Change of Declination in Time and Space
Simply speaking, true north is the direction in which the north pole is located along the Earth's rotational axis, while magnetic north is the direction toward which the compass needle points.
Magnetic declination varies both from place to place and with the passage of time. As a traveller cruises the east coast of the United States, for example, the declination varies from 20 degrees west (in Maine) to zero (in Florida), to 10 degrees east (in Texas), meaning a compass adjusted at the beginning of the journey would have a true north error of over 30 degrees if not adjusted for the changing declination. In the UK it is one degree 34 minutes west (London), and as the country is quite small that figure is fairly good for the whole of the country. It is reducing, and in about 2050 it will be zero.
In most areas, the spatial variation reflects the irregularities of the flows deep in the earth; in some areas, deposits of iron ore or magnetite in the Earth's crust may contribute strongly to the declination. Similarly, secular changes to these flows result in slow changes to the field strength and direction at the same point on the Earth.
The magnetic declination in a given area may (most likely will) change slowly over time, possibly as little as 2–2.5 degrees every hundred years or so, depending upon how far from the magnetic poles it is. For a location closer to the pole like Ivujivik, the declination may change by 1 degree every three years. This may be insignificant to most travellers, but can be important if using magnetic bearings from old charts or metes (directions) in old deeds for locating places with any precision.
Read more about this topic: Magnetic Declination
Famous quotes containing the words change of, change, time and/or space:
“The most advanced nations are always those who navigate the most. The power which the sea requires in the sailor makes a man of him very fast, and the change of shores and population clears his head of much nonsense of his wigwam.”
—Ralph Waldo Emerson (1803–1882)
“—No, no thou hast not felt the lapse of hours!
For what wears out the life of mortal men?
‘Tis that from change to change their being rolls;
‘Tis that repeated shocks, again, again,
Exhaust the energy of strongest souls
And numb the elastic powers.”
—Matthew Arnold (1822–1888)
“A poem is like a person. Though it has a family tree, it is important not because of its ancestors but because of its individuality. The poem, like any human being, is something more than its most complete analysis. Like any human being, it gives a sense of unified individuality which no summary of its qualities can reproduce; and at the same time a sense of variety which is beyond satisfactory final analysis.”
—Donald Stauffer (b. 1930)
“Oh, my. I’d forgotten how much I hate space travel.”
—George Lucas (b. 1944)