Cardinal direction

"Cardinal point" redirects here. For other uses, see Cardinal point (disambiguation).
A compass rose showing the four cardinal directions, the four intercardinal directions, plus eight further divisions.

The four cardinal directions or cardinal points are the directions of north, east, south, and west, commonly denoted by their initials: N, E, S, W. East and west are at right angles to north and south, with east being in the clockwise direction of rotation from north and west being directly opposite east. Intermediate points between the four cardinal directions form the points of the compass. The intermediate (intercardinal, or ordinal) directions are northeast (NE), southeast (SE), southwest (SW), and northwest (NW). Further, the intermediate direction of every set of intercardinal and cardinal direction is called a secondary-intercardinal direction, the eight shortest points in the compass rose to the right, i.e. NNE, ENE, ESE, and so on.

Locating the directions

Direction versus bearing

Latitude circles near the North Pole are shown in red. For A and B to face each other, A has to look East but B not to the West. If B were to look West, she would see a bear eyeing her as his next meal. For A and C to face each other, both would have to face North.

To keep to a bearing is not, in general, the same as going in a straight direction along a great circle. Conversely, one can keep to a great circle and the bearing may change. Thus the bearing of a straight path crossing the North Pole changes abruptly at the Pole from North to South. When travelling East or West, it is only on the Equator that one can keep East or West and be going straight (without need to steer). Anywhere else, maintaining latitude requires a change in direction, requires steering. However, this change in direction becomes increasingly negligible as one moves to lower latitudes.

Magnetic compass

Main article: Compass

The Earth has a magnetic field which is approximately aligned with its axis of rotation. A magnetic compass is a device that uses this field to determine the cardinal directions. Magnetic compasses are extremely widely used, but only moderately accurate.

The Sun

The position of the Sun in the sky can be used for orientation if the general time of day is known. In the morning, the Sun rises roughly in the east (due east only on the equinoxes) and tracks upwards. In the evening it sets in the west, again roughly and only due west exactly on the equinoxes. In the middle of the day it is to the south for viewers in the Northern Hemisphere, who live north of the Tropic of Cancer, and the north for those in the Southern Hemisphere, who live south of the Tropic of Capricorn. This method works less well closer to the equator (i.e. between the Tropic of Cancer and the Tropic of Capricorn) since, in the northern hemisphere, the sun may be directly overhead or even to the north in summer. Conversely, at low latitudes in the southern hemisphere the sun may be to the south of the observer in summer. In these locations, one needs first to determine whether the sun is moving from east to west through north or south by watching its movements—left to right means it is going through south while right to left means it is going through north; or one can watch the sun's shadows. If they move clockwise, the sun will be in the south at midday, and if they move anticlockwise, then the sun will be in the north at midday.

Due to the Earth's axial tilt, no matter what the location of the viewer, there are only two days each year when the sun rises precisely due east. These days are the equinoxes. On all other days, depending on the time of year, the sun rises either north or south of true east (and sets north or south of true west). For all locations the sun is seen to rise north of east (and set north of west) from the Northward equinox to the Southward equinox, and rise south of east (and set south of west) from the Southward equinox to the Northward equinox.

A more accurate fix can be made if the time of year and approximate latitude are factored in. The amount that the sun appears to be either north or south depends on both the time of year and latitude of the observer. Knowing these will enable the observer to be more precise when determining the cardinal directions from the sun's position, particularly in the early morning or late afternoon.

Watch face

A method to identify north and south directions using the sun and a 12-hour analogue clock or watch set to the local time, 10:10 a.m. in this example.

There is a traditional method by which an analog watch can be used to locate north and south. The Sun appears to move in the sky over a 24-hour period while the hour hand of a 12-hour clock face takes twelve hours to complete one rotation. In the northern hemisphere, if the watch is rotated so that the hour hand points toward the Sun, the point halfway between the hour hand and 12 o'clock will indicate south. For this method to work in the southern hemisphere, the 12 is pointed toward the Sun and the point halfway between the hour hand and 12 o'clock will indicate north. During daylight saving time, the same method can be employed using 1 o'clock instead of 12. There are minor inaccuracies due to the difference between local time and zone time, and due to the equation of time. Corrections can be made for these errors.

