Rho

Rho /ˈr/ (uppercase Ρ, lowercase ρ or ϱ; Greek: ρο or ρω) is the seventeenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 100. It is derived from Phoenician letter res . Its uppercase form uses the same glyph, Ρ, as the distinct Latin letter P; the two letters have different Unicode encodings.

Uses

The Greek alphabet on a black figure vessel, with an R-shaped rho.

Greek

Rho is classed as a liquid consonant (together with Lambda and sometimes the nasals Mu and Nu), which has important implications for morphology. In both Ancient and Modern Greek, it represents a alveolar trill IPA: [r], alveolar tap IPA: [ɾ], or alveolar approximant IPA: [ɹ].

In polytonic orthography, a rho at the beginning of a word is written with a rough breathing, equivalent to h ( rh), and a double rho within a word is written with a smooth breathing over the first rho and a rough breathing over the second (ῤῥ rrh). That apparently reflected an aspirated or voiceless pronunciation in Ancient Greek, which led to the various Greek-derived English words starting with rh or containing rrh.

The name of the letter is written in Greek as ῥῶ (polytonic) or ρω/ρο (monotonic).

Other alphabets

Letters that arose from rho include Roman R and Cyrillic Er (Р).

Mathematics and science

The characters ρ and ϱ are also conventionally used outside the Greek alphabetical context in science and mathematics.

Chi Rho

The letter rho overlaid with chi forms the Chi Rho symbol, used to represent Jesus Christ.

Rho with stroke (ϼ)

The rho with a stroke through its tail is used for abbreviations involving rho, most notably in γϼ for γράμμα as a unit of measurement.[1]

Character encodings

Greek rho[2]

Character information
PreviewΡρ
Unicode name GREEK CAPITAL LETTER RHO GREEK SMALL LETTER RHO GREEK CAPITAL LETTER RHO WITH DASIA GREEK SMALL LETTER RHO WITH DASIA GREEK SMALL LETTER RHO WITH PSILI
Encodingsdecimalhexdechexdechexdechexdechex
Unicode929U+03A1961U+03C18172U+1FEC8165U+1FE58164U+1FE4
UTF-8206 161CE A1207 129CF 81225 191 172E1 BF AC225 191 165E1 BF A5225 191 164E1 BF A4
Numeric character referenceΡΡρρῬῬῥῥῤῤ
Named character referenceΡρ
DOS Greek14490168A8
DOS Greek-2199C7235EB
Windows 1253209D1241F1
TeX\rho

Greek rho symbols

Character information
Previewϱϼ
Unicode name GREEK RHO SYMBOL GREEK RHO WITH STROKE SYMBOL GREEK LETTER SMALL CAPITAL RHO GREEK SUBSCRIPT SMALL LETTER RHO CHI RHO
Encodingsdecimalhexdechexdechexdechexdechex
Unicode1009U+03F11020U+03FC7465U+1D297528U+1D689767U+2627
UTF-8207 177CF B1207 188CF BC225 180 169E1 B4 A9225 181 168E1 B5 A8226 152 167E2 98 A7
Numeric character referenceϱϱϼϼᴩᴩᵨᵨ☧☧
Named character referenceϱ, ϱ
TeX\varrho

Coptic ro

Character information
Preview
Unicode name COPTIC CAPITAL LETTER RO COPTIC SMALL LETTER RO COPTIC SYMBOL CHI RHO
Encodingsdecimalhexdechexdechex
Unicode11426U+2CA211427U+2CA311497U+2CE9
UTF-8226 178 162E2 B2 A2226 178 163E2 B2 A3226 179 169E2 B3 A9
Numeric character referenceⲢⲢⲣⲣ⳩⳩

Functional symbol

Character information
Preview
Unicode name APL FUNCTIONAL SYMBOL RHO
Encodingsdecimalhex
Unicode9076U+2374
UTF-8226 141 180E2 8D B4
Numeric character reference⍴⍴

Mathematical rho

Character information
Preview𝚸𝛒𝛠𝛲𝜌
Unicode name MATHEMATICAL BOLD
CAPITAL RHO
MATHEMATICAL BOLD
SMALL RHO
MATHEMATICAL BOLD
RHO SYMBOL
MATHEMATICAL ITALIC
CAPITAL RHO
MATHEMATICAL ITALIC
SMALL RHO
Encodingsdecimalhexdechexdechexdechexdechex
Unicode120504U+1D6B8120530U+1D6D2120544U+1D6E0120562U+1D6F2120588U+1D70C
UTF-8240 157 154 184F0 9D 9A B8240 157 155 146F0 9D 9B 92240 157 155 160F0 9D 9B A0240 157 155 178F0 9D 9B B2240 157 156 140F0 9D 9C 8C
UTF-1655349 57016D835 DEB855349 57042D835 DED255349 57056D835 DEE055349 57074D835 DEF255349 57100D835 DF0C
Numeric character reference𝚸𝚸𝛒𝛒𝛠𝛠𝛲𝛲𝜌𝜌
Character information
Preview𝜚𝜬𝝆𝝔𝝦
Unicode name MATHEMATICAL ITALIC
RHO SYMBOL
MATHEMATICAL BOLD ITALIC
CAPITAL RHO
MATHEMATICAL BOLD ITALIC
SMALL RHO
MATHEMATICAL BOLD ITALIC
RHO SYMBOL
MATHEMATICAL SANS-SERIF
BOLD CAPITAL RHO
Encodingsdecimalhexdechexdechexdechexdechex
Unicode120602U+1D71A120620U+1D72C120646U+1D746120660U+1D754120678U+1D766
UTF-8240 157 156 154F0 9D 9C 9A240 157 156 172F0 9D 9C AC240 157 157 134F0 9D 9D 86240 157 157 148F0 9D 9D 94240 157 157 166F0 9D 9D A6
UTF-1655349 57114D835 DF1A55349 57132D835 DF2C55349 57158D835 DF4655349 57172D835 DF5455349 57190D835 DF66
Numeric character reference𝜚𝜚𝜬𝜬𝝆𝝆𝝔𝝔𝝦𝝦
Character information
Preview𝞀𝞎𝞠𝞺𝟈
Unicode name MATHEMATICAL SANS-SERIF
BOLD SMALL RHO
MATHEMATICAL SANS-SERIF
BOLD RHO SYMBOL
MATHEMATICAL SANS-SERIF
BOLD ITALIC CAPITAL RHO
MATHEMATICAL SANS-SERIF
BOLD ITALIC SMALL RHO
MATHEMATICAL SANS-SERIF
BOLD ITALIC RHO SYMBOL
Encodingsdecimalhexdechexdechexdechexdechex
Unicode120704U+1D780120718U+1D78E120736U+1D7A0120762U+1D7BA120776U+1D7C8
UTF-8240 157 158 128F0 9D 9E 80240 157 158 142F0 9D 9E 8E240 157 158 160F0 9D 9E A0240 157 158 186F0 9D 9E BA240 157 159 136F0 9D 9F 88
UTF-1655349 57216D835 DF8055349 57230D835 DF8E55349 57248D835 DFA055349 57274D835 DFBA55349 57288D835 DFC8
Numeric character reference𝞀𝞀𝞎𝞎𝞠𝞠𝞺𝞺𝟈𝟈

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.

See also

References

  1. Paul of Aegina explains conventional usage in the last chapter of Book VII on weights and measures and uses it throughout his work.
  2. Unicode Code Charts: Greek and Coptic (Range: 0370-03FF)
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