A compass rose or compass star, sometimes called a wind rose or rose of the winds, is a polar diagram displaying the orientation of the cardinal directions (north, east, south, and west) and their intermediate points. It is used on compasses (including magnetic ones), maps (such as compass rose networks), or monuments. It is particularly common in navigation systems, including nautical charts, non-directional beacons (NDB), VHF omnidirectional range (VOR) systems, satellite navigation devices ("GPS").
Types
Linguistic anthropological studies have shown that most human communities have four points of cardinal direction. The names given to these directions are usually derived from either locally-specific geographic features (e.g. "towards the hills", "towards the sea") or from celestial bodies (especially the sun) or from atmospheric features (winds, temperature).Brown, C.H. (1983) "Where do Cardinal Direction Terms Come From?", Anthropological Linguistics, Vol. 25 (2), pp. 121–61. Most mobile populations tend to adopt sunrise and sunset for East and West and the direction from where different winds blow to denote North and South.
Classical
The ancient Greeks originally maintained distinct and separate systems of points and winds. The four Greek cardinal points (, , and ) were based on celestial bodies and used for orientation. The four Greek winds (, , , ) were confined to meteorology. Nonetheless, both systems were gradually conflated, and wind names came eventually to denote cardinal directions as well.D'Avezac, M.A.P. (1874) Aperçus historiques sur la rose des vents: lettre à Monsieur Henri Narducci. Rome: Civelli
In his meteorological studies, Aristotle identified ten distinct winds: two north–south winds (, ) and four sets of east–west winds blowing from different latitudes—the Arctic Circle (, ), the summer solstice horizon (, ), the equinox (, ) and the winter solstice (, ). Aristotle's system was asymmetric. To restore balance, Timosthenes of Rhodes added two more winds to produce the classical 12-wind rose, and began using the winds to denote geographical direction in navigation. Eratosthenes deducted two winds from Aristotle's system, to produce the classical eight-wind rose.
The Romans (e.g. Seneca, Pliny) adopted the Greek 12-wind system, and replaced its names with Latin equivalents, e.g. , , , , etc. The De architectura of the Roman architect Vitruvius describes 24 winds.
According to the chronicler Einhard (), the Frankish king Charlemagne himself came up with his own names for the classical 12 winds.Einhard, Vita Karoli Imp., [Lat: (Eng.(p. 22)(p. 68) During the Migration Period, the Germanic names for the cardinal directions entered the Romance languages, where they replaced the Latin names borealis with north, australis with south, occidentalis with west and orientalis with east.See e.g. Weibull, Lauritz. De gamle nordbornas väderstrecksbegrepp. Scandia 1/1928; Ekblom, R. Alfred the Great as Geographer. Studia Neophilologica 14/1941-2; Ekblom, R. Den forntida nordiska orientering och Wulfstans resa till Truso. Förnvännen. 33/1938; Sköld, Tryggve. Isländska väderstreck. Scripta Islandica. Isländska sällskapets årsbok 16/1965.
The following table gives a rough equivalence of the classical 12-wind rose with the modern compass directions (The directions are imprecise since it is not clear at what angles the classical winds are supposed to be with each other; some have argued that they should be equally spaced at 30 degrees each; for more details, see the article on Classical compass winds).
Wind Greek Roman Frankish N () or () NNE () NE () E () SE () SSE () S () SSW () or SW () W () NW () NNW () or
Sidereal
The sidereal compass rose demarcates the compass points by the position of stars ("steering stars"; not to be confused with zenith stars) in the night sky, rather than winds. Arab navigators in the Red Sea and the Indian Ocean, who depended on celestial navigation, were using a 32-point sidereal compass rose before the end of the 10th century.Saussure, L. de (1923) "L'origine de la rose des vents et l'invention de la boussole", Archives des sciences physiques et naturelles, vol. 5, no.2 & 3, pp. 149–81 and 259–91.Taylor, E.G.R. (1956) The Haven-Finding Art: A history of navigation from Odysseus to Captain Cook, 1971 ed., London: Hollis and Carter., pp. 128–31.Tolmacheva, M. (1980) "On the Arab System of Nautical Orientation", Arabica, vol. 27 (2), pp. 180–92. In the Northern Hemisphere, the steady Pole Star (Polaris) was used for the N–S axis; the less-steady Southern Cross had to do for the Southern Hemisphere, as the southern pole star, Sigma Octantis, is too dim to be easily seen from Earth with the naked eye. The other thirty points on the sidereal rose were determined by the rising and setting positions of fifteen bright stars. Reading from North to South, in their rising and setting positions, these are:List comes from Tolmacheva (1980:p. 183), based "with some reservations" on Tibbets (1971: p. 296, n. 133). The sidereal rose given in Lagan (2005: p. 66) has some differences, e.g. placing Orion's belt in East and Altair in EbN.
Point Star N Polaris NbE "the Guards" (Ursa Minor) NNE Alpha Ursa Major NEbN Alpha Cassiopeiae NE Capella NEbE Vega ENE Arcturus EbN the Pleiades E Altair EbS Orion's belt ESE Sirius SEbE Beta Scorpionis SE Antares SEbS Alpha Centauri SSE Canopus SbE Achernar S Southern Cross
The western half of the rose would be the same stars in their setting position. The true position of these stars is only approximate to their theoretical equidistant rhumbs on the sidereal compass. Stars with the same declination formed a "linear constellation" or to provide direction as the night progressed.M.D. Halpern (1985) The Origins of the Carolinian Sidereal Compass, Master's thesis, Texas A & M University
A similar sidereal compass was used by Polynesian and Micronesian navigators in the Pacific Ocean, although different stars were used in a number of cases, clustering around the east–west axis.
