Compass

A compass is an instrument used for navigation and orientation that shows direction relative to the geographic cardinal directions (or points). Usually, a diagram called a compass rose shows the directions north, south, east, and west on the compass face as abbreviated initials. When the compass is used, the rose can be aligned with the corresponding geographic directions; for example, the "N" mark on the rose points northward. Compasses often display markings for angles in degrees in addition to (or sometimes instead of) the rose. North corresponds to 0°, and the angles increase clockwise, so east is 90° degrees, south is 180°, and west is 270°. These numbers allow the compass to show magnetic North azimuths or true North azimuths or bearings, which are commonly stated in this notation. If magnetic declination between the magnetic North and true North at latitude angle and longitude angle is known, then direction of magnetic North also gives direction of true North.

Among the Four Great Inventions, the magnetic compass was first invented as a device for divination as early as the Chinese Han Dynasty (since c. 206 BC),[1][2] and later adopted for navigation by the Song Dynasty Chinese during the 11th century.[3][4][5] The first usage of a compass recorded in Western Europe and the Islamic world occurred around 1190.[6][7]

Kompas Sofia
A simple dry magnetic portable compass
Smartphone Compass
A smartphone that can be used as a compass because of the magnetometer inside.

Magnetic compass

Military Compass of J. Lindsay Brough
A military compass that was used during World War I

The magnetic compass is the most familiar compass type. It functions as a pointer to "magnetic north", the local magnetic meridian, because the magnetized needle at its heart aligns itself with the horizontal component of the Earth's magnetic field. The magnetic field exerts a torque on the needle, pulling the North end or pole of the needle approximately toward the Earth's North magnetic pole, and pulling the other toward the Earth's South magnetic pole.[8] The needle is mounted on a low-friction pivot point, in better compasses a jewel bearing, so it can turn easily. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, it settles into its equilibrium orientation.

In navigation, directions on maps are usually expressed with reference to geographical or true north, the direction toward the Geographical North Pole, the rotation axis of the Earth. Depending on where the compass is located on the surface of the Earth the angle between true north and magnetic north, called magnetic declination can vary widely with geographic location. The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north. The locations of the Earth's magnetic poles slowly change with time, which is referred to as geomagnetic secular variation. The effect of this means a map with the latest declination information should be used.[9] Some magnetic compasses include means to manually compensate for the magnetic declination, so that the compass shows true directions.

Non-magnetic compasses

There are other ways to find north than the use of magnetism, and from a navigational point of view a total of seven possible ways exist[10] (where magnetism is one of the seven). Two sensors that utilize two of the remaining six principles are often also called compasses, i.e. the gyrocompass and GPS-compass.

Gyrocompass

A gyrocompass is similar to a gyroscope. It is a non-magnetic compass that finds true north by using an (electrically powered) fast-spinning wheel and friction forces in order to exploit the rotation of the Earth. Gyrocompasses are widely used on ships. They have two main advantages over magnetic compasses:

  • they find true north, i.e., the direction of Earth's rotational axis, as opposed to magnetic north,
  • they are not affected by ferromagnetic metal (including iron, steel, cobalt, nickel, and various alloys) in a ship's hull. (No compass is affected by nonferromagnetic metal, although a magnetic compass will be affected by any kind of wires with electric current passing through them.)

Large ships typically rely on a gyrocompass, using the magnetic compass only as a backup. Increasingly, electronic fluxgate compasses are used on smaller vessels. However, magnetic compasses are still widely in use as they can be small, use simple reliable technology, are comparatively cheap, are often easier to use than GPS, require no energy supply, and unlike GPS, are not affected by objects, e.g. trees, that can block the reception of electronic signals.

GPS receivers used as compasses

GPS receivers using two or more antennae mounted separately and blending the data with an inertial motion unit (IMU) can now achieve 0.02° in heading accuracy and have startup times in seconds rather than hours for gyrocompass systems. The devices accurately determine the positions (latitudes, longitudes and altitude) of the antennae on the Earth, from which the cardinal directions can be calculated. Manufactured primarily for maritime and aviation applications, they can also detect pitch and roll of ships. Small, portable GPS receivers with only a single antenna can also determine directions if they are being moved, even if only at walking pace. By accurately determining its position on the Earth at times a few seconds apart, the device can calculate its speed and the true bearing (relative to true north) of its direction of motion. Frequently, it is preferable to measure the direction in which a vehicle is actually moving, rather than its heading, i.e. the direction in which its nose is pointing. These directions may be different if there is a crosswind or tidal current.

GPS compasses share the main advantages of gyrocompasses. They determine true North,[10] as opposed to magnetic North, and they are unaffected by perturbations of the Earth's magnetic field. Additionally, compared with gyrocompasses, they are much cheaper, they work better in polar regions, they are less prone to be affected by mechanical vibration, and they can be initialized far more quickly. However, they depend on the functioning of, and communication with, the GPS satellites, which might be disrupted by an electronic attack or by the effects of a severe solar storm. Gyrocompasses remain in use for military purposes (especially in submarines, where magnetic and GPS compasses are useless), but have been largely superseded by GPS compasses, with magnetic backups, in civilian contexts.

History

The first compasses in ancient Han dynasty China were made of lodestone, a naturally magnetized ore of iron.[2][11] The compass was later used for navigation during the Song Dynasty of the 11th century.[12] Later compasses were made of iron needles, magnetized by striking them with a lodestone. Dry compasses began to appear around 1300 in Medieval Europe and the Islamic world.[13][7] This was supplanted in the early 20th century by the liquid-filled magnetic compass.[14]

Modern compasses

Walkers compass arp
A liquid-filled protractor or orienteering compass with lanyard

Magnetic compass

Modern compasses usually use a magnetized needle or dial inside a capsule completely filled with a liquid (lamp oil, mineral oil, white spirits, purified kerosene, or ethyl alcohol are common). While older designs commonly incorporated a flexible rubber diaphragm or airspace inside the capsule to allow for volume changes caused by temperature or altitude, some modern liquid compasses utilize smaller housings and/or flexible capsule materials to accomplish the same result.[15] The liquid inside the capsule serves to damp the movement of the needle, reducing oscillation time and increasing stability. Key points on the compass, including the north end of the needle are often marked with phosphorescent, photoluminescent, or self-luminous materials[16] to enable the compass to be read at night or in poor light. As the compass fill liquid is noncompressible under pressure, many ordinary liquid-filled compasses will operate accurately underwater to considerable depths.

