Alpha (uppercase Α, lowercase α; Ancient Greek : άλφα, álpha, modern pronunciation álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of 1.

It was derived from the Phoenician and Hebrew letter aleph - an ox or leader. ^[undefined]

Letters that arose from alpha include the Latin A and the Cyrillic letter �.

In English, the noun "alpha" is used as a synonym for "beginning", or "first" (in a series), reflecting its Greek roots.

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In Ancient Greek, alpha was pronounced [ a ] and could be either phonemically long ([a:]) or short ([a]). Where there is ambiguity, long and short alpha are sometimes written with a macron and breve today: Ᾱᾱ, Ᾰᾰ.

In Modern Greek, vowel length has been lost, and all instances of alpha simply represent [a].

In the polytonic orthography of Greek, alpha, like other vowel letters, can occur with several diacritic marks: any of three accent symbols ( ά, ὰ, ᾶ ), and either of two breathing marks ( �, ἀ ), as well as combinations of these. It can also combine with the iota subscript ( ᾳ ).

In the Attic-Ionic dialect of Ancient Greek, long alpha [a�] fronted to [ ɛ� ] (eta). In Ionic, the shift took place in all positions. In Attic, the shift did not take place after epsilon, iota, and rho (ε, ι, �; e, i, r). In Doric and Aeolic, long alpha is preserved in all positions. ^[undefined]

Privative a is the Ancient Greek prefix ἀ- or ἀν-a-, an-, added to words to negate them. It originates from the Proto-Indo-European ** n̥-* (syllabic nasal) and is cognate with English un-.

Copulative a is the Greek prefix �- or ἀ-ha-, a-. It comes from Proto-Indo-European ** sm̥*.

The letter alpha represents various concepts in physics and chemistry, including alpha radiation, angular acceleration, alpha particles, alpha carbon and strength of electromagnetic interaction (as Fine-structure constant). Alpha also stands for thermal expansion coefficient of a compound in physical chemistry. It is also commonly used in mathematics in algebraic solutions representing quantities such as angles. Furthermore, in mathematics, the letter alpha is used to denote the area underneath a normal curve in statistics to denote significance level ^[undefined] when proving null and alternative hypotheses. In zoology, it is used to name the dominant individual in a wolf or dog pack.

The proportionality operator "�" (in Unicode : U+221D) is sometimes mistaken for alpha.

The uppercase letter alpha is not generally used as a symbol because it tends to be rendered identically to the uppercase Latin A.

In the International Phonetic Alphabet, the letter É‘, which looks similar to the lower-case alpha, represents the open back unrounded vowel.

Alpha was derived from aleph , which in Phoenician means "ox". ^[undefined]

Plutarch, in Moralia , ^[undefined] presents a discussion on why the letter alpha stands first in the alphabet. Ammonius asks Plutarch what he, being a Boeotian, has to say for Cadmus, the Phoenician who reputedly settled in Thebes and introduced the alphabet to Greece, placing alpha first because it is the Phoenician name for ox —which, unlike Hesiod, ^[undefined] the Phoenicians considered not the second or third, but the first of all necessities. "Nothing at all," Plutarch replied. He then added that he would rather be assisted by Lamprias, his own grandfather, than by Dionysus' grandfather, i.e. Cadmus. For Lamprias had said that the first articulate sound made is "alpha", because it is very plain and simple—the air coming off the mouth does not require any motion of the tongue—and therefore this is the first sound that children make.

According to Plutarch's natural order of attribution of the vowels to the planets, alpha was connected with the Moon.

Alpha, both as a symbol and term, is used to refer to or describe a variety of things, including the first or most significant occurrence of something.

The New Testament has God declaring himself to be the "Alpha and Omega, the beginning and the end, the first and the last." (Revelation 22:13, KJV, and see also 1:8).

The term "alpha" has been used to denote position in social hierarchy, examples being "alpha males" or pack leaders.

For accented Greek characters, see Greek diacritics: Computer encoding.