You’ve probably seen the regular asterisk on your keyboard hundreds of times, but there’s another asterisk that lives in the world of mathematics and formal notation.
The Asterisk Operator symbol (∗) looks similar to the everyday asterisk, yet it carries a very different purpose; it’s a dedicated mathematical operator used in algebra, convolution, and abstract math.
If you’ve ever spotted this symbol in a textbook, a research paper, or a LaTeX document and wondered how it differs from the one sitting above your 8 key, you’re about to get the full story.
Symbol Snapshot
Here’s everything you need to know about the Asterisk Operator symbol at a glance.
| Detail | Value |
|---|---|
| Symbol | ∗ |
| Name | Asterisk Operator |
| Unicode | U+2217 |
| HTML Entity | ∗ or ∗ |
| Alt Code (Windows) | Alt + 8727 (numeric keypad, with Unicode input enabled) |
| Category | Mathematical Symbols |
| On Keyboard | Not on standard keyboards; use character map, symbol insert, or copy-paste |
What Is the Asterisk Operator Symbol
The Asterisk Operator Symbol (∗) is a mathematical symbol that represents a general binary operation between two elements. You’ll find it most often in abstract algebra, signal processing, and formal mathematical typesetting where it denotes operations like multiplication, convolution, or group operations.
Unlike the standard keyboard asterisk (*), the Asterisk Operator symbol is specifically classified by Unicode as a math operator. This distinction matters because math typesetting systems, screen readers, and search engines treat the two characters differently.
Origin and History of the Asterisk Operator Symbol
The asterisk itself has ancient roots. The word comes from the Greek asteriskos, meaning “little star,” and scribes used star-shaped marks in manuscripts as far back as the second century BCE to flag corrections or annotations.
For centuries, the asterisk served as a general-purpose reference mark in printed text. When mathematicians needed a symbol for multiplication that wouldn’t be confused with the letter “x,” the asterisk became a natural candidate, especially in early computing where keyboard characters were limited.
As mathematical notation grew more precise in the 20th century, typographers and standards bodies recognized that a single asterisk character couldn’t serve every purpose.
The everyday asterisk (U+002A) was too tied to footnotes, wildcards, and programming. Mathematicians needed a version that was unambiguously an operator, one that typesetting systems could render at the correct size and vertical alignment for equations.
That’s how the Asterisk Operator symbol (U+2217) earned its own Unicode code point. It was included in the Unicode Standard’s Mathematical Operators block (U+2200 through U+22FF), giving it a permanent home alongside hundreds of other dedicated math symbols.
Understanding the Unicode Designation
Unicode is the universal system that assigns a unique number to every character used in digital communication, from letters and emoji to specialized math symbols. Think of it as a global address book for characters.
The Asterisk Operator symbol lives at U+2217, which places it in the Mathematical Operators block. This block runs from U+2200 to U+22FF and contains symbols like the plus-minus sign, the division sign, and many others used in formal math.
In HTML, you can display the Asterisk Operator using the named entity ∗ or the numeric entity ∗. Web developers use these codes to make sure the correct symbol renders in browsers, regardless of the reader’s operating system or font. For CSS, you can also use the escape \2217 inside a content property.
To use the Unicode code point directly, you’d type or paste the hex value 2217 into any application that supports Unicode input. On Windows in Microsoft Word, for example, you can type 2217 and then press Alt + X to convert it into the ∗ symbol instantly.
Meanings and Uses of the Asterisk Operator Symbol
Mathematics and Algebra
The Asterisk Operator symbol is a workhorse in formal math. In abstract algebra, it represents a general binary operation on a set, such as a group operation or ring multiplication.
When a textbook writes a ∗ b, it’s saying “apply the defined operation to a and b.” The beauty of this notation is its flexibility; the ∗ doesn’t commit to addition, multiplication, or any specific operation until the author defines it. This makes it perfect for proofs and definitions where the operation itself is the subject of study.
In more applied contexts, the symbol sometimes stands in for standard multiplication, especially in typeset documents where the author wants a cleaner look than the keyboard asterisk.
Signal Processing and Engineering
In signal processing, the Asterisk Operator symbol has a very specific meaning: convolution. When engineers write f ∗ g, they mean the convolution of two functions, a fundamental operation in filtering, image processing, and audio engineering.