Many modern compasses incorporate a baseplate and protractor tool, and are referred to variously as "orienteering", "baseplate", "map compass" or "protractor" designs. This type of compass uses a separate magnetized needle inside a rotating capsule, an orienting "box" or gate for aligning the needle with magnetic north, a transparent base containing map orienting lines, and a bezel (outer dial) marked in degrees or other units of angular measurement.[17] The capsule is mounted in a transparent baseplate containing a direction-of-travel (DOT) indicator for use in taking bearings directly from a map.[17]

Cammenga-lensatic-compass-model-27
Cammenga air filled lensatic compass

Other features found on modern orienteering compasses are map and romer scales for measuring distances and plotting positions on maps, luminous markings on the face or bezels, various sighting mechanisms (mirror, prism, etc.) for taking bearings of distant objects with greater precision, gimbal-mounted, "global" needles for use in differing hemispheres, special rare-earth magnets to stabilize compass needles, adjustable declination for obtaining instant true bearings without resorting to arithmetic, and devices such as inclinometers for measuring gradients.[18] The sport of orienteering has also resulted in the development of models with extremely fast-settling and stable needles utilizing rare-earth magnets for optimal use with a topographic map, a land navigation technique known as terrain association.[19]

The military forces of a few nations, notably the United States Army, continue to issue field compasses with magnetized compass dials or cards instead of needles. A magnetic card compass is usually equipped with an optical, lensatic, or prismatic sight, which allows the user to read the bearing or azimuth off the compass card while simultaneously aligning the compass with the objective (see photo). Magnetic card compass designs normally require a separate protractor tool in order to take bearings directly from a map.[20][21]

The U.S. M-1950 military lensatic compass does not use a liquid-filled capsule as a damping mechanism, but rather electromagnetic induction to control oscillation of its magnetized card. A "deep-well" design is used to allow the compass to be used globally with a card tilt of up to 8 degrees without impairing accuracy.[22] As induction forces provide less damping than fluid-filled designs, a needle lock is fitted to the compass to reduce wear, operated by the folding action of the rear sight/lens holder. The use of air-filled induction compasses has declined over the years, as they may become inoperative or inaccurate in freezing temperatures or extremely humid environments due to condensation or water ingress.[23]

Some military compasses, like the U.S. M-1950 (Cammenga 3H) military lensatic compass, the Silva 4b Militaire, and the Suunto M-5N(T) contain the radioactive material tritium (3
1
H
) and a combination of phosphors.[24] The U.S. M-1950 equipped with self-luminous lighting contains 120 mCi (millicuries) of tritium. The purpose of the tritium and phosphors is to provide illumination for the compass, via radioluminescent tritium illumination, which does not require the compass to be "recharged" by sunlight or artificial light.[25] However, tritium has a half-life of only about 12 years,[26] so a compass that contains 120 mCi of tritium when new will contain only 60 when it is 12 years old, 30 when it is 24 years old, and so on. Consequently, the illumination of the display will fade.

Mariners' compasses can have two or more magnets permanently attached to a compass card, which moves freely on a pivot. A lubber line, which can be a marking on the compass bowl or a small fixed needle, indicates the ship's 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.

Thumb compass

Compasses orienteering
Thumb compass on left

A thumb compass is a type of compass commonly used in orienteering, a sport in which map reading and terrain association are paramount. Consequently, most thumb compasses have minimal or no degree markings at all, and are normally used only to orient the map to magnetic north. An oversized rectangular needle or north indicator aids visibility. Thumb compasses are also often transparent so that an orienteer can hold a map in the hand with the compass and see the map through the compass. The best models use rare-earth magnets to reduce needle settling time to 1 second or less.

Solid state compasses

Motorola Xoom - AKM Semiconductor AKM8975-1693
3-axis electronic magnetometer AKM8975 by AKM Semiconductor

Small compasses found in clocks, mobile phones, and other electronic devices are solid-state microelectromechanical systems (MEMS) compasses, usually built out of two or three magnetic field sensors that provide data for a microprocessor. 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 either used internally, or sent to a display unit. The sensor uses highly calibrated internal electronics to measure the response of the device to the Earth's magnetic field.

Specialty compasses

Brunton
A standard Brunton Geo, used commonly by geologists

Apart from navigational compasses, other specialty compasses have also been designed to accommodate specific uses. These include:

  • Qibla compass, which is used by Muslims to show the direction to Mecca for prayers.
  • Optical or prismatic hand-bearing compass, most often used by surveyors, but also by cave explorers, foresters, and geologists. These compasses generally use a liquid-damped capsule[27] and magnetized floating compass dial with an integral optical sight, often fitted with built-in photoluminescent or battery-powered illumination.[28] Using the optical sight, such compasses can be read with extreme accuracy when taking bearings to an object, often to fractions of a degree. Most of these compasses are designed for heavy-duty use, with high-quality needles and jeweled bearings, and many are fitted for tripod mounting for additional accuracy.[28]
  • Trough compasses, mounted in a rectangular box whose length was often several times its width, date back several centuries. They were used for land surveying, particularly with plane tables.

