how does a compass know weather its north south east or west?

Question

serious answers only from a well educated person

Answer 1

A compass (or mariner's compass) is a navigational instrument for finding directions on the earth. It consists of a magnetised pointer free to align itself accurately with Earth's magnetic field, which is of great assistance in navigation. The cardinal points are north, south, east and west. A compass can be used in conjunction with a clock and a sextant to provide a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient. The compass was developed in China more than seventeen hundred years ago, however the original inventor remains in dispute; legend has it was invented by emperor Huang Di.

A compass can be any magnetic device using a needle to indicate the direction of the magnetic north of a planet's magnetosphere. Any instrument with a magnetized bar or needle turning freely upon a pivot and pointing in a northerly and southerly direction can be considered a compass. A compass dial is a small pocket compass with a sundial. A variation compass is a specific instrument of a delicate type of construction. It is used by observing variations of the needle. A gyrocompass or astrocompass can also be used to ascertain True north.
Contents
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* 1 History of the navigational compass
* 2 Construction of a simple compass
* 3 Modern navigational compasses
* 4 Solid state compasses
* 5 Compass correction
* 6 Compass balancing
* 7 Points of the compass
* 8 See also
* 9 External links, resources, and references

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History of the navigational compass

The compass was invented in China; the earliest recorded use of lodestone as a direction finder was in a 4th century Chinese book: Book of the Devil Valley Master. The compass is considered one of the Four Great Inventions of Ancient China.

Dream Pool Essay written by Song Dynasty scholar Shen Kua in AD 1086 contained a detailed description of how geomancers magnetized a needle by rubbing its tip with lodestone, and hung the magnetic needle with one single strain of silk with a bit of wax attached to the center of the needle. Shen Kua pointed out that a needle prepared this way sometimes pointed south, sometimes north.

The earliest recorded use of a compass in navigation lies in Zhu Yu's book Pingzhou Ke Tan (Pingzhou Table Talks) of AD 1117.

The navigator knows the geography, he watches the stars at night, watches the sun at day; when it is dark and cloudy, he watches the compass

A pilot's compass handbook titled Shun Feng Xiang Song (Fair Winds for Escort) in the Oxford Bodleian Library contains great details about the use of compass in navigation.
Navigational mariner's compass
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Navigational mariner's compass

After this point there is much debate on what happened to the compass. Theories include its travel to the Middle East via the Silk Road, and then to Europe, direct transfer of the compass from China then Europe and then later from Europe to the Middle East, as well as independent creation of the compass in Europe and then its transfer thereafter to the Middle East. The latter 2 are supported by evidence of the Arabic word for "Compass" (al-konbas) possibly being a derivation of the old Italian word for compass. Other evidence for this includes the earlier mentioning of the compass in European works rather than Arabic. The first European mention of the directional compass occurs in Alexander Neckam's De naturis rerum (On the Natures of Things), probably written in Paris in 1190. As for the Arab world, Yemeni Sultan al-Ashraf appears to be the earliest confimed mention of the compass in 1290, though some authors assert an earlier recording, as early as 1242 for Arabic, and 1231 for Persian.

In China it seems that the convention was that the compass needle pointed south. Since the European convention has always been the opposite it has been suggested that independent invention may be more likely than cultural diffusion from China in this case.

Prior to the introduction of the compass, wayfinding at sea was primarily done via celestial navigation, supplemented in some places by the use of echo soundings. Difficulties arose where the sea was too deep for soundings and conditions were continually overcast or foggy. Thus the compass was not of the same utility everywhere. For example, the Arabs could generally rely on clear skies in navigating the Persian Gulf and the Indian Ocean (as well as the predictable nature of the monsoons). This may explain in part their relatively late adoption of the compass. Mariners in the relatively shallow Baltic made extensive use of soundings.

In the Mediterranean, however, the practice from ancient times had been to curtail sea travel between October and April, due in part to the lack of dependable clear skies during the Mediterranean winter (and much of the sea is too deep for soundings). With improvements in dead reckoning methods, and the development of better charts, this changed during the second half of the 13th century. By around 1290 the sailing season could start in late January or February, and end in December. The additional few months were of considerable economic importance; it enabled Venetian convoys, for instance, to make two round trips a year to the eastern Mediterranean, instead of one.

Around the time Europeans learned of the compass, traffic between the Mediterranean and northern Europe increased, and one factor may be that the compass made traversal of the Bay of Biscay safer and easier.
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Construction of a simple compass
A simple compass typical to a small yacht
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A simple compass typical to a small yacht

A magnetic rod is required when constructing a compass. This can be created by aligning an iron or steel rod with Earth's magnetic field and then tempering or striking it. However, this method produces only a weak magnet so other methods are preferred. This magnetised rod (or magnetic needle) is then placed on a low friction surface to allow it to freely pivot to align itself with the magnetic field. It is then labeled so the user can distinguish the north-pointing from the south-pointing end; in modern convention the north end is typically marked in some way, often by being painted red.