Mariner's
In Europe, the Classical 12-wind system continued to be taught in academic settings during the Medieval era, but seafarers in the Mediterranean came up with their own distinct 8-wind system. The mariners used names derived from the Mediterranean lingua franca, composed principally of Ligurian, mixed with Venetian, Sicilian, Provençal, Catalan, Greek and Arabic terms from around the Mediterranean basin. (N) Tramontana (NE) Greco (or Bora) (E) Levante (SE) Scirocco (or Exaloc) (S) Ostro (or Mezzogiorno) (SW) Libeccio (or Garbino) (W) Ponente (NW) Maestro (or Mistral)
The exact origin of the mariner's eight-wind rose is obscure. Only two of its point names (Ostro, Libeccio) have Classical etymologies, the rest of the names seem to be autonomously derived. Two Arabic words stand out: Scirocco (SE) from al-Sharq (الشرق – east in Arabic) and the variant Garbino (SW), from al-Gharb (الغرب – west in Arabic). This suggests the mariner's rose was probably acquired by southern Italian seafarers; not from their classical Roman ancestors, but rather from Norman Sicily in the 11th to 12th centuries.Taylor, E.G. R. (1937) "The 'De Ventis' of Matthew Paris", Imago Mundi, vol. 2, p. 25. The coasts of the Maghreb and Mashriq are SW and SE of Sicily respectively; the Greco (a NE wind), reflects the position of Byzantine-held Calabria-Apulia to the northeast of Arab Sicily, while the Maestro (a NW wind) is a reference to the Mistral wind that blows from the southern French coast towards northwest Sicily.
The 32-point compass used for navigation in the Mediterranean by the 14th century, had increments of 11° between points. Only the eight principal winds (N, NE, E, SE, S, SW, W, NW) were given special names. The eight half-winds just combined the names of the two principal winds, e.g. Greco-Tramontana for NNE, Greco-Levante for ENE, and so on. Quarter-winds were more cumbersomely phrased, with the closest principal wind named first and the next-closest principal wind second, e.g. "Quarto di Tramontana verso Greco" (literally, "one quarter wind from North towards Northeast", i.e. North by East), and "Quarto di Greco verso Tramontana" ("one quarter wind from NE towards N", i.e. Northeast by North). Boxing the compass (naming all 32 winds) was expected of all Medieval mariners.
Depiction on nautical charts
In the earliest medieval portolan charts of the 14th century, compass roses were depicted as mere collections of color-coded compass rhumb lines: black for the eight main winds, green for the eight half-winds and red for the sixteen quarter-winds.Wallis, H.M. and J.H. Robinson, editors (1987) Cartographical Innovations: An international handbook of mapping terms to 1900. London: Map Collector Publications. The average portolan chart had sixteen such roses (or confluence of lines), spaced out equally around the circumference of a large implicit circle.
The cartographer Cresques Abraham of Mallorca, in his Catalan Atlas of 1375, was the first to draw an ornate compass rose on a map. By the end of the 15th century, Portuguese cartographers began drawing multiple ornate compass roses throughout the chart, one upon each of the sixteen circumference roses (unless the illustration conflicted with coastal details).
The points on a compass rose were frequently labeled by the initial letters of the mariner's principal winds (T, G, L, S, O, L, P, M). From the outset, the custom also began to distinguish the north from the other points by a specific visual marker. Medieval Italian cartographers typically used a simple arrowhead or circumflex-hatted T (an allusion to the compass needle) to designate the north, while the Majorcan cartographic school typically used a stylized Pole Star for its north mark.Winter, Heinrich (1947) "On the Real and the Pseudo-Pilestrina Maps and Other Early Portuguese Maps in Munich", Imago Mundi, vol. 4, pp. 25–27. The use of the fleur-de-lis as north mark was introduced by Pedro Reinel, and quickly became customary in compass roses (and is still often used today). Old compass roses also often used a Christian cross at Levante (E), indicating the direction of Jerusalem from the point of view of the Mediterranean sea.Dan Reboussin (2005). Wind Rose. University of Florida. Retrieved on 2009-04-26.
The twelve Classical winds (or a subset of them) were also sometimes depicted on portolan charts, albeit not on a compass rose, but rather separately on small disks or coins on the edges of the map.
The compass rose was also depicted on traverse boards used on board ships to record headings sailed at set time intervals.
Modern depictions
The contemporary compass rose appears as two rings, one smaller and set inside the other. The outside ring denotes true cardinal directions while the smaller inside ring denotes magnetic cardinal directions. True north refers to the geographical location of the North Pole while magnetic north refers to the direction towards which the north pole of a magnetic object (as found in a compass) will point. The angular difference between true and magnetic north is called variation, which varies depending on location. The angular difference between magnetic heading and compass heading is called deviation which varies by vessel and its heading. North arrows are often included in contemporary maps as part of the map layout. The modern compass rose has eight principal winds. Listed clockwise, these are:
Compass point Abbr. Heading Traditional wind North N 0° Tramontana North-east NE 45° (45°×1) Greco or Grecale East E 90° (45°×2) Levante South-east SE 135° (45°×3) Scirocco South S 180° (45°×4) Ostro or Mezzogiorno South-west SW 225° (45°×5) Libeccio or Garbino West W 270° (45°×6) Ponente North-west NW 315° (45°×7) Maestro, Maestrale or Mistral