Limitations of the magnetic compass

מצפן
A close up photo of a geological compass

The magnetic compass is very reliable at moderate latitudes, but in geographic regions near the Earth's magnetic poles it becomes unusable. As the compass is moved closer to one of the magnetic poles, the magnetic declination, the difference between the direction to geographical north and magnetic north, becomes greater and greater. At some point close to the magnetic pole the compass will not indicate any particular direction but will begin to drift. Also, the needle starts to point up or down when getting closer to the poles, because of the so-called magnetic inclination. Cheap compasses with bad bearings may get stuck because of this and therefore indicate a wrong direction.

Magnetic compasses are influenced by any fields other than Earth's. Local environments may contain magnetic mineral deposits and artificial sources such as MRIs, large iron or steel bodies, electrical engines or strong permanent magnets. Any electrically conductive body produces its own magnetic field when it is carrying an electric current. Magnetic compasses are prone to errors in the neighborhood of such bodies. Some compasses include magnets which can be adjusted to compensate for external magnetic fields, making the compass more reliable and accurate.

A compass is also subject to errors when the compass is accelerated or decelerated in an airplane or automobile. Depending on which of the Earth's hemispheres the compass is located and if the force is acceleration or deceleration the compass will increase or decrease the indicated heading. Compasses that include compensating magnets are especially prone to these errors, since accelerations tilt the needle, bringing it closer or further from the magnets.

Another error of the mechanical compass is turning error. When one turns from a heading of east or west the compass will lag behind the turn or lead ahead of the turn. Magnetometers, and substitutes such as gyrocompasses, are more stable in such situations.

Construction of a magnetic compass

Magnetic needle

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. For example, a magnetised rod can be created by repeatedly rubbing an iron rod with a magnetic lodestone. 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.

Needle-and-bowl device

If a needle is rubbed on a lodestone or other magnet, the needle becomes magnetized. When it is inserted in a cork or piece of wood, and placed in a bowl of water it becomes a compass. Such devices were universally used as compass until the invention of the box-like compass with a 'dry' pivoting needle sometime around 1300.

Points of the compass

Boussole fantassin russe
Wrist compass of the Soviet Army with counterclockwise double graduation: 60° (like a watch) and 360°

Originally, many compasses were marked only as to the direction of magnetic north, or to the four cardinal points (north, south, east, west). Later, these were divided, in China into 24, and in Europe into 32 equally spaced points around the compass card. For a table of the thirty-two points, see compass points.

In the modern era, the 360-degree system took hold. This system is still in use today for civilian navigators. The degree system spaces 360 equidistant points located clockwise around the compass dial. In the 19th century some European nations adopted the "grad" (also called grade or gon) system instead, where a right angle is 100 grads to give a circle of 400 grads. Dividing grads into tenths to give a circle of 4000 decigrades has also been used in armies.

Most military forces have adopted the French "millieme" system. This is an approximation of a milli-radian (6283 per circle), in which the compass dial is spaced into 6400 units or "mils" for additional precision when measuring angles, laying artillery, etc. The value to the military is that one angular mil subtends approximately one metre at a distance of one kilometer. Imperial Russia used a system derived by dividing the circumference of a circle into chords of the same length as the radius. Each of these was divided into 100 spaces, giving a circle of 600. The Soviet Union divided these into tenths to give a circle of 6000 units, usually translated as "mils". This system was adopted by the former Warsaw Pact countries (e.g. Soviet Union, East Germany), often counterclockwise (see picture of wrist compass). This is still in use in Russia.

Compass balancing (magnetic dip)

Because the Earth's magnetic field's inclination and intensity vary at different latitudes, compasses are often balanced during manufacture so that the dial or needle will be level, eliminating needle drag which can give inaccurate readings. 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 individual zone balancing prevents excessive dipping of one end of the needle which can cause the compass card to stick and give false readings.[29]

Some compasses feature a special needle balancing system that will accurately indicate magnetic north regardless of the particular magnetic zone. Other magnetic compasses have a small sliding counterweight installed on the needle itself. This sliding counterweight, called a 'rider', can be used for counterbalancing the needle against the dip caused by inclination if the compass is taken to a zone with a higher or lower dip.[29]

Compass correction

MuseeMarine-compas-p1000468
A binnacle containing a ship's standard compass, with the two iron balls which correct the effects of ferromagnetic materials. This unit is on display in a museum.

Like any magnetic device, compasses are affected by nearby ferrous materials, as well as by strong local electromagnetic forces. Compasses used for wilderness land navigation should not be used in proximity to ferrous metal objects or electromagnetic fields (car electrical systems, automobile engines, steel pitons, etc.) as that can affect their accuracy.[30] Compasses are particularly difficult to use accurately in or near trucks, cars or other mechanized vehicles even when corrected for deviation by the use of built-in magnets or other devices. Large amounts of ferrous metal combined with the on-and-off electrical fields caused by the vehicle's ignition and charging systems generally result in significant compass errors.

At sea, a ship's compass must also be corrected for errors, called 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 ferromagnetic materials in the compass's environment can be corrected by two iron balls mounted on either side of the compass binnacle in concert with permanent magnets and a Flinders bar.[31] The coefficient represents the error in the lubber line, while the ferromagnetic effects and the non-ferromagnetic component.[32]

A similar process is used to calibrate the compass in light general aviation aircraft, with the compass deviation card often mounted permanently just above or below the magnetic compass on the instrument panel. Fluxgate electronic compasses can be calibrated automatically, and can also be programmed with the correct local compass variation so as to indicate the true heading.

Using a magnetic compass

CompassUseMapMarked
Turning the compass scale on the map (D – the local magnetic declination)
CompassUseTargetMarked
When the needle is aligned with and superimposed over the outlined orienting arrow on the bottom of the capsule, the degree figure on the compass ring at the direction-of-travel (DOT) indicator gives the magnetic bearing to the target (mountain).

