A (disambiguation)

A is the first letter of the Latin alphabet. It can also refer to the following: In the sciences:

• A whitish-blue class of stars in the Morgan-Keenan system in astronomy.
• A January 1 through 15 discovery, in the provisional designation of a comet (for example, C/1760 A1, the Great Comet of 1760) or asteroid (for example, (4099) 1988 AB₅).
• As a comet designation prefix, indicates an object that was at first mistakenly identified as a comet, but is actually a minor planet (for example, A/2005 JM₃).
• The semi-major axis of an orbit.
• The symbol for the nitrogenous nucleic acid adenine, alanine and adenosine in biochemistry.
• A battery, a standard size of battery.
• The anode, a component of a vacuum tube.
• Haplogroup A (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup.
• Haplogroup A (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup.
• A human blood type, also A+ and A-.
• Vitamin A (also called retinol), an essential human nutrient.
• The center of a hexagonal face of the Brillouin zone of a hexagonal lattice, in physics.

Abbreviations for physical and chemical quantities and units:

• acceleration (a, upper-case for an initial/constant accleration value; lower case for an instantaneous acceleration variable)
• absorption coefficient (a)
• activity (a)
• hyperfine coupling constant (a)
• specific surface area (a)
• thermal diffusivity (a)
• the unique, or one of the, unit cell length(a)
• one of the van der Waals coefficients (a)
• Bohr radius (a₀)
• adsorbed
• are, the deprecated symbol for the unit of surface area equal to 100 square metres
• atto, the SI prefix meaning 10⁻¹⁸
• year, from the Latin annum, especially in geology, archeology and astronomy; as prefixed with Mega (Ma) or Giga (Ga) to indicate periods of time.
• magnetic vector potential (A)
• absorbance (A)
• absorption intensity (A)
• affinity of reaction (A)
• area (A)
• Einstein transition probability (A)
• Helmholtz energy, A
• hyperfine coupling constant (A)
• mass number (A)
• nucleon number (A)
• pre-exponential factor (A)
• radioactive activity (A)
• rotational constant (A)
• spin-orbit coupling constant (A)
• van der Waals-Hamaker constant (A)
• Hall coefficient (A_H)
• relative atomic mass (A_r)
• ampere (A) , the SI base unit of electric current

In mathematics:

• The area of geometric figures.
• A digit meaning ten in hexadecimal and other positional numeral systems with a radix of 11 or greater.
• Sometimes in blackboard bold represents the algebraic numbers (<math>\mathbb{A}</math> (U+1D538 in Unicode).

In logic:

• A symbol for the universal affirmative proposition in the general form "all x is y."
• The universal quantifier in symbolic logic (symbol ∀ or <math>\forall</math> (an inverted letter A).

In computing:

• As a programming language, A may refer to:
  • A-0 programming language
  • A+ programming language
  • A Sharp (Axiom), properly known as "A#", an object-oriented functional programming language
  • ARITH-MATIC, an extension of the A-2 programming language
  • BASIC A+, a programming language
• <a> is the HTML element for an anchor tag.
• In the Mac OS, Command-A (for All), and in Windows, Ctrl-A, and selects all the text in the document, or all the pixels of an image.
• A sometimes represents the set of all alphabetic characters within string patterns.
• A: is the conventional address of the first floppy disk drive in CP/M-based operating systems such as DOS.
• A is a security division ("Verified Protection") in the TCSEC.

The arts

• In fiction, the letter worn by Hester Prynne marking her as an adulteress in the Nathaniel Hawthorne novel The Scarlet Letter was an A.
• In film:
  • A is an Italian film made in 1969.
  • "A" is a Kannada movie directed by Upendra.
  • A (Rating), in the CBFC system.
  • In India, A is a movie rating, given to those intended to be seen only by adults.
• In music:
  • A (album), an album by progressive rock band Jethro Tull
  • A (Cass McCombs album), an album by Cass McCombs
  • A (band), a British alternative rock band.
  • A Band, an experimental group.
  • "A" (song), Ayumi Hamasaki's 10th single
  • "A", a song by the band Cartel
  • A (musical note), the sixth musical note.
  • A (song), a song by the band Barenaked Ladies.
  • A, or "side A," refers to the top or first side of a vinyl record.
• In poetry, A is the major work of influential twentieth century author Louis Zukofsky.

Languages

• A, an, the indefinite article in English.
• In French,
  • a is the Third person singular conjugation, Present tense of the verb avoir: «il a»="he has".
  • à is a conjunction meaning either "with", "at", or "to": «à la carte», «à moi»; although «au» is used in place of «à le» (for masculine singular nouns) and «aux» is used in place of «à les» (for plural nouns).
• In Spanish, a means to or towards.
• In Portuguese, it is either the feminine definite article or a preposition meaning "to", "toward".
• In Greek, a- is a prefix (alpha privativum) meaning "not" or "devoid of," used in many borrowed words in English, German and Romance languages (for example, amoral, asexual, arhythmic).
• A (kana), the Japanese kana あ and ア which may be used to represent Asia.
• In Esperanto as well as in Ido, -a is the adjectival/attributive ending; A is commonly an abbreviation meaning English (language).
• In Interlingua, a means at or to.

Other

• In American Major League Baseball,
  • The Oakland Athletics are often simply referred to as the "A's."
  • A can stand for Appearances or Assist.
• In calendars, A is often an abbreviation for the months April and August.
• In education, a grade of A typically represents the highest score that students can achieve. This is sometimes coupled with a plus/minus sign, as in A+ or A-, or a number, as in A1. It is occasionally a grade one level below A* (pronounced "A Star"). In Colombia, Finland, and New Zealand, A is the grade above a fail in a Pass ("Approve")/Fail test.
• In finance, A is the U.S. ticker symbol for Agilent Technologies.
• In games, the letter A is used to mark each of the Aces in a deck of playing cards.
• In international licence plate codes, A stands for Austria.
• In international paper sizes, A is a series of sizes with an aspect ratio of roughly 70% width to height, with A4 being an example popular size.
• In photography, most SLR cameras use A to signify aperture priority mode, where the user sets the aperture and the camera determines the shutter speed.

A in the Anarchist Symbol

• In political theory, an A in a full circle is an anarchist symbol.
• As the first letter of a postal code,
  • In Canada, A stands for Newfoundland and Labrador.
• In radio,
  • the NATO A band ranges below 0.25 GHz.
• On the serial numbers of United States dollars, A identifies the Federal Reserve Bank of Boston.
• In some sports, A is an abbreviation for Assists.
  • A is also a term used to signify the standard of grade a certain team is in comparison to another team of the same age. e.g. John is in the A team for soccer.
• In Christian theology, alpha is a metaphor for the beginning/creation of time and matter. It is sometimes translated to A.
• As a timezone, A is the military designation for Coordinated Universal Time+1, also known as CET or Central European Time.
• Topographically, A is used to describe an object shaped like the capital letter A, such as an A-frame.
• A (New York City Subway service), a service of the New York City Subway.
• A is a brassiere cup size.
• A name intended for a Swedish child born in 1991.

See also

• A#