «S», Vostochnaja Literatura RAS, 2003, 241f. ( altaica.ru )]
this same principle is found in Finnic languages *kakte-ksa, which conveys a meaning of "two before (ten)". The Proto-Indo-European reconstruction *oḱtṓ- itself has been argued as representing an old dual, which would correspond to an original meaning of "twice four".
Proponents of this "quaternary hypothesis" adduce the numeral , which might be built on the stem new-, meaning "new" (indicating the beginning of a "new set of numerals" after having counted to eight).[the hypothesis is discussed critically (and rejected as "without sufficient support") by
Werner Winter, 'Some thought about Indo-European numerals' in: Jadranka Gvozdanović (ed.),
Indo-European Numerals, Walter de Gruyter, 1992, 14f.]
Evolution of the Arabic digit
The modern digit 8, like all modern
Arabic numerals other than zero, originates with the
Brahmi numerals.
The Brahmi digit for
eight by the 1st century was written in one stroke as a curve └┐ looking like an uppercase H with the bottom half of the left line and the upper half of the right line removed.
However, the digit for eight used in India in the early centuries of the Common Era developed considerable graphic variation, and in some cases took the shape of a single wedge, which was adopted into the Perso-Arabic tradition as
٨ (and also gave rise to the later Devanagari form
८); the alternative curved glyph also existed as a variant in Perso-Arabic tradition, where it came to look similar to our digit 5.
The digits as used in Al-Andalus by the 10th century were a distinctive western variant of the glyphs used in the Arabic-speaking world, known as ghubār numerals ( ghubār translating to "sand table"). In these digits, the line of the 5-like glyph used in Indian manuscripts for eight came to be formed in ghubār as a closed loop, which was the 8-shape that became adopted into European use in the 10th century.[Georges Ifrah, The Universal History of Numbers: From Prehistory to the Invention of the Computer transl. David Bellos et al. London: The Harvill Press (1998): 395, Fig. 24.68.]
Just as in most modern , in typefaces with text figures the character for the digit 8 usually has an ascender, as, for example, in .
The infinity symbol ∞, described as a "sideways figure eight", is unrelated to the digit 8 in origin; it is first used (in the mathematical meaning "infinity") in the 17th century, and it may be derived from the Roman numeral for "one thousand" CIƆ, or alternatively from the final Greek letter, ω.
In mathematics
8 is a
composite number and the first number which is neither
Prime number nor
semiprime. By Mihăilescu's Theorem, it is the only nonzero
perfect power that is one less than another perfect power. 8 is the first proper
Leyland number of the form , where in its case and both equal 2.
8 is a
Fibonacci number and the only nontrivial Fibonacci number that is a
perfect cube.
[Bryan Bunch, The Kingdom of Infinite Number. New York: W. H. Freeman & Company (2000): 88] always have exactly eight divisors.
8 is the base of the
octal number system.
Geometry
A
polygon with eight sides is an
octagon.
A regular octagon can fill a plane-vertex with a regular
triangle and a regular
icositetragon, as well as
tessellation two-dimensional space alongside squares in the truncated square tiling. This tiling is one of eight Archimedean tilings that are semi-regular, or made of more than one type of regular
polygon, and the only tiling that can admit a regular octagon.
The Ammann–Beenker tiling is a nonperiodic tesselation of
that feature prominent octagonal
silver eightfold symmetry, that is the two-dimensional orthographic projection of the four-dimensional 8-8 duoprism.
An octahedron is a regular polyhedron with eight equilateral triangles as faces. is the dual polyhedron to the cube and one of eight Deltahedron.
Vector spaces
The
are a hypercomplex normed division algebra that are an extension of the
. They are a double cover of special orthogonal group SO(8). The special unitary group SO(3) has an eight-dimensional adjoint representation whose colors are ascribed gauge symmetries that represent the vectors of the eight
in the
Standard Model.
display a periodicity of 8.
Group theory
The Lie group
E8 is one of 5 exceptional Lie groups.