A magnetic compass points to magnetic north pole, which is approximately 1,000 miles from the true geographic North Pole. A magnetic compass's user can determine true North by finding the magnetic north and then correcting for variation and deviation. Variation is defined as the angle between the direction of true (geographic) north and the direction of the meridian between the magnetic poles. Variation values for most of the oceans had been calculated and published by 1914.[33] Deviation refers to the response of the compass to local magnetic fields caused by the presence of iron and electric currents; one can partly compensate for these by careful location of the compass and the placement of compensating magnets under the compass itself. Mariners have long known that these measures do not completely cancel deviation; hence, they performed an additional step by measuring the compass bearing of a landmark with a known magnetic bearing. They then pointed their ship to the next compass point and measured again, graphing their results. In this way, correction tables could be created, which would be consulted when compasses were used when traveling in those locations.

Mariners are concerned about very accurate measurements; however, casual users need not be concerned with differences between magnetic and true North. Except in areas of extreme magnetic declination variance (20 degrees or more), this is enough to protect from walking in a substantially different direction than expected over short distances, provided the terrain is fairly flat and visibility is not impaired. By carefully recording distances (time or paces) and magnetic bearings traveled, one can plot a course and return to one's starting point using the compass alone.[34]

Measuring azimuth with a compass
Soldier using a prismatic compass to get an azimuth

Compass navigation in conjunction with a map (terrain association) requires a different method. To take a map bearing or true bearing (a bearing taken in reference to true, not magnetic north) to a destination with a protractor compass, the edge of the compass is placed on the map so that it connects the current location with the desired destination (some sources recommend physically drawing a line). The orienting lines in the base of the compass dial are then rotated to align with actual or true north by aligning them with a marked line of longitude (or the vertical margin of the map), ignoring the compass needle entirely.[35] The resulting true bearing or map bearing may then be read at the degree indicator or direction-of-travel (DOT) line, which may be followed as an azimuth (course) to the destination. If a magnetic north bearing or compass bearing is desired, the compass must be adjusted by the amount of magnetic declination before using the bearing so that both map and compass are in agreement.[35] In the given example, the large mountain in the second photo was selected as the target destination on the map. Some compasses allow the scale to be adjusted to compensate for the local magnetic declination; if adjusted correctly, the compass will give the true bearing instead of the magnetic bearing.

The modern hand-held protractor compass always has an additional direction-of-travel (DOT) arrow or indicator inscribed on the baseplate. To check one's progress along a course or azimuth, or to ensure that the object in view is indeed the destination, a new compass reading may be taken to the target if visible (here, the large mountain). After pointing the DOT arrow on the baseplate at the target, the compass is oriented so that the needle is superimposed over the orienting arrow in the capsule. The resulting bearing indicated is the magnetic bearing to the target. Again, if one is using "true" or map bearings, and the compass does not have preset, pre-adjusted declination, one must additionally add or subtract magnetic declination to convert the magnetic bearing into a true bearing. The exact value of the magnetic declination is place-dependent and varies over time, though declination is frequently given on the map itself or obtainable on-line from various sites. If the hiker has been following the correct path, the compass' corrected (true) indicated bearing should closely correspond to the true bearing previously obtained from the map.

A compass should be laid down on a level surface so that the needle only rests or hangs on the bearing fused to the compass casing – if used at a tilt, the needle might touch the casing on the compass and not move freely, hence not pointing to the magnetic north accurately, giving a faulty reading. To see if the needle is well leveled, look closely at the needle, and tilt it slightly to see if the needle is swaying side to side freely and the needle is not contacting the casing of the compass. If the needle tilts to one direction, tilt the compass slightly and gently to the opposing direction until the compass needle is horizontal, lengthwise. Items to avoid around compasses are magnets of any kind and any electronics. Magnetic fields from electronics can easily disrupt the needle, preventing it from aligning with the Earth's magnetic fields, causing inaccurate readings. The Earth's natural magnetic forces are considerably weak, measuring at 0.5 gauss and magnetic fields from household electronics can easily exceed it, overpowering the compass needle. Exposure to strong magnets, or magnetic interference can sometimes cause the magnetic poles of the compass needle to differ or even reverse. Avoid iron rich deposits when using a compass, for example, certain rocks which contain magnetic minerals, like Magnetite. This is often indicated by a rock with a surface which is dark and has a metallic luster, not all magnetic mineral bearing rocks have this indication. To see if a rock or an area is causing interference on a compass, get out of the area, and see if the needle on the compass moves. If it does, it means that the area or rock the compass was previously at is causing interference and should be avoided.

