This article refers to the asterisk symbol. For other uses see Asterisk (disambiguation)
apostrophe ( ' ); ( ’ )
ampersand ( & )
An asterisk (*) is a typographical symbol or glyph. It is so called because it resembles a conventional image of a star (Latin astrum). Computer scientists often pronounce it as star (as, for example, in the A* algorithm).
The asterisk derives from the need of the printers of family trees in feudal times for a symbol to indicate date of birth. The original shape was six-armed, each arm like a teardrop shooting from the center. For this reason, in some computer circles it is called a splat, perhaps due to the "squashed-bug" appearance of the asterisk on many early line printers.
In this form the character appeared in typewriters. However, some typewriters had difficulty printing the six arms distinctly. Furthermore, due to Arab-Israeli tension, many Arabs would not buy typewriters with a six-armed symbol, which they identified with the Star of David on the Israeli flag. Hence many systems use a five-armed symbol, referred to as the "Arabic star", and given a distinct character in Unicode, U+066D (٭).
Uses of the asterisk include:
- In written text, the asterisk is used to call out a footnote or otherwise mark something.
- In informal plain text computer documents (e.g., in e-mail messages or newsgroup postings), asterisks are used for emphasis (usually by bracketing the text with asterisks *like this*). Usually, this is done when other means of emphasis, like boldfacing, italicizing, or underlining are not available in the system.
- In linguistics:
- In computer science, the asterisk is used in regular expressions to denote zero or more repetitions of a pattern; this use is known as the Kleene star or Kleene closure after Stephen Kleene.
- In the Unified Modelling Language, the asterisk is used to denote zero to many classes.
- In some computer interfaces, such as the Unix shell and Microsoft's Command Prompt, the asterisk is the wildcard character and stands for any string of characters. This is also known as a wildcard symbol.
- Many programming languages and calculators use the asterisk as a symbol for multiplication. It also has a number of special meanings in specific languages, for instance:
- In the C programming language, the asterisk is used to get the contents of a pointer. It is the inverse of the & operator which gives the address of a variable. It is also used declare a pointer variable.
- In the Perl programming language, the asterisk is used to refer to the typeglob of all variables with a given name.
- In the Common Lisp programming language, the names of global variables are conventionally set off with asterisks, *like-this*.
- In mathematics, it signifies the complex conjugate of a complex number, e.g. if x=a+ib, x*=a-ib. It is also used as an infix binary operator. The lowered asterisk is a symbol for convolution, e.g. f ∗ g is a convolution of f with g.
- On a Touch-Tone telephone keypad, * (called star) is one of the two special keys, and is found on the left of the zero. (The other is the number sign ("pound" or "hash")).
- In many instant message communication programs (such as AOL Instant Messenger and Yahoo! Messenger), chat rooms, and message boards, it is placed at the beginning of a line correcting a typographical error.
- Some e-mail, Usenet, and instant messenger users place asterisks around a word or phrase for emphasis (as opposed to using all caps, which signifies shouting and is considered rude).
- In cricket, it signifies a total number of runs scored by a batsman without losing his wicket, e.g. 107* means '107 not out'.
- In the GCSE examination, A* ("A-star") is a special top grade that is distinguished from grade A.
- In many MUDs and MOOs, as well as 'male', 'female' and other more esoteric genders, there is a gender called 'splat', which uses an asterisk to replace the letters that differ in standard English gender pronouns. For example, h* is used rather than him or her.
In fine mathematical typography the Unicode character U+2217 (∗) "math asterisk" is available (HTML entity ∗). This character, also appeared in the position of the regular asterisk in the PostScript symbol character set in the Symbol font included with Windows and Macintosh operating systems and with many printers. It should be used in fine typography for a large asterisk that lines up with the other mathematical operators.
A group of three asterisks arranged in a triangular formation is called an asterism.
The asterisk and computing
Unicode also encodes "two asterisks aligned vertically" as the character U+2051. The asterism is encoded as U+2042. There are also many other asterisk-like characters.
* ⁎ ⁑ ∗ ⊛ ✢ ✣ ✤ ✥ ✱ ✲ ✳ ✺ ✻ ✼ ✽ ❃ ❉ ❊ ❋ ⧆ ⩮ ﹡ ＊