Convolution combines two signals to produce a third, and it’s one of the most important operations in electrical engineering and data science. The ∗ symbol is the standard notation for this operation in textbooks, research papers, and technical documentation published by organizations like the IEEE.
Computer Science and Programming
Programmers encounter the Asterisk Operator symbol in several contexts. In languages that support operator overloading (like C++ or Python), the ∗ concept appears when defining custom multiplication or other binary operations for user-defined types.
In formal computer science writing, the Kleene star (which uses a superscript asterisk) denotes zero or more repetitions of a pattern in regular expressions and automata theory. The Asterisk Operator symbol sometimes appears in academic papers discussing these topics, especially when the author wants to distinguish the formal operator from the keyboard asterisk used in code.
LaTeX and Mathematical Typesetting
If you write math in LaTeX, you’ll use the command \ast to produce the Asterisk Operator symbol. LaTeX treats this as a binary operator, which means it automatically adds the correct spacing on either side of the symbol in an equation.
This is one of the key reasons the Asterisk Operator symbol exists as a separate character. In professional typesetting, spacing and alignment matter enormously, and the math-specific ∗ is designed to sit at the right vertical position and size within an equation.
Academic and Scientific Publishing
Research papers across physics, mathematics, and computer science rely on the Asterisk Operator symbol for formal notation. Journals and publishers expect authors to use U+2217 (or its LaTeX equivalent) rather than the keyboard asterisk when writing equations.
Using the correct symbol isn’t just about aesthetics. It ensures that digital papers are searchable, accessible, and rendered correctly across different PDF viewers and screen readers.
How to Type the Asterisk Operator Symbol
The Asterisk Operator symbol isn’t sitting on your keyboard, but there are reliable ways to type it on every major platform.
| Platform | Method | Steps |
|---|---|---|
| Windows | Character Map | Open Character Map, search for “asterisk operator,” select it, and click Copy |
| Windows | Word Alt + X | Type 2217 then press Alt + X |
| Windows | Symbol Picker (Win 11) | Press Win + . (period), search “asterisk,” and look for the math operator variant |
| Mac | Character Viewer | Press Control + Command + Space, search “asterisk operator,” and click to insert |
| Chromebook | Unicode Input | Enable Unicode input in settings, then press Ctrl + Shift + U, type 2217, and press Enter |
| iPhone/iPad | Copy-Paste | Copy ∗ from this page and paste where needed; or add a text replacement in Settings |
| Android | Copy-Paste | Copy ∗ from this page and paste; some keyboards like Gboard offer symbol search |
| Google Docs | Special Characters | Go to Insert → Special characters, search “asterisk operator,” and click to insert |
| Microsoft Word | Symbol Insert | Go to Insert → Symbol → More Symbols, set the font to “(normal text),” enter 2217 in the character code field, and click Insert |
Use It in a Sentence
Here are a few ways the Asterisk Operator shows up in practice.
- Abstract algebra: “Let (G, ∗) be a group where ∗ is the defined binary operation.”
- Signal processing: “The output signal is computed as h ∗ x, the convolution of the impulse response with the input.”
- Typesetting note: “Use
\astin LaTeX rather than*to get proper operator spacing in your equations.” - Academic writing: “The Asterisk Operator (∗) distinguishes the formal operation from a footnote marker.”
- Programming context: “In the documentation, ∗ represents the overloaded multiplication operator for the Matrix class.”
When Not to Use the Asterisk Operator Symbol
The Asterisk Operator is a math symbol, and using it outside of mathematical or technical contexts can cause confusion. Don’t use ∗ (U+2217) when you mean the regular keyboard asterisk (*) for footnotes, bullet points, or wildcard searches.
In programming source code, always use the standard asterisk (U+002A) because compilers and interpreters won’t recognize U+2217 as a valid operator. Using the wrong character in code will throw syntax errors that can be very hard to debug since the two symbols look nearly identical in many fonts.
In legal documents, financial reports, or regulated filings, stick with the standard asterisk or spell out the operation in words. The Asterisk Operator may not render correctly in all systems used by courts, regulators, or accounting software.
Pronunciation and Reading
Most people read the Asterisk Operator aloud as “star” or “asterisk” depending on the context. In abstract algebra, a ∗ b is often read as “a star b” or “a operated with b.”
