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Navigating With Compasses in Far Northern Canada
by John M. MacFarlane 2014
The North Pole is the geographical &lasquo;top of the world’, 90 degrees north latitude, the point where all meridians of longitude intersect. The northernmost point on the globe, all directions are south from the North Pole. It is the northern end of the earth's axis. The region there receives six months of sunlight and six months of darkness. Along with the Northwest Passage the quest for the North Pole took on almost religious overtones.
The North Magnetic Pole is located between Greenland and the islands of the Canadian Arctic archipelago. The Pole itself migrates, constantly and daily. It causes a continuing error in charts and other navigation methods which depend on compass bearings. It was "discovered" by James Clark Ross in 1831. Observers know that they are at the North Magnetic Pole when a dip needle points vertically into the ground. The magnetic dip is 90 degrees where a suspended needle, able to point in any direction, points straight down.>/p>
Since that time the location has drifted more than 700km. It is thought that he drift is the result of fluctuations in the core of the electromagnetic field of the earth. The pole also ‘wobbles’, travelling around a closed path every day in a roughly elliptical shape which can be up to 100km across. This is thought to be the result of electromagnetic effects of electrical currents in the upper atmosphere caused by electrified particles flowing from the sun. There are several anomaly areas in the north which behave like ‘secondary magnetic poles’.
Magnetic storms are is temporary disturbances of the Earth’s magnetosphere. It can also create erratic behaviour in magnetic compasses in the northern regions. Systems that rely on satellites, such as Global Positioning System (GPS), are adversely affected when solar activity disrupts their signal propagation.
The earth's magnetism is based on electric currents set up by movement of the molten core of the earth. The magnetic field is similar in shape to that of a fleible slightly mobile axis of rotation of 15 degrees. The two poles are not quite antipodal (opposite each other). It is as if the axis of the earth’s magnet was slightly bent. The line joining them misses the exact centre of the earth, the reason is unknown.
A compass is unreliable at high altitudes. It only indicates true north when the observer is in line with the true north pole and the magnetic north pole. As the magnetic pole is approached the compass needle begins to dip down, until a horizontal force is too weak to vercome the friction in the compass's bearings. The needle becomes sluggish. Within 20 degrees of the magnetic pole the directive force is so weak that the compass becomes insensitive and unresponsive.
Prior to the development of GPS (Global Positioning System), navigators in the Arctic preferred to use gyroscopic compasses or to utilize sun navigation. Astro–Compasses (also known as Sun Compasses) are special instruments for making celestial or solar observations in the Arctic where there are areas of reduced compass reliability. Frequent checks are required to establish reliable position plotting for marine navigation. It is frequently utilized in northern latitudes where the use of GPS is not feasible. A sun compass is based upon a clock or a dial indicating local time which is set by hand.
To quote from this article please cite:
MacFarlane, John M. (2014) Navigating With Compasses in Far Northern Canada. Nauticapedia.ca 2014. http://nauticapedia.ca/Articles/Compasses_North.php