See also

Notes

  1. ^ Li Shu-hua, p. 176
  2. ^ a b Lowrie, William (2007). Fundamentals of Geophysics. London: Cambridge University Press. p. 281. ISBN 978-0-521-67596-3. Early in the Han Dynasty, between 300–200 BC, the Chinese fashioned a rudimentary compass out of lodestone ... the compass may have been used in the search for gems and the selection of sites for houses ... their directive power led to the use of compasses for navigation
  3. ^ Kreutz, p. 367
  4. ^ Needham, p. 252
  5. ^ Li Shu-hua, p. 182f.
  6. ^ Kreutz, p. 370
  7. ^ a b Schmidl, Petra G. (2014-05-08). "Compass". In Ibrahim Kalin (ed.). The Oxford Encyclopedia of Philosophy, Science, and Technology in Islam. Oxford University Press. pp. 144–146. ISBN 978-0-19-981257-8.
  8. ^ The magnetic lines of force in the Earth's field do not accurately follow great circles around the planet, passing exactly over the magnetic poles. Therefore the needle of a compass only approximately points to the magnetic poles.
  9. ^ "Declination Adjustment on a Compass". Rei.com. Retrieved 2015-06-06.
  10. ^ a b Gade, Kenneth (2016). "The Seven Ways to Find Heading" (PDF). The Journal of Navigation. 69 (5): 955–970. doi:10.1017/S0373463316000096.
  11. ^ Guarnieri, M. (2014). "Once Upon a Time, the Compass". IEEE Industrial Electronics Magazine. 8 (2): 60–63. doi:10.1109/MIE.2014.2316044.
  12. ^ Merrill, Ronald T.; McElhinny, Michael W. (1983). The Earth's magnetic field: Its history, origin and planetary perspective (2nd printing ed.). San Francisco: Academic press. p. 1. ISBN 978-0-12-491242-7.
  13. ^ Lane, p. 615
  14. ^ W.H. Creak: "The History of the Liquid Compass", The Geographical Journal, Vol. 56, No. 3 (1920), pp. 238–239
  15. ^ Gear Review: Kasper & Richter Alpin Compass, OceanMountainSky.Com
  16. ^ Nemoto & Co. Ltd., Article Archived 2008-12-05 at the Wayback Machine: In addition to ordinary phosphorescent luminous paint (zinc sulfide), brighter photoluminescent coatings which include radioactive isotopes such as Strontium-90, usually in the form of strontium aluminate, or tritium, which is a radioactive isotope of hydrogen are now being used on modern compasses. Tritium has the advantage that its radiation has such low energy that it cannot penetrate a compass housing.
  17. ^ a b Johnson, G. Mark (2003-03-26). The Ultimate Desert Handbook. McGraw-Hill Professional. p. 110. ISBN 978-0-07-139303-4.
  18. ^ Johnson, G. Mark (2003-03-26). The Ultimate Desert Handbook. McGraw-Hill Professional. pp. 110–111. ISBN 978-0-07-139303-4.
  19. ^ Kjernsmo, Kjetil, [www.learn-orienteering.org/old/buying.html How to use a Compass], retrieved 8 April 2012
  20. ^ Johnson, G. Mark (2003-03-26). The Ultimate Desert Handbook. McGraw-Hill Professional. p. 112. ISBN 978-0-07-139303-4.
  21. ^ U.S. Army, Map Reading and Land Navigation, FM 21-26, Headquarters, Dept. of the Army, Washington, D.C. (7 May 1993), ch. 11, pp. 1-3: Any 'floating card' type compass with a straightedge or centerline axis can be used to read a map bearing by orienting the map to magnetic north using a drawn magnetic azimuth, but the process is far simpler with a protractor compass.
  22. ^ Article MIL-PRF-10436N, rev. 31 October 2003, Washington, D.C.: U.S. Dept. of Defense
  23. ^ Kearny, Cresson H., Jungle Snafus ... And Remedies, Oregon Institute Press (1996), ISBN 1-884067-10-7, pp. 164–170: In 1989, one U.S. Army jungle infantry instructor reported that about 20% of the issue lensatic compasses in his company used in a single jungle exercise in Panama were ruined within three weeks by rain and humidity.
  24. ^ Ministry of Defence, Manual of Map Reading and Land Navigation, HMSO Army Code 70947 (1988), ISBN 0-11-772611-7, 978-0-11-772611-6, ch. 8, sec. 26, pp. 6–7; ch. 12, sec. 39, p. 4
  25. ^ "Military Compass". Orau.org. Retrieved 2009-06-30.
  26. ^ CRC Handbook of Chemistry and Physics. p. B247
  27. ^ Kramer, Melvin G., U.S. Patent No. 4175333, Magnetic Compass, Riverton, Wyoming: The Brunton Company, pub. 27 November 1979: The Brunton Pocket Transit, which uses magnetic induction damping, is an exception.
  28. ^ a b Johnson, G. Mark (2003-03-26). The Ultimate Desert Handbook. McGraw-Hill Professional. pp. 113–114. ISBN 978-0-07-139303-4.
  29. ^ a b Global compasses, MapWorld.
  30. ^ Johnson, G. Mark (2003-03-26). The Ultimate Desert Handbook. McGraw-Hill Professional. p. 122. ISBN 978-0-07-139303-4.
  31. ^ GEOSPATIAL-INTELLIGENCE AGENCY, National (2004). "Handbook of Magnetic Compass Adjustment" (PDF).
  32. ^ Lushnikov, E. (December 2015). "Magnetic Compass in Modern Maritime Navigation". TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation. 9 (4): 539–543. doi:10.12716/1001.09.04.10. ISSN 2083-6481. Retrieved 11 February 2016.
  33. ^ Wright, Monte, Most Probable Position, University Press of Kansas, Lawrence, 1972, p.7
  34. ^ Johnson, G. Mark (2003-03-26). The Ultimate Desert Handbook. McGraw-Hill Professional. p. 149. ISBN 978-0-07-139303-4.
  35. ^ a b Johnson, G. Mark (2003-03-26). The Ultimate Desert Handbook. McGraw-Hill Professional. pp. 134–135. ISBN 978-0-07-139303-4.

