Omicron

Omicron (uppercase Ο, lowercase ο, literally "small o": Όμικρον, o mikron, 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 /o/. Letters that arose from omicron include Roman O and Cyrillic O.

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).

Omicron is used to designate the fifteenth star in a constellation group, its ordinal placement a function of both magnitude and position.^[1][2] Such stars include Omicron Andromedae, Omicron Ceti, and Omicron Persei.

Character encodings

• Greek Omicron / Coptic O^[3]

Character	Ο		ο		Ⲟ		ⲟ
Unicode name	GREEK CAPITAL LETTER OMICRON		GREEK SMALL LETTER OMICRON		COPTIC CAPITAL LETTER O		COPTIC SMALL LETTER O
Encodings	decimal	hex	decimal	hex	decimal	hex	decimal	hex
Unicode	927	U+039F	959	U+03BF	11422	U+2C9E	11423	U+2C9F
UTF-8	206 159	CE 9F	206 191	CE BF	226 178 158	E2 B2 9E	226 178 159	E2 B2 9F
Numeric character reference	Ο	Ο	ο	ο	Ⲟ	Ⲟ	ⲟ	ⲟ
Named character reference	Ο		ο
DOS Greek	142	8E	166	A6
DOS Greek-2	190	BE	233	E9
Windows 1253	207	CF	239	EF

• Mathematical Omicron^[4]

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.

Character	𝚶		𝛐		𝛰		𝜊		𝜪		𝝄
Unicode name	MATHEMATICAL BOLD CAPITAL OMICRON		MATHEMATICAL BOLD SMALL OMICRON		MATHEMATICAL ITALIC CAPITAL OMICRON		MATHEMATICAL ITALIC SMALL OMICRON		MATHEMATICAL BOLD ITALIC CAPITAL OMICRON		MATHEMATICAL BOLD ITALIC SMALL OMICRON
Encodings	decimal	hex	decimal	hex	decimal	hex	decimal	hex	decimal	hex	decimal	hex
Unicode	120502	U+1D6B6	120528	U+1D6D0	120560	U+1D6F0	120586	U+1D70A	120618	U+1D72A	120644	U+1D744
UTF-8	240 157 154 182	F0 9D 9A B6	240 157 155 144	F0 9D 9B 90	240 157 155 176	F0 9D 9B B0	240 157 156 138	F0 9D 9C 8A	240 157 156 170	F0 9D 9C AA	240 157 157 132	F0 9D 9D 84
UTF-16	55349 57014	D835 DEB6	55349 57040	D835 DED0	55349 57072	D835 DEF0	55349 57098	D835 DF0A	55349 57130	D835 DF2A	55349 57156	D835 DF44
Numeric character reference	𝚶	𝚶	𝛐	𝛐	𝛰	𝛰	𝜊	𝜊	𝜪	𝜪	𝝄	𝝄

Character	𝝤		𝝾		𝞞		𝞸
Unicode name	MATHEMATICAL SANS-SERIF BOLD CAPITAL OMICRON		MATHEMATICAL SANS-SERIF BOLD SMALL OMICRON		MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL OMICRON		MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL OMICRON
Encodings	decimal	hex	decimal	hex	decimal	hex	decimal	hex
Unicode	120676	U+1D764	120702	U+1D77E	120734	U+1D79E	120760	U+1D7B8
UTF-8	240 157 157 164	F0 9D 9D A4	240 157 157 190	F0 9D 9D BE	240 157 158 158	F0 9D 9E 9E	240 157 158 184	F0 9D 9E B8
UTF-16	55349 57188	D835 DF64	55349 57214	D835 DF7E	55349 57246	D835 DF9E	55349 57272	D835 DFB8
Numeric character reference	𝝤	𝝤	𝝾	𝝾	𝞞	𝞞	𝞸	𝞸

References

1. Martin, Martha Evans (1907). The Friendly Stars (1st ed.). New York: Harper & Brothers Publishers. p. 135. Retrieved 8 February 2016.
2. Wilk, Stephen R. (2007). Medusa: Solving the Mystery of the Gorgon (1st ed.). New York: Oxford University Press. p. 201. ISBN 9780199887736. Retrieved 8 February 2016.
3. "Greek and Coptic (Range: 0370–03FF)" (PDF). The Unicode Standard, Ver. 8.0. Unicode, Inc. 2015. Retrieved 8 February 2016.
4. "Mathematical Alphanumeric Symbols (Range: 1D400–1D7FF)" (PDF). The Unicode Standard, Ver. 8.0. Unicode, Inc. 2015. Retrieved 8 February 2016.