Flavio Gioja (fl. 1302), an Italian marine pilot, is sometimes credited with perfecting the sailor's compass by suspending its needle over a fleur-de-lis design, which pointed north. He also enclosed the needle in a little box with a glass cover.
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Modern navigational compasses
Liquid filled compass
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Liquid filled compass
A compass suitable for orienteering in the night
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A compass suitable for orienteering in the night

Modern navigational compasses hold a magnetized needle inside a fluid-filled capsule; the fluid causes the needle to stop quickly rather than oscillate back and forth around magnetic north. Other features common on modern handheld compasses are a baseplate with rulings for measuring distances on maps, a rotating bezel for measuring bearings of distant objects, and a sighting mirror that lets the user see both the compass needle and a distant object at the same time. Further, some modern compasses include an inclinometer for measuring gradients and are adjustable to account for varying Magnetic declination.

Mariner's compasses can have two or more magnetic needles permanently attached to a compass card. These move freely on a pivot. A lubber line, which can be a marking on the compass bowl or a small fixed needle indicates the ships heading on the compass card.

Traditionally the card is divided into thirty-two points (known as rhumbs), although modern compasses are marked in degrees rather than cardinal points. The glass-covered box (or bowl) contains a suspended gimbal within a binnacle. This preserves the horizontal position.

Large ships typically rely on a gyrocompass rather than a magnetic compass for navigation, and increasingly electronic fluxgate compasses are used on smaller vessels.

Compasses are available marked in mils - a unit of measurement commonly used by the military.
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Solid state compasses

Small compasses found in clocks and other electronic gear are Solid-state electronics usually built out of two or three magnetic field sensors that provide data for a microprocessor. Using Trigonometry the correct heading relative to the compass is calculated.

Often, the device is a discrete component which outputs either a digital or analog signal proportional to its orientation. This signal is interpreted by a controller or microprocessor and used either internally, or sent to a display unit. An example implementation, including parts list and circuit schematics, shows one design of such electronics. The sensor uses precision magnetics and highly calibrated internal electronics to measure the response of the device to the Earth's magnetic field. The electrical signal is then processed or digitized.
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Compass correction

Main article: Magnetic deviation

Ship's compass, with the two iron balls which correct the effects of non-ferromagnetic materials
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Ship's compass, with the two iron balls which correct the effects of non-ferromagnetic materials

A ship's compass must be corrected for errors, called compass deviation, caused by iron and steel in its structure and equipment. The ship is swung, that is rotated about a fixed point while its heading is noted by alignment with fixed points on the shore. A compass deviation card is prepared so that the navigator can convert between compass and magnetic headings. The compass can be corrected in three ways. First the lubber line can be adjusted so that it is aligned with the direction in which the ship travels, then the effects of permanent magnets can be corrected for by small magnets fitted within the case of the compass. The effect of non-ferromagnetic materials can be corrected by two iron balls mounted on either side of the compass binacle. The graph of the compass deviation can be understood using Fourier series. The coefficient a0 representing the error in the lubber line, while a1,b1 the ferromagnetic effects and a2,b2 the non-ferromagnetic component.

Fluxgate compasses can be calibrated automatically, and can also be programmed with the correct local compass variation so as to indicate the true heading.
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Compass balancing

Because Earth's magnetic field varies at different latitudes, compasses are often balanced during manufacture. Most manufacturers balance their compass needles for one of five zones, ranging from zone 1, covering most of the Northern Hemisphere, to zone 5 covering Australia and the southern oceans. This balancing prevents excessive dipping of one end of the needle which can cause the compass card to stick and give false readings.

Some different compass systems:
Compass with 400 grades division and conversion table
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Compass with 400 grades division and conversion table
Swiss army compass with mils division
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Swiss army compass with mils division
Land surveyor compass with clinometer
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Land surveyor compass with clinometer



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Points of the compass

Main article: Boxing the compass

The mariner's compass card is divided into thirty-two equally spaced points. Four of these - east, west, north, and south - are the cardinal points, and the names of the others are derived from these.

Answer 2

A compass is an extremely simple device. A magnetic compass (as opposed to a gyroscopic compass) consists of a small, lightweight magnet balanced on a nearly frictionless pivot point. The magnet is generally called a needle. One end of the needle is often marked "N," for north, or colored in some way to indicate that it points toward north. On the surface, that's all there is to a compass.