References

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  • Gubbins, David, Encyclopedia of Geomagnetism and Paleomagnetism, Springer Press (2007), ISBN 1-4020-3992-1, 978-1-4020-3992-8
  • Gurney, Alan (2004) Compass: A Story of Exploration and Innovation, London : Norton, ISBN 0-393-32713-2
  • Johnson, G. Mark, The Ultimate Desert Handbook, 1st Ed., Camden, Maine: McGraw-Hill (2003), ISBN 0-07-139303-X
  • King, David A. (1983). "The Astronomy of the Mamluks". Isis. 74 (4): 531–555. doi:10.1086/353360.
  • Kreutz, Barbara M. (1973) "Mediterranean Contributions to the Medieval Mariner's Compass", Technology and Culture, 14 (3: July), pp. 367–383 JSTOR 3102323
  • Lane, Frederic C. (1963) "The Economic Meaning of the Invention of the Compass", The American Historical Review, 68 (3: April), pp. 605–617 JSTOR 1847032
  • Li Shu-hua (1954) "Origine de la Boussole 11. Aimant et Boussole", Isis, 45 (2: July), pp. 175–196
  • Ludwig, Karl-Heinz and Schmidtchen, Volker (1997) Metalle und Macht: 1000 bis 1600, Propyläen Technikgeschichte, Berlin: Propyläen Verlag, ISBN 3-549-05633-8
  • Ma, Huan (1997) Ying-yai sheng-lan [The overall survey of the ocean's shores (1433)], Feng, Ch'eng-chün (ed.) and Mills, J.V.G. (transl.), Bangkok : White Lotus Press, ISBN 974-8496-78-3
  • Needham, Joseph (1986) Science and civilisation in China, Vol. 4: "Physics and physical technology", Pt. 1: "Physics", Taipei: Caves Books, originally publ. by Cambridge University Press (1962), ISBN 0-521-05802-3
  • Needham, Joseph and Ronan, Colin A. (1986) The shorter Science and civilisation in China : an abridgement of Joseph Needham's original text, Vol. 3, Chapter 1: "Magnetism and Electricity", Cambridge University Press, ISBN 0-521-25272-5
  • Seidman, David, and Cleveland, Paul, The Essential Wilderness Navigator, Ragged Mountain Press (2001), ISBN 0-07-136110-3
  • Taylor, E.G.R. (1951). "The South-Pointing Needle". Imago Mundi. 8: 1–7. doi:10.1080/03085695108591973.
  • Williams, J.E.D. (1992) From Sails to Satellites: the origin and development of navigational science, Oxford University Press, ISBN 0-19-856387-6
  • Wright, Monte Duane (1972) Most Probable Position: A History of Aerial Navigation to 1941, The University Press of Kansas, LCCN 72-79318
  • Zhou, Daguan (2007) The customs of Cambodia, translated into English from the French version by Paul Pelliot of Zhou's Chinese original by J. Gilman d'Arcy Paul, Phnom Penh : Indochina Books, prev publ. by Bangkok : Siam Society (1993), ISBN 974-8298-25-6

External links

BBVA Stadium

BBVA Stadium (formerly BBVA Compass Stadium) is an American multi-purpose stadium located in Houston, Texas that is home to the Houston Dynamo, a Major League Soccer club, the Houston Dash of the National Women's Soccer League, and to Texas Southern Tigers football. The stadium is the result of combined commitments of $35.5 million from the city of Houston and $60 million from the Houston Dynamo. Harris County agreed to pay for half of the land in exchange for the ability to jointly own the stadium after its completion date in May 2012. BBVA, Banco Bilbao Vizcaya Argentaria, is the stadium's sponsor company.

The stadium is located on a tract of land bordered by Texas, Walker, Emancipation, and Hutchins in East Downtown and east of Interstate 69/U.S. Route 59 and Downtown Houston.

BeiDou

The BeiDou Navigation Satellite System (BDS) (Chinese: 北斗卫星导航系统; pinyin: Běidǒu Wèixīng Dǎoháng Xìtǒng [pèitòu wêiɕíŋ tàuxǎŋ ɕîtʰʊ̀ŋ]) is a Chinese satellite navigation system. It consists of two separate satellite constellations. The first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites which since 2000 has offered limited coverage and navigation services, mainly for users in China and neighboring regions. Beidou-1 was decommissioned at the end of 2012.

The second generation of the system, officially called the BeiDou Navigation Satellite System (BDS) and also known as COMPASS or BeiDou-2, became operational in China in December 2011 with a partial constellation of 10 satellites in orbit. Since December 2012, it has been offering services to customers in the Asia-Pacific region.In 2015, China started the build-up of the third generation BeiDou system (BeiDou-3) for global coverage constellation. The first BDS-3 satellite was launched on 30 March 2015. As of October 2018, fifteen BDS-3 satellites have been launched. BeiDou-3 will eventually consist of 35 satellites and is expected to provide global services upon completion in 2020. When fully completed, BeiDou will provide an alternative global navigation satellite system to the United States owned Global Positioning System (GPS), the Russian GLONASS or European Galileo systems and is expected to be more accurate than these. It was claimed in 2016 that BeiDou-3 will reach millimeter-level accuracy (with post-processing).According to China Daily, in 2015, fifteen years after the satellite system was launched, it was generating a turnover of $31.5 billion per annum for major companies such as China Aerospace Science and Industry Corp, AutoNavi Holdings Ltd, and China North Industries Group Corp.On 27 December 2018, BeiDou Navigation Satellite System started to provide global services.

Bridge (nautical)

The bridge of a ship is the room or platform from which the ship can be commanded. When a ship is under way, the bridge is manned by an officer of the watch aided usually by an able seaman acting as lookout. During critical maneuvers the captain will be on the bridge, often supported by an officer of the watch, an able seaman on the wheel and sometimes a pilot, if required.

Cardinal direction

The four cardinal directions, or cardinal points, are the directions north, east, south, and west, commonly denoted by their initials N, E, S, and W. East and west are perpendicular (at right angles) to north and south, with east being in the clockwise direction of rotation from north and west being directly opposite east. Points between the cardinal directions form the points of the compass.

The intercardinal (also called the intermediate directions and, historically, ordinal) directions are northeast (NE), southeast (SE), southwest (SW), and northwest (NW). 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 that is shown to the right (e.g. NNE, ENE, and ESE).

Compass (drawing tool)

A pair of compasses, also known as a compass, is a technical drawing instrument that can be used for inscribing circles or arcs. As dividers, they can also be used as tools to measure distances, in particular on maps. Compasses can be used for mathematics, drafting, navigation and other purposes.

Compasses are usually made of metal or plastic, and consist of two parts connected by a hinge which can be adjusted to allow the changing of the radius of the circle drawn. Typically one part has a spike at its end, and the other part a pencil, or sometimes a pen.

Prior to computerization, compasses and other tools for manual drafting were often packaged as a "bow set" with interchangeable parts. By the mid-twentieth century, circle templates supplemented the use of compasses. Today these facilities are more often provided by computer-aided design programs, so the physical tools serve mainly a didactic purpose in teaching geometry, technical drawing, etc.