Specialized 24-hour watch with compass card dial

This method assumes that the azimuth (compass bearing) of the Sun changes at a constant rate throughout the day. Strictly, this is true only if the observer is at one of the Earth's poles. Close to the equator, the Sun's azimuth changes at very different speeds at different times of day, and even sometimes reverses direction. (See footnote[lower-alpha 1] for examples.) This completely invalidates this method of using a watch as a compass in tropical and low-temperate latitudes. However, at fairly high latitudes, more than about 50 degrees north or south, the speed of the Sun's change of azimuth is sufficiently constant to allow the method to be accurate enough for simple purposes. The method originated in the United Kingdom, which is almost entirely to the North of 50°N latitude. British Boy Scouts and Girl Guides frequently use it.

The photograph shows a specialized 24-hour watch designed for finding directions using the Sun at high latitudes in the northern hemisphere. With the watch set to indicate local time, the hour hand is pointed directly at the Sun. North is then indicated by the local midnight position.

Sundial

A portable sundial can be used as a more accurate instrument than a watch for determining the cardinal directions. Since the design of a sundial takes account of the latitude of the observer, it can be used at any latitude. See: Sundial#Using a sundial as a compass.

Astronomy

Astronomy provides a method for finding direction at night. All the stars appear to lie on the imaginary Celestial sphere. Because of the rotation of the Earth, the Celestial Sphere appears to rotate around an axis passing through the North and South poles of the Earth. This axis intersects the Celestial Sphere at the North and South Celestial poles, which appear to the observer to lie directly above due North and South respectively on the horizon.

In either hemisphere, observations of the night sky show that the visible stars appear to be moving in circular paths, caused by the rotation of the Earth. This is best seen in a long exposure photograph, which is obtained by locking the shutter open for most of the intensely dark part of a moonless night. The resulting photograph reveals a multitude of concentric arcs (portions of perfect circles) from which the exact center can be readily derived, and which corresponds to the Celestial pole, which lies directly above the position of the true pole (North or South) on the horizon. A published photograph exposed for nearly 8 hours demonstrates this effect.

The Northern Celestial pole is currently (but not permanently) within a fraction of 1 degree of the bright star Polaris. The exact position of the pole changes over thousands of years due to the precession of the equinoxes. Polaris is also known as the North Star, and is generically called a pole star or lodestar. Polaris is only visible during fair weather at night to inhabitants of the Northern Hemisphere. The asterism "Big Dipper" may be used to find Polaris. The 2 corner stars of the "pan" (those opposite from the handle) point above the top of the "pan" to Polaris.

While observers in the Northern hemisphere can use the star Polaris to determine the Northern celestial pole, the Octans constellation's South Star is hardly visible enough to use for navigation. For this reason, the preferred alternative is to use the constellation Crux (The Southern Cross). The southern celestial pole lies at the intersection of (a) the line along the long axis of crux (i.e. through Alpha Crucis and Gamma Crucis) and (b) a line perpendicularly bisecting the line joining the "Pointers" (Alpha Centauri and Beta Centauri).

Gyrocompass

At the very end of the 19th century, to avoid the need to wait for fair weather at night to precisely verify one's alignment with true north, the gyrocompass was developed for shipboard use. Since it finds true, rather than magnetic, north, it is immune to interference by local or shipboard magnetic fields. Its major disadvantage is that it depends on technology that many individuals might find too expensive to justify outside the context of a large commercial or military operation. It also requires a continuous power supply for its motors, and that it be allowed to sit in one location for a period of time while it properly aligns itself.

Satellite navigation

Near the end of the 20th century, the advent of satellite-based Global Positioning Systems (GPS) provided yet another means for any individual to determine true north accurately. While GPS Receivers (GPSRs) function best with a clear view of the entire sky, they function day or night, and in all but the most severe weather. The government agencies responsible for the satellites continuously monitor and adjust them to maintain their accurate alignment with the Earth. There are consumer versions of the receivers that are attractively priced. Since there are no periodic access fees, or other licensing charges, they have become widely used. GPSR functionality is becoming more commonly added to other consumer devices such as mobile phones. Handheld GPSRs have modest power requirements, can be shut down as needed, and recalibrate within a couple of minutes of being restarted. In contrast with the gyrocompass which is most accurate when stationary, the GPS receiver, if it has only one antenna, must be moving, typically at more than 0.1 mph (0.2 km/h), to correctly display compass directions. On ships and aircraft, GPS receivers are often equipped with two or more antennas, separately attached to the vehicle. The exact latitudes and longitudes of the antennas are determined, which allows the cardinal directions to be calculated relative to the structure of the vehicle. Within these limitations GPSRs are considered both accurate and reliable. The GPSR has thus become the fastest and most convenient way to obtain a verifiable alignment with the cardinal directions.