The reason why a compass works is more interesting. It turns out that you can think of the Earth as having a gigantic bar magnet buried inside. In order for the north end of the compass to point toward the North Pole, you have to assume that the buried bar magnet has its south end at the North Pole, as shown in the diagram at the right. If you think of the world this way, then you can see that the normal "opposites attract" rule of magnets would cause the north end of the compass needle to point toward the south end of the buried bar magnet. So the compass points toward the North Pole.

To be completely accurate, the bar magnet does not run exactly along the Earth's rotational axis. It is skewed slightly off center. This skew is called the declination, and most good maps indicate what the declination is in different areas (since it changes a little depending on where you are on the planet).

The magnetic field of the Earth is fairly weak on the surface. After all, the planet Earth is almost 8,000 miles in diameter, so the magnetic field has to travel a long way to affect your compass. That is why a compass needs to have a lightweight magnet and a frictionless bearing. Otherwise, there just isn't enough strength in the Earth's magnetic field to turn the needle.


The "big bar magnet buried in the core" analogy works to explain why the Earth has a magnetic field, but obviously that is not what is really happening. So what is really happening?

No one knows for sure, but there is a working theory currently making the rounds. As seen on the above, the Earth's core is thought to consist largely of molten iron (red). But at the very core, the pressure is so great that this superhot iron crystallizes into a solid. Convection caused by heat radiating from the core, along with the rotation of the Earth, causes the liquid iron to move in a rotational pattern. It is believed that these rotational forces in the liquid iron layer lead to weak magnetic forces around the axis of spin.

It turns out that because the Earth's magnetic field is so weak, a compass is nothing but a detector for very slight magnetic fields created by anything. That is why we can use a compass to detect the small magnetic field produced by a wire carrying a current (see How Electromagnets Work).

Creating Your Own Compass
If you don't have a compass, you can create your own in much the same way people did hundreds of years ago. To create your own compass, you will need the following materials:

* A needle or some other wire-like piece of steel (a straightened paper clip, for example)
* Something small that floats -- a piece of cork, the bottom of a Styrofoam coffee cup, a piece of plastic, the cap from a milk jug...
* A dish, preferably a pie plate, 9 to 12 inches (23 - 30 cm) in diameter, with about an inch (2.5 cm) of water in it

The first step is to turn the needle into a magnet. The easiest way to do this is with another magnet -- stroke the magnet along the needle 10 or 20 times as shown below.


If you are having trouble finding a magnet around the house, two possible sources include a can opener and an electromagnet that you make yourself (see How Electromagnets Work).

Place your float in the middle of your dish of water

The "float on water" technique is an easy way to create a nearly frictionless bearing. Center your magnetic needle on the float. It very slowly will point toward north. You have created a compass!

A magnetic compass like the one created on the previous page has several problems when used on moving platforms like ships and airplanes. It must be level, and it tends to correct itself rather slowly when the platform turns. Because of this tendency, most ships and airplanes use gyroscopic compasses instead.

A spinning gyroscope, if supported in a gimbaled frame and spun up, will maintain the direction it is pointing even if the frame moves or rotates. In a gyrocompass, this tendency is used to emulate a magnetic compass. At the start of the trip, the axis of the gyrocompass is pointed toward north using a magnetic compass as a reference. A motor inside the gyrocompass keeps the gyroscope spinning, so the gyrocompass will continue pointing toward north and will adjust itself swiftly and accurately even if the boat is in rough seas or the plane hits turbulence. Periodically, the gyrocompass is checked against the magnetic compass to correct any error it might pick up.

Answer 3

Is this a sreious question? Well, just in case it is, let me fill you very quickly. A traditional compass has a magnet which can freely rotate on an axis. A magnet reacts to magnetic force lines because of a physical force called electromagnetic force. The world happens to have a magnetic pole very close to the geographic north pole and another magnetic pole close to the geographic south pole. For most practical applications in navigation in mid lattitudes, the error is managable. This existence of magnetic poles is due to a specific motion of charged particles inside the earth's crust. These magnetic poles generate a magnetic force filed to which the magnet in your compass reacts to. When it does so, it alignes itself so that it lies on the north-south line.

Answer 4

the needle on the compass always points to magnetic north. It's done by the magnetic field of the earth and the field is stongest at the arctic or north pole

Answer 5

There is a magnet in the compass that points to true north.

Answer 6

there are magnets in the compass that point depending on which way you hold the compass in relation to magnetic north or magnetic south

Answer 7

because hte earth has a magnetic field and the compass pick up on it and turn to the it will tell u which direction is which

Answer 8

from the earths magnetic field and its relation to the north and south poles.