Cardinal direction



The four cardinal directions or cardinal points are north, south, east, and west, commonly denoted by their initials - N, S, E, W. They are mostly used for geographic orientation on Earth but may be calculated anywhere on a rotating astronomical body. North and south point toward the geographical poles defined by the axis of rotation, such that the body appears to rotate counter-clockwise when viewed from above the north pole. East and west are at right angles to north and south, with east being in the direction of rotation and west being directly opposite. Intermediate points between the four cardinal directions form the points of the compass. The intermediate directions are north-east (NE), north-west (NW), south-west (SW), and south-east (SE).

On Earth, upright observers facing north will have south behind them, east on their right, and west on their left. Most devices and methods for orientation therefore operate by finding north first, although any other direction is equally valid, if it can be reliably located. Several of these devices and methods are described below.

Compass
A magnetic compass is used to locate the cardinal directions to a good approximation. Compasses use the fact that the axis of the Earth's magnetic field is closely aligned with its axis of rotation. In its simplest form, a magnetised needle that is free to rotate about its axis will always point toward north. This is taken to be the same as geographic north. This approximation becomes less accurate the closer one gets to either of the magnetic poles. Compasses are also affected by local magnetic fields, which may result from geographic features such as mountains, ore bodies beneath the surface, or nearby metal equipment, especially if it is electrically powered and unshielded. They are, of course, also affected by magnets including that of another nearby compass needle.

A simple compass can be made by floating a magnetized needle on a leaf in a dish of water.

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 in the east and tracks upwards. In the evening it sets in the west. In the middle of the day it is to the south for viewers in the Northern Hemisphere and the north for those in the Southern Hemisphere. 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. (See seasons and solstice for more on this).

Therefore, a more accurate fix can be made if the time of year and approximate latitude are factored in. It should also be noted that, due to the Earth's axial tilt, no matter what your location, 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 March equinox to the September equinox, and rise south of east (and set south of west) from the September equinox to the March equinox.

It should also be noted that 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.

The apparent motion of the Sun is more reliable than its position. If a straight stick is planted in the ground so that it has no visible shadow, as the Sun moves (westward) a shadow will appear pointing due east. This works at any latitude.

Watch face
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 relatively minor inaccuracies due to the difference between local time and zone time, and due to the equation of time. The method functions less well as you get closer to the equator.

The photograph shows a specialized 24-hour watch designed for finding directions using the Sun 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.

Nighttime stars
Astronomy provides a more reliable method for finding direction at night. The Earth's axis is currently (but not permanently) pointed, to within a fraction of 1 degree, toward the bright star Polaris. The exact direction of the axis changes over thousands of years due to the precession of the equinoxes. We call the end of the Earth's axis that points to Polaris the North Pole. The opposite end of the axis is named the South Pole. 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.

Picking out a specific single star may leave one uncertain they've found the right one. As an aid to identifying Polaris, the asterism "Big Dipper" may be employed. The 2 corner stars of the "pan" (those opposite from the handle) point above the top of the "pan" to Polaris. This is illustrated at this example, the beginning of a tutorial that teaches how to find Polaris. To see the rest of the tutorial click the link at the bottom of the illustration.

From the Southern Hemisphere, nightly observations of the sky directly above the vicinity of the true pole will reveal that the visible stars appear to be moving in a circular path. (It is actually the observer that is moving in the circular path.) This becomes completely obvious when a special case of long exposure photography is employed to record the observations, 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. The common center is exactly aligned with the true (as opposed to the magnetic) pole. (This also is true of the northern hemisphere, and can be used to verify one has correctly identified Polaris, which will not appear to move.) A published photograph exposed for nearly 8 hours demonstrates this effect.

Inertial navigation
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 ship use in scenarios where the magnetic compass simply wasn't good enough. It has the further advantages of immunity to interference by stray magnetic fields, and not depending on Earth's magnetic field at all. 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. GPRS 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 must be moving, typically at more than 0.1 mph (0.2 km/h), to correctly display compass directions. 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:
 * North (N): 0° = 360°
 * East (E): 90°
 * South (S): 180°
 * West (W): 270°

An ordinal, or intercardinal, or intermediate, direction is one of the four intermediate compass directions located halfway between the cardinal directions.
 * Northeast (NE), 45°, halfway between north and east, is the opposite of southwest.
 * Southeast (SE), 135°, halfway between south and east, is the opposite of northwest.
 * Southwest (SW), 225°, halfway between south and west, is the opposite of northeast.
 * Northwest (NW), 315°, halfway between north and west, is the opposite of southeast.

These 8 words have been further compounded, resulting in a total of 32 named (and numbered) points evenly spaced around the compass. Some languages do not use compound words to name the points, instead assigning unique words, colors, and/or associations with phenomena of the natural world.

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. Portable GPS-based navigation computers 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 their 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
Children are sometimes taught the order of these directions (clockwise, from North) by using a mnemonic, such as "Naughty Elephants Squirt Water," "Never Eat Soggy Waffles", "Never Eat Shredded Wheat" ("Soggy Weet-Bix" in Australia & New Zealand), "Never Enter Stinky Washroom, "Never Eat Slimy Worms," or "Never Eat Sour Watermelon," or "Never Eat Sea Weed." Also, "West and East spell WE."

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.

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.
 * north (Proto-Germanic *norþ-) from a root *ner- "left, below", i.e. "to the left of the rising Sun".
 * east (*aus-to-) from the word for dawn, see Ēostre.
 * south (*sunþ-) is root-cognate to Sun itself, thus "the region of the Sun"
 * west (*wes-t-) from a word for "evening", root-cognate to Latin vesper.

Cardinal directions in world cultures
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 ordinal directions. The classical Greeks personified these winds as Anemoi. The article on boxing the compass contains a more recent list of directional winds from the Mediterranean Sea.

Far East
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.

Each direction is often identified with a color, and geographical or ethnic terms may contain the name of the color instead of the name of the corresponding direction. These traditions were also carried west by the westward migration of the Turkic peoples.

East: Green (青 "qīng" corresponds to green); 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 Sea: south of Turkey

West: White; Autumn; Metal
 * White Sheep Turkmen
 * Ak Deniz "White Sea" in Turkish indicates the Sea of Marmara, the Aegean Sea, or the Mediterranean Sea
 * Belarus (literally "White Russia"), according to one of the theories is the name given to the Western Rus by the Mongols

North: Black; Winter; Water
 * Heilongjiang "Black Dragon River" province in Northeast China, also the Amur River
 * Black Sea: north of Turkey
 * Kara-Khitan Khanate

Center: Yellow; Earth
 * Mount Huang "Yellow Mountain" in central China
 * Golden Horde: "Central Army" of the Mongols

Americas
In Mesoamerica and North America, many traditional indigenous beliefs include four cardinal directions and a center. Each direction was associated with a color, which varied between groups but which generally corresponded to the hues of corn (green, black, red, white, and yellow). There seems to be no “preferred” way of assigning these colors; as shown in the table, great variety in color symbolism occurs even among cultures that are close neighbors geographically.

Unique (non-compound) names of ordinal directions
In some languages, such as Finnish, Estonian and Breton, the ordinal 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).

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.