Additional points

The directional names are also routinely and very conveniently associated with the degrees of rotation in the unit circle, a necessary step for navigational calculations (derived from trigonometry) and/or for use with Global Positioning Satellite (GPS) receivers. The four cardinal directions correspond to the following degrees of a compass:

An intercardinal, or ordinal, or intermediate, direction is one of the four intermediate compass directions located halfway between the cardinal directions.

These 8 words have been further compounded, resulting in a total of 32 named points evenly spaced around the compass: north (N), north by east (NbE), north-northeast (NNE), northeast by north (NEbN), northeast (NE), northeast by east (NEbE), east-northeast (ENE), east by north (EbN), east (E), etc.

Usefulness of cardinal points

With the cardinal points thus accurately defined, by convention cartographers draw standard maps with north (N) at the top, and east (E) at the right. In turn, maps provide a systematic means to record where places are, and cardinal directions are the foundation of a structure for telling someone how to find those places.

North does not have to be at the top. Most maps in medieval Europe, for example, placed east (E) at the top.[1] A few cartographers prefer south-up maps. Many portable GPS-based navigation computers today can be set to display maps either conventionally (N always up, E always right) or with the current instantaneous direction of travel, called the heading, always up (and whatever direction is +90° from that to the right).

The direction of travel required to reach the intended destination is called the bearing. Since the real world presents numerous obstacles, a person must adjust his or her heading accordingly. Upon moving forward, the bearing will change so that it always points at the destination, thereby giving clues as to which way to turn. When travelling, it is often easier to work out where the next turn is, and whether to turn left or right, when the direction of travel is always up.

Beyond geography

In mathematics, cardinal directions or cardinal points are the six principal directions or points along the x-, y- and z-axis of three-dimensional space.

In the real world there are six cardinal directions not involved with geography which are north, south, east, west, up and down. In this context, up and down relate to elevation, altitude, or possibly depth (if water is involved). The topographic map is a special case of cartography in which the elevation is indicated on the map, typically via contour lines.

In astronomy, cardinal points of the disk of an astronomical body may be four points defined by the direction in which the celestial poles are located, as seen from the center of the disk.[2][3]

A line (here it is a great circle on the celestial sphere) drawn from the center of the disk to the North celestial pole will intersect the body's limb at the North point. Similarly, a line from the center to the South celestial pole will define the South point by its intersection with the limb. The points at right angles to the North and South points are the East and West points. The North point will then be the point on the limb that is closest to the North celestial pole.

Germanic origin of names

During the Migration Period, the Germanic languages' names for the cardinal directions entered the Romance languages, where they replaced the Latin names borealis (or septentrionalis) with north, australis (or meridionalis) with south, occidentalis with west and orientalis with east. It is possible that some northern people used the Germanic names for the intermediate directions. Medieval Scandinavian orientation would thus have involved a 45 degree rotation of cardinal directions.[4]

Cardinal directions in world cultures

Europe N E S W C Source
Slavic — [10]

Many cultures not descended from European traditions use cardinal directions, but have a number other than four. Typically, a “center” direction is added, for a total of five. Rather than the Western use of direction letters, properties such as colors are often associated with the various cardinal directions—these are typically the natural colors of human perception rather than optical primary colors. Some examples are shown here. In many regions of the world, prevalent winds change direction seasonally, and consequently many cultures associate specific named winds with cardinal and intercardinal directions. The classical Greeks personified these winds as Anemoi. When boxing the compass into intercardinal subdirections, each corresponds to one of the directional winds into the Mediterranean Sea (for example, south-east is linked to Sirocco, the wind from the Sahara).

Arabic language

Countries where Arabic is used refer to the cardinal directions as Ash Shamaliyah (N), Al Gharbiyah (W), Ash Sharqiyah (E) and Al Janobiyah (S). Additionally, Al Wusta is used for the center. All five are used for geographic subdivision names (wilayahs, states, regions, governorates, provinces, districts or even towns), and some are the origin of some Southern Iberian place names (such as Algarve, Portugal and Axarquía, Spain).

Far East

Asia N E S W C Source
China [11][12]
Ainu [13][14]
Turkic [13]
Kalmyks — [15]
Tibet [13]

Dynastic Chinese culture and some other Central Asian cultures view the center as a fifth principal direction hence the English translated term "Five Cardinal Points". Where it is different than the west, is that the term is used as a foundation for I Ching, the Wu Xing and the five naked-eye planets.

In traditional Chinese astrology, the zodiacal belt is divided into the four constellation groups corresponding to the four cardinal directions.

