Points of the compass

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The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directionsnorth, east, south, and west—each separated by 90 degrees, and secondarily divided by four ordinal (intercardinal) directions—northeast, southeast, southwest, and northwest—each located halfway between two cardinal directions. Some disciplines such as meteorology and navigation further divide the compass with additional azimuths. Within European tradition, a fully defined compass has 32 'points' (and any finer subdivisions are described in fractions of points). [1]

Contents

Compass points are valuable in that they allow a user to refer to a specific azimuth in a colloquial fashion, without having to compute or remember degrees. [2]

Designations

The names of the compass point directions follow these rules:

8-wind compass rose

8-wind compass rose Compass rose en 08p.svg
8-wind compass rose

16-wind compass rose

32-wind compass rose

32-point compass rose Brosen windrose Full.svg
32-point compass rose

In summary, the 32-wind compass rose comes from the eight principal winds, eight half-winds and sixteen quarter-winds combined, with each compass point at an 11+14° angle from the next.

In the mariner's exercise of boxing the compass, all thirty-two points of the compass are named in clockwise order. [6]

Half- and quarter-points

Compass rose from "American Practical Navigator" 1916 Bowditch1916p15CompassRose.png
Compass rose from "American Practical Navigator" 1916

By the middle of the 18th century, the 32-point system had been further extended by using half- and quarter-points to give a total of 128 directions. [7] These fractional points are named by appending, for example 1/4east, 1/2east, or 3/4east to the name of one of the 32 points. Each of the 96 fractional points can be named in two ways, depending on which of the two adjoining whole points is used, for example, N3/4E is equivalent to NbE1/4N. Either form is easily understood, but alternative conventions as to correct usage developed in different countries and organisations. "It is the custom in the United States Navy to box from north and south toward east and west, with the exception that divisions adjacent to a cardinal or inter-cardinal point are always referred to that point." [8] The Royal Navy used the additional "rule that quarter points were never read from a point beginning and ending with the same letter." [9]

Compass roses very rarely named the fractional points and only showed small, unlabelled markers as a guide for helmsmen.

128 compass directions

The table below shows how each of the 128 directions are named. The first two columns give the number of points and degrees clockwise from north. The third gives the equivalent bearing to the nearest degree from north or south towards east or west. The "CW" column gives the fractional-point bearings increasing in the clockwise direction and "CCW" counterclockwise. The final three columns show three common naming conventions: No "by" avoids the use of "by" with fractional points. Colour coding shows whether each of the three naming systems matches the "CW" or "CCW" column.

Traditional Mediterranean compass points

The traditional compass rose of eight winds (and its 16-wind and 32-wind derivatives) was invented by seafarers in the Mediterranean Sea during the Middle Ages (with no obvious connection to the twelve classical compass winds of the ancient Greeks and Romans). The traditional mariner's wind names were expressed in Italian, or more precisely, the Italianate Mediterranean lingua franca common among sailors in the 13th and 14th centuries, which was principally composed of Genoese (Ligurian), mixed with Venetian, Sicilian, Provençal, Catalan, Greek and Arabic terms from around the Mediterranean basin.

32-wind compass with traditional names (and traditional colour code) 32-point compass (traditional winds).svg
32-wind compass with traditional names (and traditional colour code)

This Italianate patois was used to designate the names of the principal winds on the compass rose found in mariners' compasses and portolan charts of the 14th and 15th centuries. The "traditional" names of the eight principal winds are:

Local spelling variations are far more numerous than listed, e.g. Tramutana, Gregale, Grecho, Sirocco, Xaloc, Lebeg, Libezo, Leveche, Mezzodi, Migjorn, Magistro, Mestre, etc. Traditional compass roses will typically have the initials T, G, L, S, O, L, P, and M on the main points. Portolan charts also colour-coded the compass winds: black for the eight principal winds, green for the eight half-winds, and red for the sixteen quarter-winds.

