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:
“To the sick the doctors wisely recommend a change of air and scenery.”
—Henry David Thoreau (1817–1862)
“It is easier to move rivers and mountains than to change a person’s basic nature.”
—Chinese proverb.
““Come, come” said Tom’s father, “at your time of life,
There’s no longer excuse for thus playing the rake—
It is time you should think, boy, of taking a wife.”
“Why, so it is, father—whose wife shall I take?””
—Thomas Moore (1779–1852)
“I would have broke mine eye-strings, cracked them, but
To look upon him, till the diminution
Of space had pointed him sharp as my needle;
Nay, followed him till he had melted from
The smallness of a gnat to air, and then
Have turned mine eye and wept.”
—William Shakespeare (1564–1616)