Magnatic_field_of_the_earth-study_probe

It is known to everybody that shape of the earth is spherical, or sometimes it is called oblet spheroid type. Thenceforth we can divide the earth into four hemispheres, viz. northern hemisphere, southern hemisphere, eastern hemisphere, and western hemisphere. Thus simply the northern part of north hemisphere indicates the north direction, and this way the southern part of south hemisphere indicates the south direction. But that is not everything about it. If we consider the north direction, there are two types of indication. First one is Geographic North, and second one is Magnetic North.

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What's the difference between Geographic North and Magnetic North?

The earth rotates on its own axis, and the two end points of the axis is called the geographic poles, that is North and South Pole.

‘Geographic North’ indicates the fixed point at the north pole of earth, that is 90°N. It is also called the ‘True North’.

Accordingly, for that of the south, it is called Geographic or True South as well. In other words, these are the two points in the two opposite poles where all the longitudes meet together (at 90°N/S).

Earth has a strong magnetic field that is generated due to the presence of charged particles in the core area of the earth. The mechanism behind it is called the ‘Dynamo Effect’, which depicts the formation of earth's magnetic field. Hence the earth acts as a giant magnetic spheroid with north and south poles, wandering in the universe.

Magnatic_and_true_north-study_probe
A graphic presentation of the Earth's Magnetic Field

But this magnetic north and south points are not exactly coincide with the perfect 90°N/S like geographic north or south. There exists a distortion between these two types at the poles. Thenceforth this different north point indication, caused due to the magnetic field of the earth, is known as ‘Magnetic North’.

Note to the fact, the imaginary line joining the magnetic north and magnetic south is inclined at an angle compared to the axis joining the true or geographic north and south. The angle forms between these two is known as ‘Magnetic Declination’.

The axis joining the geographic north and south is called ‘Geographical Meridian’, and for that of the magnetic north and south, is called the ‘Magnetic Meridian’.

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Variation of Magnetic Declination

Depending on your location, your magnetic compass will have more or less error which referred to as ‘Variation’. This variation increases towards the poles. That means, of you are in the polar region, then magnetic declination of your compass will be more than that of if you are in lower latitude regions. So navigation through a compass becomes problematic towards the poles.

At the lower latitude regions, there will be a mild error which can be dealt with by adjusting the compass needle.


How to convert a magnetic north to a true north?

First of all you need to know about your exact location on a magnetic declination map like the following one.

World_Magnetic_Declination_2010
Magnetic Declination Map | Image courtesy : Wikimedia

Click the following link to directly get access to the Magnetic Declination measures by NOAA.


Now, if you are in the eastern hemisphere, then true north will be east of the compass needle by the number of degrees shown on the map for your location.

In the other side, of you are in the western hemisphere, then geographic north or true north will be west of the compass needle by the number of degrees shown on the map for your location.

By the way, it is important to note that, this declination varies over time to time, because earth's magnetic field wobbles around the poles. And also you should be aware of that some areas on the earth surface have its own local magnetic variation. That are marked on geological survey maps.

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