The order of the smallest non-abelian group whose subgroups are all normal is 8.
List of basic calculations
|
|
| 8 × x | 8 | 16 | 24 | 32 | 40 | 48 | 56 | 64 | 72 | 80 | 88 | 96 | 104 | 112 | 120 |
|
|
| 8 ÷ x | 8 | 4 | 2. | 2 | 1.6 | 1. | 1. | 1 | 0. | 0.8
! | 0. | 0. | 0. | 0. | 0.5 |
| x ÷ 8 | 0.125 | 0.25 | 0.375 | 0.5 | 0.625 | 0.75 | 0.875 | 1 | 1.125 | 1.25
! | 1.375 | 1.5 | 1.625 | 1.75 | 1.875 |
|
|
| 8 | 8 | 64 | 512 | 4096 | 32768 | 262144 | 2097152 | 16777216 | 134217728 | 1073741824
! | 8589934592 | 68719476736 | 549755813888 |
| x | 1 | 256 | 6561 | 65536 | 390625 | 1679616 | 5764801 | 16777216 | 43046721 | 100000000
! | 214358881 | 429981696 | 815730721 |
In science
Physics
-
In nuclear physics, the second magic number.
Chemistry
-
The most stable allotrope of a sulfur molecule is made of eight sulfur atoms arranged in a rhombic form.
In technology
In culture
Currency
-
Sailors and civilians alike from the 1500s onward referred to evenly divided parts of the Spanish dollar as "pieces of eight", or "bits".
In religion, folk belief and divination
Buddhism
In general, "eight" seems to be an auspicious number for Buddhists. The
Dharmacakra, a
Buddhism symbol, has eight spokes.
The Buddha's principal teaching—the Four Noble Truths—ramifies as the Noble Eightfold Path and the Buddha emphasizes the importance of the eight attainments or jhanas.
Islam
-
The octagram Rub el Hizb is often used in Islamic symbology.
As a lucky number
-
The number eight is considered to be a lucky number in Chinese and other Asian cultures.
-
In Pythagorean numerology the number 8 represents victory, prosperity and overcoming.
-
hachi, ya is also considered a lucky number in Japan, but the reason is different from that in Chinese culture.
-
The Japanese thought of ya as a holy number in the ancient times. The reason is less well-understood, but it is thought that it is related to the fact they used eight to express large numbers vaguely such as Yae Hatae (literally, eightfold and twentyfold), Yakumo (literally, eight clouds), Yaoyorozu no Kami (literally, eight millions of Gods), etc. It is also guessed that the ancient Japanese gave importance to pairs, so some researchers guess twice as yo, which is also guessed to be a holy number in those times because it indicates the world (north, south, east, and west) might be considered a very holy number.
-
In numerology, 8 is the number of building, and in some theories, also the number of destruction.
In astrology
-
In the Middle Ages, 8 was the number of "unmoving" stars in the sky, and symbolized the perfection of incoming planetary energy.
In sports and other games
-
In association football, the number 8 has historically been the number of the Central Midfielder.
-
In baseball:
-
The center fielder is designated as number 8 for scorekeeping purposes.
-
In rugby league:
-
Most competitions (though not the Super League, which uses static squad numbering) use a position-based player numbering system in which one of the two starting props wears the number 8.
-
In the 2008 Games of the XXIX Olympiad held in Beijing, the official opening was on 08/08/08 at 8:08:08 p.m. CST.
In literature
-
In Terry Pratchett's Discworld series, eight is a magical number
In slang
-
An "eighth" is a common measurement of marijuana, meaning an eighth of an ounce. It is also a common unit of sale for psilocybin mushrooms.
-
In Colombia and Venezuela, "volverse un ocho" (meaning to tie oneself in a figure 8) refers to getting in trouble or contradicting oneself.
-
In China, "8" is used in chat speak as a term for parting. This is due to the closeness in pronunciation of "8" (bā) and the English word "bye".
Other uses
-
A figure 8 is the common name of a geometry shape, often used in the context of sports, such as skating.
External links
