MAGNETIC DECLINATION
DIRECTION
Magnetic North is the direction the needle of a compass points to. True North is the direction from a given location to the geographic North Pole (see THE THREE NORTHS).
The North Pole is stationary whereas the Magnetic North Pole wanders over the Arctic Ocean. In general, Magnetic North and True North at a given location do not align: the angle between True North and Magnetic North is called Magnetic Declination.
Magnetic Declination is called Magnetic Variation by pilots and mariners.
MAGNETIC DECLINATION
Magnetic Declination varies from place to place and with time; it can be positive or negative.
Magnetic Declination can be measured and modelled. The models are revised every five years as the Earth’s magnetic field of the Earth is constantly changing.
MAGNETIC DECLINATION MAP
The National Oceanic and Atmospheric Administration (NOAA) publishes magnetic field maps (choose Declination – Main Field ).
MAGNETIC DECLINATION CALCULATORS
- Geoscience Australia: Australian Geomagnetic Reference Field Values
- NOAA – National Centers for Environmental Information: Magnetic Field Calculators
POSITIVE/NEGATIVE MAGNETIC DECLINATION
By convention, the north-south line is the reference direction and angles are always measured clockwise from the reference direction.
POSITIVE MAGNETIC DECLINATION
Magnetic Declination is positive when the Magnetic North moves in an easterly direction (clockwise): it is to the east of True North.
Magnetic North is east of True North: the Magnetic Declination (D) is positive.
NEGATIVE MAGNETIC DECLINATION
The Magnetic Declination is negative when the Magnetic North moves in an westerly direction (anticlockwise): it is to the west of True North.
Magnetic North is west of True North: the Magnetic Declination (D) is negative.
NULL MAGNETIC DECLINATION
In some locations on Earth, the Magnetic Declination is equal to zero: Magnetic North and True North are aligned.
MAGNETIC DECLINATION IN AUSTRALIA
The lines show areas of constant magnetic declination. Positive declinations are coloured red, negative declinations blue. The green line of zero declination is called the agonic line.
The magnetic variation varies across Australia from about -2.5° in Western Australia to about +15° in Tasmania. For most of the continent the magnetic deviation is positive except in parts of Western Australia where is is negative.
The magnetic declination in Sydney can be estimated on the map as 12.5° (at the time of writing, it is 12.78°) and the declination is positive.
IN SUMMARY
The angle between True North and Magnetic North is called the Magnetic Declination or Variation.
Magnetic Declination varies from place to place and with time; it can be:
- positive: Magnetic North moves in an easterly direction or,
- negative: Magnetic North moves in an westerly direction.
