Direction
Direction of an object or a point on the Earth is called the relative position of the object in comparison to another object that is considered to be the initial, without taking under consideration, as a criterion, the distance between them. The most definite and practically comprehensible direction is the one that is oriented in the North- South direction.
The Northern direction is represented on the terrestrial sphere by the tangent on the meridian of a specific area. It is called ‘meridian line’.
According to these, we have the north direction and its opposite, the south direction. The direction to the side that the sun and the stars rise, namely the right side as we look to the North is called ‘east direction’. The opposite direction, to the side that the sun and the stars set, the left side as we look to the North, is called ‘west direction’.
In navigation, direction is counted in degrees starting from the north direction or the direction of the vessel’s bow.
Three directions are in use:
True north
Is the direction of the North pole of the earth, that results for every place by the meridian line of the place, namely the tangent of the meridian on the place.
Magnetic North
Is the direction pointed by the magnetic needle when affected only by the Earth’s magnetic field, given that in the universe the Earth behaves like a giant magnet that attracts and is being attracted by the celestial bodies.
Compass North
It is the direction shown by the magnetic needle when affected both by the Earth’s magnetic field and the magnetic field of the iron vessel it belongs.
The direction of the ship’s bow is represented by its longitudinal, which is the imaginary line between bow and stern.
Variation
It is the angle formed between the True North and the Magnetic North. It is defined as East or West if the Magnetic North is situated on the right or on the left of the True north respectively.
Variation alters:
1. From place to place
2. Because of time variations
3. Because of magnetic disturbances
The value of the variation of a specific place and time can be computed.
Deviation
It is the angle formed between the Right Magnetic North and the Compass North. It is defined as East or West if the Compass North is situated on the right or the left of the Magnetic North respectively.
Deviation alters:
1. From compass to compass
2. By the course of the vessel
The value of deviation is indicated by the compass deviation card, a specialized table that every vessel has to be equiped with.
Compass Error
It is the angle formed between the True North and the Compass North. It is defined as East or West.
Compass Error is the algebraic sum of Variation and Deviation according to which the indications of the compasses are corrected in order to respond to the real measurements and vice versa.