Each direction is often identified with a color, and (at least in China) with a mythological creature of that color. Geographical or ethnic terms may contain the name of the color instead of the name of the corresponding direction.[11][12]

East: Green (青 "qīng" corresponds to both green and blue); Spring; Wood

Qingdao (Tsingtao) "Green Island": a city on the east coast of China

South: Red; Summer; Fire

Red River (Asia): south of China
Red Croatia
Red Ruthenia

West: White; Autumn; Metal

White Sheep Turkmen
Akdeniz, meaning White Sea: Mediterranean Sea in Turkish
Belarus, meaning White Rus' or White Ruthenia
White Serbia
White Croatia

North: Black; Winter; Water

Heilongjiang "Black Dragon River" province in Northeast China, also the Amur River
Kara-Khitan Khanate "Black Khitans" who originated in Northern China
Black Sea: north of Anatolia
Black Ruthenia

Center: Yellow; Earth

Huangshan "Yellow Mountain" in central China
Golden Horde: "Central Army" of the Mongols

Americas

In Mesoamerica and North America, a number of traditional indigenous cosmologies include four cardinal directions and a center. Some may also include "above" and "below" as directions, and therefore focus on a cosmology of seven directions. Each direction may be associated with a color, which can vary widely between nations, but which is usually one of the basic colors found in nature and natural pigments, such as black, red, white, and yellow, with occasional appearances of blue, green, or other hues.[16] In some cases, e.g., many of the Puebloan peoples of the Southwestern United States, the four named directions are not North, South, East and West but are the four intermediate directions associated with the places of sunrise and sunset at the winter and summer solstices.[17][18] There can be great variety in color symbolism, even among cultures that are close neighbors geographically.

Australia

Some indigenous Australians have cardinal directions deeply embedded in their culture. For example, the Warlpiri people have a cultural philosophy deeply connected to the four cardinal directions[19] and the Guugu Yimithirr people use cardinal directions rather than relative direction even when indicating the position of an object close to their body (see Use of cardinal direction instead of relative direction).

The precise direction of the cardinal points appears to be important in Aboriginal stone arrangements.

Many aboriginal languages contain words for the usual four cardinal directions, but some contain words for 5 or even 6 cardinal directions.[20]

Unique (non-compound) names of intercardinal directions

In some languages, such as Finnish, Estonian and Breton, the intercardinal directions have names that are not compounds of the names of the cardinal directions (as, for instance, northeast is compounded from north and east). In Finnish those are koillinen (northeast), kaakko (southeast), lounas (southwest), and luode (northwest). Compare with the non-compound names used for the numbers 11–19 in English (eleven, rather than *ten-one) and special names for one and a half and two and a half in many languages of India, such as Hindi and Marathi. In Japanese, there is the interesting situation that native Japanese words (yamato kotoba, kun readings of kanji) are used for the cardinal directions (such as minami for 南, south), but borrowed Chinese words (on readings of kanji) are used for intercardinal directions (such as tō-nan for 東南, southeast, lit. "east-south"). In the Malay language, adding laut (sea) to either east (timur) or west (barat) results in northeast or northwest, respectively, whereas adding daya to west (giving barat daya) results in southwest. However, southeast has a special word: tenggara.

Sanskrit and other Indian languages that borrow from it use the names of the gods associated with each direction: east (Indra), southeast (Agni), south (Yama/Dharma), southwest (Nirrti), west (Varuna), northwest (Vayu), north (Kubera/Heaven) and northeast (Ishana/Shiva). North is associated with the Himalayas and heaven while the south is associated with the underworld or land of the fathers (Pitr loka). The directions are named by adding "disha" to the names of each god or entity: e.g. Indradisha (direction of Indra) or Pitrdisha (direction of the forefathers i.e. south).

The Hopi language and the Tewa dialect spoken by the Arizona Tewa have proper names for the solstitial directions, which are approximately intercardinal, rather than for the cardinal directions.[21][22]

Non-compass directional systems

Use of the compass directions is common and deeply embedded in European culture, and also in Chinese culture (see south-pointing chariot). Some other cultures make greater use of other referents, such as towards the sea or towards the mountains (Hawaii, Bali), or upstream and downstream (most notably in ancient Egypt, also in the Yurok and Karuk languages). Lengo (Guadalcanal, Solomon Islands) has four non-compass directions: landward, seaward, upcoast, and downcoast.

