Science Fair Project Encyclopedia
- For the term that denotes the wealthy and powerful "North" of the world, see: "The North".
North is one of the four primary cardinal directions, specifically the direction that, in Western culture, is treated as the primary direction and used (explicitly or implicitly) to define all other directions. (As to the arbitrary nature of this choice, and psycho-social consequences of it, see boreocentrism .)
North can mean:
- true north, the direction along the earth's surface toward one pole of the earth's rotation, namely the pole that is clearly on one's left when standing at the Equator while facing the rising sun.
- magnetic north, the direction along the earth's surface in which horizontal magnetic field strength has its most positive value (but see Flipping of planetary magnetic poles for an eventual event, so rare as to make unlikely any advance agreement on whether one or two retronyms would be involved in the replacement terminology)
- a loosely specified direction, usually within half a right angle of true north, especially when stating travel instructions in an area where directions of travel are constrained by an approximately rectangular grid of streets, hallways, etc.; this is often called 'grid north' or 'plan north'.
- the orientation of a traveller with respect to a visible or otherwise definite continuous two-way route, such that sustained travel over the whole of the route produces a change of position to a location further north, even if that involves travelling a part of the route in another direction, even straight south; often termed "northbound".
- pertaining to the part of a route mainly or exclusively used by northbound traffic, where southbound traffic is separated by barriers, or where both are encouraged to stay mostly in one portion by rules of the road; often termed "northbound".
Magnetic north and declination
Magnetic north is of interest because it is the direction indicated as north on a properly functioning (but uncorrected) magnetic compass. The difference between it and true north is called the magnetic declination (or simply the declination where the context is clear). For many purposes and physical circumstances, the error in direction that results from ignoring the distinction is tolerable; in others a mental or instrument compensation, based on assumed knowledge of the applicable declination, can solve all the problems. But simple generalizations on the subject should be treated as unsound, and as likely to reflect popular misconceptions about terrestrial magnetism .
Roles of north as prime direction
The visible rotation of the night sky about the visible celestial pole provides a vivid metaphor of that direction corresponding to up. Thus the choice of the north as corresponding to up in the northern hemisphere, or of south in that role in the southern, is, prior to world-wide communication, anything but an arbitrary one. On the contrary, it is of interest that Chinese culture ever considered south as the proper top end for maps.
In Western culture (unless making a point about harmful effects, or the arbitrary nature, of boreocentrism):
- Up is a metaphor for north
- Maps tend to be drawn for viewing with either true north or magnetic north at the top (page layout)
- Globes of the earth have the North Pole at the top, or if the earth's axis is represented as inclined from vertical (normally by the angle it has relative to the axis of the earth's orbit), in the top half.
- Maps are usually labelled to indicate which direction on the map corresponds to a direction on the earth,
- usually with a single arrow oriented to the map's representation of true north,
- occasionally with a single arrow oriented to the map's representation of magnetic north, or two arrows oriented to true and magnetic north respectively,
- occasionally with a compass rose, but if so, usually on a map with north at the top and usually with north decorated more prominently than any other compass point.
Roles of east and west as inherently subsidiary directions
It is worth noting that while the choice of north over south as prime direction reflects quite arbitrary historical factors, east and west are not nearly as natural alternatives as first glance might suggest. Their folk definitions are, respectively, "where the sun rises" and "where it sets". Except on the Equator, however, these definitions, taken together, would imply that
- east and west would not be 180 degrees apart, but instead would differ from that by up to twice the degrees of latitude of the location in question, and
- they would each move slightly from day to day and, in the temperate zones, markedly over the course of the year.
Reasonably accurate folk astronomy, such as is usually attributed to Stone Age Celts, would arrive at east and west by noting the directions of rising and setting (preferably more than once each) and choosing as prime direction one of the two mutually opposite directions that lie halfway between those two. The true folk-astronomical definitions of east and west are "the directions, a right angle from the prime direction, that are closest to the rising and setting, respectively, of the sun (or moon).
- "The North", a sense of the term that refers to the wealthy and powerful "North" of the world, as contrasted to the poorer "South"
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details