Compass Airlines (North America)

Compass Airlines, LLC, is a regional airline headquartered in Delta Air Lines Building C at Minneapolis−Saint Paul International Airport in Fort Snelling, Hennepin County, Minnesota; prior to December 16, 2009, it was headquartered in unincorporated Fairfax County, Virginia, United States, east of the Chantilly CDP. The airline launched inaugural service with a single Bombardier CRJ200LR aircraft under the Northwest Airlink (now Delta Connection) brand between Minneapolis/St. Paul and Washington, D.C. on May 2, 2007. On August 21, 2007, it began flying two Embraer 175 76-passenger aircraft, and expanded to 36 aircraft by December 2008.

In July 2010, the airline was purchased from Delta Air Lines and became a wholly owned subsidiary of Trans States Holdings. This airline is the only remaining airline of the former Northwest Group.

Compass Group

Compass Group plc is a British multinational contract foodservice company headquartered in Chertsey, Surrey. It is the largest contract foodservice company in the world. Compass Group has operations in about 50 countries and employs over 550,000 people. It serves around 5.5 billion meals a year in locations including offices and factories, schools, universities, hospitals, major sports and cultural venues, mining camps, correctional facilities and offshore oil platforms. Compass Group is listed on the London Stock Exchange and is a constituent of the FTSE 100 Index. It is also a Fortune Global 500 company.

Compass Media Networks

Compass Media Networks is an American radio network. The company launched in January 2009.

It is owned by former Westwood One CEO and former COO of Connoisseur Media, Peter Kosann. The company focuses on radio and offers representation and marketing services for national radio.

Compass rose

A compass rose, sometimes called a windrose or Rose of the Winds, is a figure on a compass, map, nautical chart, or monument used to display the orientation of the cardinal directions (north, east, south, and west) and their intermediate points. It is also the term for the graduated markings found on the traditional magnetic compass. Today, the idea of a compass rose is found on, or featured in, almost all navigation systems, including nautical charts, non-directional beacons (NDB), VHF omnidirectional range (VOR) systems, global-positioning systems (GPS), and similar equipment.

The modern compass rose has eight principal winds. Listed clockwise, these are:

Although modern compasses use the names of the eight principal directions (N, NE, E, SE, etc.), older compasses use the traditional Italianate wind names of Medieval origin (Tramontana, Greco, Levante, etc.)

4-point compass roses use only the four "basic winds" or "cardinal directions" (North, East, South, West), with angles of difference at 90°.

8-point compass roses use the eight principal winds—that is, the four cardinal directions (N, E, S, W) plus the four "intercardinal" or "ordinal directions" (NE, SE, SW, NW), at angles of difference of 45°.

16-point compass roses are constructed by bisecting the angles of the principal winds to come up with intermediate compass points, known as half-winds, at angles of difference of 22​1⁄2°. The names of the half-winds are simply combinations of the principal winds to either side, principal then ordinal. E.g. North-northeast (NNE), East-northeast (ENE), etc.

32-point compass roses are constructed by bisecting these angles, and coming up with quarter-winds at 11​1⁄4° angles of difference. Quarter-wind names are constructed with the names "X by Y", which can be read as "one quarter wind from X toward Y", where X is one of the eight principal winds and Y is one of the two adjacent cardinal directions. For example, North-by-east (NbE) is one quarter wind from North towards East, Northeast-by-north (NEbN) is one quarter wind from Northeast toward North. Naming all 32 points on the rose is called "boxing the compass".

The 32-point rose has the uncomfortable number of 11​1⁄4° between points, but is easily found by halving divisions and may have been easier for those not using a 360° circle. Using gradians, of which there are 400 in a circle, the sixteen-point rose will have twenty-five gradians per point.

Compass saw

A compass saw is a type of saw used for making curved cuts known as compasses, particularly in confined spaces where a larger saw would not fit.

East

East is one of the four cardinal directions or points of the compass. It is the opposite direction from west.

Geography and cartography in medieval Islam

Medieval Islamic geography was based on Hellenistic geography and reached its apex with Muhammad al-Idrisi in the 11th century.

Magnetic declination

Magnetic declination, or magnetic variation, is the angle on the horizontal plane between magnetic north (the direction the north end of a magnetized compass needle points, corresponding to the direction of the Earth's magnetic field lines) and true north (the direction along a meridian towards the geographic North Pole). This angle varies depending on position on the Earth's surface and changes over time.

Somewhat more formally, Bowditch defines variation as “the angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north. The angle between magnetic and grid meridians is called grid magnetic angle, grid variation, or grivation.”By convention, declination is positive when magnetic north is east of true north, and negative when it is to the west. Isogonic lines are lines on the Earth's surface along which the declination has the same constant value, and lines along which the declination is zero are called agonic lines. The lowercase Greek letter δ (delta) is frequently used as the symbol for magnetic declination.

The term magnetic deviation is sometimes used loosely to mean the same as magnetic declination, but more correctly it refers to the error in a compass reading induced by nearby metallic objects, such as iron on board a ship or aircraft.

Magnetic declination should not be confused with magnetic inclination, also known as magnetic dip, which is the angle that the Earth's magnetic field lines make with the downward side of the horizontal plane.

Northern Lights (novel)

Northern Lights (known as The Golden Compass in North America and some other countries) is a young-adult fantasy novel by Philip Pullman, published by Scholastic UK in 1995. Set in a parallel universe, it features the journey of Lyra Belacqua to the Arctic in search of her missing friend, Roger Parslow, and her imprisoned uncle, Lord Asriel, who has been conducting experiments with a mysterious substance known as "Dust".

Northern Lights is the first book of a trilogy, His Dark Materials (1995 to 2000). Alfred A. Knopf published the first US edition April 1996, entitled The Golden Compass. Under that title it has been adapted as a 2007 feature film by Hollywood and as a companion video game.