Each half-wind name is simply a combination of the two principal winds that it bisects, with the shortest name usually placed first, for example: NNE is "Greco-Tramontana"; ENE is "Greco-Levante"; SSE is "Ostro-Scirocco", etc. The quarter winds are expressed with an Italian phrase, "Quarto di X verso Y" (pronounced  [ˈkwarto di X ˈvɛrso Y] [10] [11] [12] one quarter from X towards Y), or "X al Y" (X to Y) or "X per Y" (X by Y). There are no irregularities to trip over; the closest principal wind always comes first, the more distant one second, for example: north-by-east is "Quarto di Tramontana verso Greco"; and northeast-by-north is "Quarto di Greco verso Tramontana".

The table below shows how the 32 compass points are named. Each point has an angular range of 11+14 degrees where the azimuth midpoint is the horizontal angular direction (clockwise from north) of the given compass bearing; minimum is the lower (counterclockwise) angular limit of the compass point; and maximum is the upper (clockwise) angular limit of the compass point.

Chinese compass points

Navigation texts dating from the Yuan, Ming, and Qing dynasties in China use a 24-pointed compass with named directions. These are based on the twelve Earthly Branches, which also form the basis of the Chinese zodiac. When a single direction is specified, it may be prefaced by the character (meaning single) or .

Ming Dynasty 24-pointed compass Ming-marine-compass.jpg
Ming Dynasty 24-pointed compass

Headings mid-way in-between are compounds as in English. For instance, 癸子 refers to the direction halfway between point and point , or 7+12°. This technique is referred to as a double-needle (雙針) compass.

PointOrdinal NameAngle
north0° or 360°
guǐ15°
chǒu30°
gěnnortheast45°
yín60°
jiǎ75°
mǎoeast90°
105°
chén120°
xùnsoutheast135°
150°
bǐng165°
south180°
dīng195°
wèi210°
kūnsouthwest225°
shēn240°
gēng255°
yǒuwest270°
xīn285°
300°
qiánnorthwest315°
hài330°
rén345°

See also

Related Research Articles

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References

  1. Evans, Frederick John, ed. (1859). "Notes on the Magnetism of Ships". Pamphlets on British shipping. 1785–1861. p. 8 (p. 433 of PDF). ISBN   0-217-85167-3. A deviation table having been formed by any of the processes now so generally understood, either on the thirty-two points of the compass, the sixteen intermediate, or the eight principal points
  2. Boardman, David (1983). Graphicacy and Geography Teaching. p. 41. In particular they should learn that wind direction is always stated as the direction from which, and not to which, the wind is blowing. Once children have grasped these eight points they can learn the full sixteen points of the compass.
  3. 1 2 See Wiktionary definitions: north; northeast; east; southeast; south; southwest; west; northwest
  4. Webb Aintablian, Xanthe (June 28, 2018). "An Overview and History of the Compass". thoughtco.com. Dotdash. Archived from the original on July 6, 2018.
  5. Lee, Robert E. (2011). "Compass Rose". University of Washington. Archived from the original on February 21, 2015.
  6. George Payn Quackenbos A Natural Philosophy: Embracing the Most Recent Discoveries 1860 "Mentioning the mariner's compass: the points of the compass in their order is called boxing the compass. — The compass box is suspended within a larger box by means of two brass hoops, or gimbals as they are called, supported at opposite ..."
  7. E. Chambers Cyclopaedia: or, an Universal Dictionary of Arts and Science, 5th Ed, 1743, pp. 206–7, "Points of the Compass, or Horizon, &c., in Geography and Navigation, are the points of division when the whole circle, quite around, is divided into 32 equal parts. These points are therefore at the distance of the 32d part of the circuit, or 11°15′, from each other; hence 5°37+1/2′ is the distance of the half points and 2°48+3/4′ is the distance of the quarter points.
  8. Bowditch, Nathaniel (1916). American Practical Navigator: An Epitome of Navigation and Nautical Astronomy. United States Hydrographic Office. p.  15.
  9. Kemp, Peter, ed. (1988). "Box the Compass". The Oxford Companion to Ships and the Sea. Oxford University Press. p.  103. ISBN   0-19-282084-2.
  10. "quarto". WordReference.com. Retrieved December 2, 2018. English translation: fourth, quarter
  11. "di". WordReference.com. Retrieved December 2, 2018. English translation: of, from...
  12. "verso". WordReference.com. Retrieved December 2, 2018. English translation: towards, toward, close to, near to