See also

Notes

  1. ↑ The direction appears to reverse when the Sun is viewed close to the local summer solstice from places within the tropics, but not exactly on the equator. In the Northern Hemisphere, the Sun appears to rise at a point on the horizon well to the north of east. During the early morning, its azimuth moves clockwise so the Sun is close to due east soon before noon. Then the change of azimuth reverses direction to anticlockwise, so the Sun passes to the north of the zenith at noon, Another reversal occurs in the afternoon, so the Sun's azimuth moves clockwise from roughly west to its setting point to the north of west. The directions are opposite in the Southern Hemisphere. In another extreme case, seen from the equator at an equinox, the Sun appears to rise vertically from the eastern horizon to the zenith, so for several hours its azimuth does not change. The Sun is due east all morning. Then, as it appears to pass directly overhead at noon, its azimuth abruptly changes by 180 degrees, from due east to due west. Following that, the Sun appears to descend vertically, at a constant azimuth of due west, to the western horizon.

References

  1. ↑ Snyder's Medieval Art, 2nd ed. (ed. Luttikhuizen and Verkerk; Prentice Hall, 2006), pp. 226-7.
  2. ↑ Rigge, W. F. "Partial eclipse of the moon, 1918, June 24". Popular Astronomy 26: 373. Bibcode:1918PA.....26..373R. rigge1918
  3. ↑ Meadows, Peter; meadows. "Solar Observing: Parallactic Angle". Retrieved 2013-11-15.
  4. ↑ 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.
  5. ↑ entries 765-66 of the Indogermanisches etymologisches Wörterbuch
  6. ↑ entries 86-7 of the Indogermanisches etymologisches Wörterbuch
  7. ↑ entries 914-15 of the Indogermanisches etymologisches Wörterbuch
  8. ↑ entries 1173 of the Indogermanisches etymologisches Wörterbuch
  9. ↑ entries 86-7 of the Indogermanisches etymologisches Wörterbuch
  10. ↑ Ukrainian Soviet Encyclopedic dictionary, Kiev, 1987.
  11. 1 2 "Cardinal colors in Chinese tradition". Retrieved 2007-02-17.
  12. 1 2 "Chinese Cosmogony". Retrieved 2007-02-17.
  13. 1 2 3 "Colors of the Four Directions". Retrieved 2010-05-16.
  14. ↑ "Two Studies of Color". Retrieved 2008-03-14. In Ainu... siwnin means both 'yellow' and 'blue' and hu means 'green' and 'red'
  15. ↑ Krupp, E. C.: "Beyond the Blue Horizon: Myths and Legends of the Sun, Moon, Stars, and Planets", page 371. Oxford University Press, 1992
  16. ↑ Anderson, Kasper Wrem; Helmke, Christophe (2013), "The Personifications of Celestial Water: The Many Guises of the Storm God in the Pantheon and Cosmology of Teotihuacan", Contributions in New World Archaeology 5: 165–196, at pp. 177-179.
  17. ↑ McCluskey, Stephen C. (2014), "Hopi and Puebloan Ethnoastronomy and Ethnoscience", in Ruggles, Clive L. N., Handbook of Archaeoastronomy and Ethnoastronomy, New York: Springer Science+Business Media, pp. 649–658, doi:10.1007/978-1-4614-6141-8_48, ISBN 978-1-4614-6140-1
  18. ↑ Curtis, Edward S. (1922), Hodge, Frederick Webb, ed., The Hopi, The North American Indian 12, Norwood, Mass.: The Plimpton Press, p. 246, retrieved 23 Aug 2014, Hopi orientation corresponds only approximately with ours, their cardinal points being marked by the solstitial rising and setting points of the sun.... Their cardinal points therefore are not mutually equidistant on the horizon and agree roughly with our semi-cardinal points.
  19. ↑ ``Ngurra-kurlu: A way of working with Warlpiri people Pawu-Kurlpurlurnu WJ, Holmes M and Box L. 2008, Desert Knowledge CRC Report 41, Alice Springs
  20. ↑ Orientations of linear stone arrangements in New South Wales Hamacher et al., 2013, Australian Archaeology, 75, 46-54
  21. ↑ Stephen, Alexander MacGregor (1936), Parsons, Elsie Clews, ed., Hopi Journal of Alexander M. Stephen, Columbia University Contributions to Anthropology 23, New York: Columbia University Press, pp. 1190–1191, OCLC 716671864
  22. ↑ Malotki, Ekkehart (1979), Hopi-Raum: Eine sprachwissenschaftliche Analyse der Raumvorstellungen in der Hopi-Sprache, Tübinger Beiträge zur Linguistik (in German) 81, Tübingen: Gunter Narr Verlag, p. 165, ISBN 3-87808-081-6
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