In signal processing, f ∗ g is read as “f convolved with g” or “f star g.” The pronunciation depends on what the operation represents in the specific field.
Accessibility Note
Screen readers may announce the Asterisk Operator as “asterisk operator,” “low asterisk,” or simply “asterisk,” depending on the software. This inconsistency can confuse listeners who need to distinguish it from the regular keyboard asterisk.
If you’re writing for the web, consider adding an aria-label attribute or nearby plain-text context that clarifies the symbol’s meaning. For example, writing “the convolution operator (∗)” gives both sighted and non-sighted readers the information they need. The W3C’s guidelines on accessible math notation offer more detail on making mathematical symbols work for everyone.
Related Variants and Lookalike Symbols
Several symbols look like the Asterisk Operator but serve different purposes. Here’s how to tell them apart.
| Symbol | Name | Unicode | How It Differs |
|---|---|---|---|
| * | Asterisk | U+002A | The standard keyboard asterisk used for footnotes, wildcards, and multiplication in programming; not classified as a math operator |
| ⁎ | Low Asterisk | U+204E | A smaller asterisk positioned lower on the line, used in some typographic traditions as a reference mark |
| ✱ | Heavy Asterisk | U+2731 | A decorative, bolder asterisk used in graphic design and ornamental typography rather than math |
| ⊛ | Circled Asterisk Operator | U+229B | An asterisk enclosed in a circle, used in specialized mathematical notation to denote a distinct operation |
| × | Multiplication Sign | U+00D7 | The dedicated multiplication symbol; represents arithmetic multiplication specifically, not a general binary operation |
| · | Middle Dot | U+00B7 | A centered dot sometimes used for scalar multiplication or as a separator; visually and functionally distinct from any asterisk |
Fun Facts
The Asterisk Operator has some surprising stories behind it.
- The word “asterisk” comes from the Greek asteriskos, meaning “little star.” The symbol has been a star in manuscripts for over 2,000 years.
- In LaTeX, typing
\astgives you the Asterisk Operator with perfect math spacing, while typing a plain*gives you a completely different character with different spacing rules. - The Asterisk Operator and the regular asterisk are so visually similar that mixing them up in a document is one of the most common Unicode mistakes in academic publishing.
- Convolution, the operation most associated with ∗ in engineering, is the mathematical backbone of how Instagram filters, Photoshop blurs, and audio reverb effects work.
Frequently Asked Questions
What does the Asterisk Operator symbol mean?
The Asterisk Operator (∗) represents a general binary operation in mathematics, most commonly used in abstract algebra and convolution in signal processing. It’s distinct from the regular keyboard asterisk.
How do I type the Asterisk Operator on Windows?
In Microsoft Word, type 2217 and press Alt + X to convert it into the ∗ symbol. You can also open Character Map, search for “asterisk operator,” and copy it from there.
How do I type the Asterisk Operator on Mac?
Press Control + Command + Space to open the Character Viewer, then search for “asterisk operator” and click the symbol to insert it into your document.
What is the Unicode for the Asterisk Operator?
The Unicode code point for the Asterisk Operator is U+2217. It belongs to the Mathematical Operators block (U+2200 through U+22FF).
What is the HTML entity for the Asterisk Operator?
You can use the named entity ∗ or the numeric entity ∗ to display the Asterisk Operator in HTML.
What is the difference between ∗ and *?
The Asterisk Operator (∗, U+2217) is a dedicated mathematical operator with proper equation spacing. The regular asterisk (*, U+002A) is the keyboard character used for footnotes, wildcards, and multiplication in programming.
Can I use the Asterisk Operator in programming?
You should not use U+2217 in source code because compilers and interpreters expect the standard asterisk (U+002A). The Asterisk Operator is meant for mathematical typesetting and documentation, not executable code.
Now You Know the Asterisk Operator Symbol
The Asterisk Operator (∗) might look like an ordinary asterisk at first glance, but it carries its own Unicode identity, its own mathematical purpose, and its own rules for when and where to use it.
Next time you see it in a textbook or a research paper, you’ll know exactly what it means and why it’s not the same as the key above your 8.
If you know someone who writes math, code documentation, or academic papers, pass this article their way; they’ll thank you for it.