Asterisk

This article refers to the typographical symbol. For other uses, see Asterisk (disambiguation). For the similarly-named cartoon character, see Asterix.

An asterisk in eurostyle font

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 is sometimes mistakenly referred to as an asterix, in a case of reverse etymology.

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 distinct symbol referred to as the "Arabic star," and given a distinct character in Unicode, U+066D and the official name "Arabic five-pointed star."

In some fonts, however, the asterisk is five-pointed and the Arabic star is eight-pointed. The two symbols are compared below (the display depends on your browser's font).

Asterisk	Arabic star
*	٭

Uses

Written text

• In written text, the asterisk is used to call out a footnote or otherwise mark something of note.
• Also in written text, an asterisk may also be used to block out portions of a profanity to reduce offence. For example: f**k

Linguistics

Historical linguistics

• In historical linguistics, an asterisk next to a word indicates that the word is a historically reconstructed and unattested form.

Generativist tradition in linguistics

• In generativism, especially syntax, an asterisk next to a word or phrase indicates that the word or phrase is ungrammatical.

Computer science

• 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 Modeling Language, the asterisk is used to denote zero to many classes.

Computer interfaces

• 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. A common use of the wildcard is in searching for files on a computer. For instance, if a user wished to find a document called Document 1, search terms like Doc* and D*ment* would return the file.

• In some graphical interfaces, particularly Microsoft applications, an asterisk is prepended to the current working document name shown in a window's title bar to indicate that unsaved changes exist.

Programming languages

• 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 to declare a pointer variable.
  • In the Common Lisp programming language, the names of global variables are conventionally set off with asterisks, *LIKE-THIS*.
  • In the Fortran programming language, and in some dialects of the Pascal programming language, it is used to signify exponentiation, e.g. 5*3 = 15 while 5**3 is 5*5*5 or 125.
  • In the Perl programming language, the asterisk is used to refer to the typeglob of all variables with a given name.
  • In the programming languages Ruby and Python, * has two specific uses. Firstly, the unary * operator applied to a list object inside a function call will expand that list into the arguments of the function call. Secondly, a parameter preceded by * in the parameter list for a function will result in any extra parameters being aggregated into a list.

Mathematics

The asterisk has many uses in mathematics. Among them are

• The complex conjugate of a complex number (though more common notation is ${\bar {z}}$).
• The free product of two groups.
• Infix notation for an arbitrary binary operator.
• Convolution, e.g. f ∗ g is a convolution of f with g.
• The multiplicative group of a ring, especially when the ring is a field. E.g. $\mathbb {C} ^{*}=\mathbb {C} -\{0\}$
• An arbitrary point in some set, for example in computing Riemann sums or when contracting a simply connected group to the singleton set { ∗ }.
• The dual space of a vector space V is denoted V*.
• The push forward of a smooth map f between two smooth manifolds is denoted f_*.
• The Hodge dual operator on vector spaces $*:A^{k}\rightarrow A^{n-k}$.

The asterisk is also often used to in all branches of mathematics designate a correspondance between two mathematical entities represented by a single letter--one with the asterisk and one without.

Telephony

• On a Touch-Tone telephone keypad, * (called star, or less commonly, palm) 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")).

• Asterisk is also the name of a free software / open-source software implementation of a telephone private branch exchange (PBX).

E-mail, Usenet, IM

• 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. Asterisks are also used in this fashion to show an action (eg. *jump* or *glomp*), especially in text RPGs where unformatted text denotes speech.
• In chatrooms and instant messaging, an asterisk is often used to correct a typo. Usage varies on whether the asterisk comes before or after the correction. For example:
  

User1: What do yuo think

User1: *you

User2: Wht,

User2: What?**

Cricket

• In cricket, it signifies a total number of runs scored by a batsman without losing his wicket, e.g. 107* means '107 not out'. When written before a player's name on a scorecard, it indicates the captain.

• It is also used on television when giving a career statistic during a match. For example, 47* in a number of matches column means that the current game is the players 47th.

Economics

• In economics, the use of an asterisk after a letter indicating a variable such as price, output or employment indicates that the variable is at its optimal level (that which is achieved in a perfect market situation). For inastance, p* is the price level p when output y is at its corresponding optimal level of y*.

Education

• In the GCSE examination, A* ("A-star") is a special top grade that is distinguished from grade A.

Games

• 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. Also, asterisks are used to signify doing an action, for example, '*action*'

Mathematical typography

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.

Baseball

• In recent years, the asterisk has come into use on scorecards to denote a "great defensive play." [1]
• In colloquial usage, an asterisk is used to indicated that a record is somehow tainted by circumstances, which are putatively explained in a footnote supposedly referenced by the asterisk. This usage arose after the 1961 baseball season in which Roger Maris of the New York Yankees broke Babe Ruth's 34-year-old single-season home run record. Because Ruth had amassed 60 home runs in a season with only 154 games, compared to Maris' 61 over 162 games, baseball commissioner Ford Frick announced that Maris' accomplishment would be recorded in the record books with an explanation (often referred to as "an asterisk" in the retelling). In fact, Major League Baseball has no official record book, but the stigma remained with Maris for many years, and the concept of a real or figurative asterisk denoting less-than-official records has become widely used in sports and other competitive endeavors. A 2001 TV movie about Maris' record-breaking season was called 61* (pronounced sixty-one asterisk) in reference to the controversy.

Horse Racing

• In programmes distributed at race tracks, an asterisk next to a jockey's name indicates that he or she is an apprentice, and in many cases is allowed to ride at a slightly lesser weight than the other jockeys. Such a jockey is sometimes called a “bug boy” because of the asterisk's bug-like appearance.