The 18th letter in the Greek alphabet, the Sigma is our topic for today’s article. Here is everything you need to know about the Sigma symbol, its many meanings and uses in science and other fields

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**The Origins and History of the Greek Sigma Symbol**

Sigma (uppercase Σ, lowercase σ or in word-final position ς; Greek: σίγμα) is the 18th letter of the Greek alphabet. In the Greek numeral system, the Sigma symbol denotes the value of 200.

Sigma is the only one of the 24 Greek alphabet letters that has two different lowercase symbols. When in the middle of the word, the lowercase symbol σ is used, while the symbol ς is used when the small Sigma letter is at the end.

A great example would be the name Odysseus (Ὀδυσσεύς). Notice the difference between the two small Sigmas in the middle and the one at the end.

Furthermore, the capital Sigma’s epigraphic form has been simplified into a C-shaped symbol during the Hellenistic period. This variation, now known as the *lunate sigma*, became the standard form of capital Sigma until the Middle Ages.

The alphabetic position and appearance of the Sigma sign are thought to have been derived from the Phoenician letter shin, which resembles a W. Essentially, the Sigma takes the appearance of Shin, only rotated clockwise.

Some believed that Sigma’s original name may have been “san”. The historian Herodotus reported that the Dorians gave the name “san” to the letter known to Ionians as “sigma”.

It is also believed that the name “sigma” may have actually been invented by the Greeks to mean hissing.

The Greek alphabet letter Sigma has been adopted in the Old Italic alphabets. The simplified three-stroke sign, which omits the lowermost stroke, was widely adopted in Oscan, Etruscan, and Latin epigraphy.

The modified version of Sigma became the basis for the Latin S. Furthermore, the Coptic and Cyrillic letters C were derived from the lunate sigma.

**Uses and Meanings of the Greek Sigma Symbol**

Because of their distinct appearances, both the uppercase and lowercase Sigma symbols are widely used in different fields and industries, particularly in math and science.

The uppercase Sigma symbol is popular for being the symbol for the summation operator in math. Meanwhile, the lowercase Sigma sign is known for symbolizing the sigma receptor in biology.

Read on to learn more about the various usages for the Greek alphabet symbol Sigma.

**Uses for the Uppercase Sigma Symbol**

As mentioned above, the most popular use for the uppercase Sigma sign is for representing summation. Aside from that, it also denotes the busy beaver function in computer science.

In statistics and probability theory, the symbol denotes the covariance matrix of a set of random variables.

The symbol has various uses in physics as well. For one, it denotes a class of baryons, a type of composite subatomic particles, in particle physics.

Also in particle physics as well as nuclear physics, the capital Sigma represents macroscopic cross sections. Meanwhile, the symbol is also used to denote self-energy in the field of condensed matter physics.

In economics, the symbol represents the balance between invoice classes and overall amount of debts and demands.

In terms of both computer science and linguistics, the lowercase Sigma letter represents the set of symbols that form an alphabet.

**Uses for the Lowercase Sigma Symbol**

The lowercase Sigma sign represents more concepts and values than its uppercase counterpart.

As mentioned earlier, it symbolizes the sigma receptor in biology. It also represents the sigma factor of RNA polymerase.

The small Sigma letter also denotes the lifespan of a BMU or basic multicellular unit in bone remodeling. It was also used to represent a millisecond in 20th-century physiology texts.

The Greek alphabet letter Sigma’s lowercase symbol is also used in economics, business, and finance. Among its uses is to represent the volatility of a stock that is generally needed for options pricing.

On the other hand, it is used to denote the elasticity of substitution in macroeconomics.

In chemistry, the lowercase Sigma represents sigma bonds, as well as the sigma constant. In the field of physics, the symbol denotes various concepts including the cross section, the Stefan-Boltzmann constant, the measure of electrical conductivity, surface tension, velocity dispersion, surface charge density, normal stress, and the Pauli matrices.

In math and statistics, it symbolizes sigma-fields, sigma-algebras, and sigma-finiteness. You’d also see it representing the standard deviation of a population, the Weierstrass sigma-function, the sum-of-divisors function, and the generated sigma-algebra.

The symbol is also used in place of an “unknown angle”.

**How to Type the Sigma Symbol**

With so many uses for either the uppercase or lowercase Sigma symbol, you may find yourself needing to type or insert it into a document. Fortunately, there are several ways to type and insert the Sigma letter even though you’re not using a Greek keyboard.

**How to Type the Sigma Symbol in Word**

There are two basic ways to add a Sigma sign into a Word document. You can either use the ALT-code keyboard shortcut or use the Insert tab.

If you have a full keyboard with a numeric keypad, you can use the ALT-code shortcut. Press the ALT key and while holding onto it, type 228 to get the uppercase Sigma or 229 for the lowercase Sigma.

Meanwhile, to use the Insert tab, locate it on the Word functions menu. Click on Symbol > More Symbols to open the Symbol dialog box.

On the dialog box, make sure that the Subset field is set to Greek and Coptic. From the selection of symbols, look for the specific Sigma symbol you need. Then, click Insert and close the dialog box.

**How to Insert the Sigma Symbol in Excel**

You can also use the Insert function when you need to insert the Sigma sign into your Excel sheet. The steps are practically the same as you would insert the symbol into a Word document.

Furthermore, you can also check out lists of Greek alphabet letters online, then copy the uppercase or lowercase Sigma. Simply paste it on your Excel file, and voila, you’ve got the Sigma added.

**How to Type the Sigma Symbol on Mac**

If you’re using a Mac computer, you’re in luck. There’s a very easy way to type a Greek alphabet letter such as the Sigma on a Mac.

If you need the lowercase Sigma symbol, simply press and hold the CONTROL key, then press g + s. On the other hand, to type the uppercase Sigma, hit the caps lock button first before doing the CONTROL + G + S keyboard shortcut.