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In Europe, the concept of declination was known in the early 1400s, but the first precise measurement of declination was not made until 1510, when Georg Hartman determined the declination in Rome.The importance of declination for navigation was obvious.It can be seen that in Southern Canada users of such compasses will seldom experience fluctuations larger than 2 degrees.However, someone on a canoe trip in the would find his or her compass in error by more than 2 degrees on more than 1 day in 4.Mariners quickly devised methods for determining it and began compiling declination values from locations around the world.In 1700 Edmund Halley came up with the idea of showing declination as contour lines on a map ; he used this novel concept to produced the first declination chart of the Atlantic Ocean.The diagram shows the percentage of days in a typical year during which magnetic declination will fluctuate by more than a given amount from its normal value.
The angle between magnetic north and true north is called magnetic declination.
Changes in declination become increasingly irregular in both amplitude and frequency as one approaches the North Magnetic Pole, a result of the weak horizontal component of the magnetic field.
The number of times per year that a compass user will be affected by changes in declination caused by magnetic storms will depend both on the user's application and location.
Magnetic declination also undergoes changes that are much more rapid than secular variation and are a result of magnetic activity.
These variations can be smooth and cyclic, with amplitudes of several minutes of arc in southern Canada, or, during magnetic storms, large and erratic.
Declination charts have been produced on a regular basis ever since.