Omicron

Greek alphabet
Αα Alpha Νν Nu Ββ Beta Ξξ Xi Γγ Gamma Οο Omicron Δδ Delta Ππ Pi Εε Epsilon Ρρ Rho Ζζ Zeta Σσς Sigma Ηη Eta Ττ Tau Θθ Theta Υυ Upsilon Ιι Iota Φφ Phi Κκ Kappa Χχ Chi Λλ Lambda Ψψ Psi Μμ Mu Ωω Omega
History
Archaic local variants Diacritics Ligatures Numerals ϛ (6) ϟ (90) ϡ (900)
Use in other languages
Bactrian Coptic Albanian
Related topics
Use as scientific symbols
Category
v t

Omicron /ˈɒmɪkrɒn, oʊˈmaɪkrɒn/^[1] (uppercase Ο, lowercase ο, literally 'small o': όμικρον < ὂ μικρόν - ò mikrón, micron meaning 'small' in contrast to omega) is the 15th letter of the Greek alphabet. In the system of Greek numerals it has a value of 70. This letter is derived from the Phoenician letter ayin . In classical Greek, omicron represented the sound [o] in contrast to omega [ɔː] and ου [oː]. In modern Greek, omicron represents the mid back rounded vowel /o̞/ , the same sound as omega. Letters that arose from omicron include Roman O and Cyrillic O.

Use[]

In addition to its use as an alphabetic letter, omicron is occasionally used in technical notation, but its use is limited since both upper case and lower case (Ο ο) are indistinguishable from the Latin letter "oh" (O o) and difficult to distinguish from the Hindu-Arabic numeral "zero" (0).

Mathematics[]

The upper-case letter of omicron (O) was originally used in mathematics as a symbol for Big O notation (representing a function's asymptotic growth rate), but has fallen out of favor because omicron is indistinguishable from the Latin letter O and easily confused with the digit zero (0). Where "Big O" notation is still used, Omicron is generally replaced with a script- or calligraphic-form Latin letter "Oh" (${\displaystyle {\mathcal {O}}}$).

Greek numerals[]

There were several systems for writing numbers in Greek; the most common form used in late classical era used omicron (either upper or lower case) to represent the value 70.

More generally, the letter omicron is used to mark the fifteenth ordinal position in any Greek-alphabet marked list. So for example, in Euclid's Elements, when various points in a geometric diagram are marked with letters, it is effectively the same as marking them with numbers, each letter representing the number of its place in the standard alphabet.^[a][b]

Astronomy[]

Omicron is used to designate the fifteenth star in a constellation group, its ordinal placement an irregular function of both magnitude and position.^[2][3] Such stars include Omicron Andromedae, Omicron Ceti, and Omicron Persei.

In Claudius Ptolemy's (c. 100–170 ) Almagest, tables of sexagesimal numbers 1 ... 59 are represented in the conventional manner^[c] for Greek numbers: ′α ... ′νθ . Since the letter omicron [which represents 70 (′ο) in the standard system] is not used in sexagesimal, it is re-purposed to represent an empty number cell. In some renditions the cell was just left blank (nothing there = value is zero), but to avoid copying errors, positively marking a zero cell with omicron was preferred, in the same way that blank cells in modern tables are filled with a dash (—). Both an omicron and a dash imply that "this isn't a mistake, the cell is actually supposed to be empty". By coincidence, the ancient zero-value omicron (ο) resembles a modern Hindu-Arabic zero (0).

Character encodings[]

• Greek Omicron / Coptic O^[4]

• Mathematical Omicron^[5]

These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.