Pullman won the 1995 Carnegie Medal from the Library Association, recognising the year's outstanding British children's book. For the 70th anniversary of the Medal, it was named one of the top ten winning works by a panel, composing the ballot for a public election of the all-time favourite. Northern Lights won the public vote from that shortlist and was thus named the all-time "Carnegie of Carnegies" on 21 June 2007.

Points of the compass

The points of the compass mark the divisions on a compass, which is primarily divided into the four cardinal directions: north, south, east, and west. These points are further subdivided by the addition of the four intercardinal (or ordinal) directions—northeast (NE), southeast (SE), southwest (SW), and northwest (NW)—to indicate the eight principal winds. In meteorological usage, further intermediate points between the cardinal and intercardinal directions, such as north-northeast (NNE) are added to give the sixteen points of a compass rose.

At the most complete division are the full thirty-two points of the mariner's compass, which adds points such as north by east (NbE; sometimes NxE) between north and north-northeast, and northeast by north (NEbN; NExN) between north-northeast and northeast. A compass point allows reference to a specific course (or azimuth) in a colloquial fashion, without having to compute or remember degrees.

The European nautical tradition retained the term "one point" to describe ​1⁄32 of a circle in such phrases as "two points to starboard". By the middle of the 18th century, the 32-point system was extended with half- and quarter-points to allow 128 directions to be differentiated.

Political spectrum

A political spectrum is a system to characterize and classify different political positions in relation to one another upon one or more geometric axes that represent independent political dimensions. The expressions political compass and political map are used to refer to the politcal spectrum as well, especially to popular two-dimensional models of it.Most long-standing spectra include the left–right dimension, which originally referred to seating arrangements in the French parliament after the Revolution (1789–1799), with radicals on the left and aristocrats on the right. While communism and socialism are usually regarded internationally as being on the left, conservatism and fascism are regarded internationally as being on the right. Liberalism can mean different things in different contexts: sometimes on the left (social liberalism), sometimes on the right (classical liberalism). Those with an intermediate outlook are sometimes classified as centrists. That said, liberals and neoliberals are often called centrists too. Politics that rejects the conventional left–right spectrum is often known as syncretic politics, though the label tends to mischaracterize positions that have a logical location on a two-axis spectrum because they seem randomly brought together on a one-axis left-right spectrum.

Political scientists have frequently noted that a single left–right axis is too simplistic and insufficient for describing the existing variation in political beliefs and included other axes. Though the descriptive words at polar opposites may vary, the axes of popular biaxial spectra are usually split between economic issues (on a left–right dimension) and socio-cultural issues (on a authority–liberty dimension).

Square and Compasses

The Square and Compasses (or, more correctly, a square and a set of compasses joined together) is the single most identifiable symbol of Freemasonry. Both the square and compasses are architect's tools and are used in Masonic ritual as emblems to teach symbolic lessons.

Some Lodges and rituals explain these symbols as lessons in conduct: for example, Duncan's Masonic Monitor of 1866 explains them as: "The square, to square our actions; The compasses, to circumscribe and keep us within bounds with all mankind". However, as Freemasonry is non-dogmatic, there is no general interpretation for these symbols (or any Masonic symbol) that is used by Freemasonry as a whole.

Straightedge and compass construction

Straightedge and compass construction, also known as ruler-and-compass construction or classical construction, is the construction of lengths, angles, and other geometric figures using only an idealized ruler and compass.

The idealized ruler, known as a straightedge, is assumed to be infinite in length, have only one edge, and no markings on it. The compass is assumed to "collapse" when lifted from the page, so may not be directly used to transfer distances. (This is an unimportant restriction since, using a multi-step procedure, a distance can be transferred even with collapsing compass; see compass equivalence theorem.) More formally, the only permissible constructions are those granted by Euclid's first three postulates.

It turns out to be the case that every point constructible using straightedge and compass may also be constructed using compass alone.

The ancient Greek mathematicians first conceived straightedge and compass constructions, and a number of ancient problems in plane geometry impose this restriction. The ancient Greeks developed many constructions, but in some cases were unable to do so. Gauss showed that some polygons are constructible but that most are not. Some of the most famous straightedge and compass problems were proven impossible by Pierre Wantzel in 1837, using the mathematical theory of fields.

In spite of existing proofs of impossibility, some persist in trying to solve these problems. Many of these problems are easily solvable provided that other geometric transformations are allowed: for example, doubling the cube is possible using geometric constructions, but not possible using straightedge and compass alone.

In terms of algebra, a length is constructible if and only if it represents a constructible number, and an angle is constructible if and only if its cosine is a constructible number. A number is constructible if and only if it can be written using the four basic arithmetic operations and the extraction of square roots but of no higher-order roots.

The Golden Compass (film)

The Golden Compass is a 2007 fantasy adventure film based on Northern Lights, the first novel in Philip Pullman's trilogy His Dark Materials. Written and directed by Chris Weitz, it stars Nicole Kidman, Dakota Blue Richards, Daniel Craig, Sam Elliott, Eva Green, and Ian McKellen. The project was announced in February 2002, but difficulties over the script and the selection of a director caused significant delays. At US$180 million, it was one of New Line Cinema's most expensive projects ever, and its disappointing results in the US contributed to New Line's February 2008 restructuring.The film depicts the adventures of Lyra Belacqua, an orphan living in a parallel universe where a dogmatic ruling power called the Magisterium opposes free inquiry. Children in that universe are being kidnapped by an unknown group called the Gobblers who are supported by the Magisterium. Lyra joins a tribe of sea-farers on a trip to the far North, the land of the armoured polar bears, in search of the missing children.

Before its release, the film received criticism from secularist organisations and fans of the His Dark Materials trilogy for the dilution of elements of the story which were critical of religion, as well as from some religious organisations for the source material's anti-religious themes. The studio ordered significant changes late in post-production, which Weitz later called a "terrible" experience. Although the film's visual effects (which Weitz has called the film's "most successful element") won both a BAFTA and an Academy Award, critical reception was mixed and revenue lower than anticipated.

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