Basic Terrestrial Navigation Terminologies

Know all the Basic Terrestrial Navigation Terminologies – Improve Basic Navigation

 

Terrestrial Navigation-is the method of navigation in which the position is determined through  terrestrial objects/landmarks such as headlands, buoys, lighthouses, or any objects on the surface of the earth. 

To study Terrestrial navigation you must have grip on your basics of navigations which include knowing your earth, lat, long etc…
 
Let’s Begin…..
 

Shape Of Earth

The shape of earth was long known to be spherical as per Aristotle and Pythagoras;  the reason for their suggestion was based on the observation that it caused curve shadows during the lunar eclipses.

About 2000 years later Sir Issac Newton suggested that the earth is not a perfect sphere but it is a Oblate Spheroid i.e. flattened at its poles. The difference in axis is said to be about one part in three hundred.

The Equatorial diameter is 7926 miles and the polar diameter is 7900 miles.

This difference of 26 miles is because of Oblate Spheroid

For calculation purpose we take earth as a Sphere.

Terrestrial Navigation

 

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Great Circle

A great Circle is a Circle on the surface of a sphere whose plane passes through the center of the sphere.
 
A great Circle divides the sphere into two identical parts, each called as Hemisphere.
 
The radius of the Great Circle is equal to that of the Sphere.
 
Any number of Great Circle can pass through a given point on the surface of the sphere. However, all these G.C would also pass through a point diametrically opposite to the given point.
 
Only one G.C can pass through two given points on the surface of a sphere. However, if the two points are diametrically opposite to each other, any number of great circle can pass through the two points.
Terrestrial navigation

 

Small Circle

A small circle is a circle on a surface of a sphere, whose plane doesn’t pass through the center of the sphere.
 

Spherical Triangle

A spherical triangle is a figure formed on the sphere ( earth ) by three great circle arcs, all less than 180 degree. The sum of the angle is not fixed but always greater than 180 degree, 
 

If any side of the spherical triangle is 90 degree it is termed as Quadrantal.

Terrestrial navigation

 

 

Earth’s Axis

The earth rotates in its own axis and at the same time revolves around the sun in elliptical orbit.
 
The axis of rotation is not perpendicular to the plane of the orbit and it is inclined by an angle of 23.5 degree to the vertical.
 

The earth’s axis maintains its orientation in space i.e. it keeps pointing towards the same direction with respect to space

The fixed orientation and tilt of axis cause different seasons a earth orbit around the sun.

Terrestrial navigation

Poles

North Pole

The North Pole is located in the middle of the Arctic Ocean, and is known as the geographic north pole or terrestrial north pole. It is the point on the Northern Hemisphere where the earth’s axis of rotation meets the surface of earth.
 

South Pole

It is the opposite. The south pole is also known as the terrestrial or true south pole. It is one of the point where the earth’s axis of rotation meets the surface of the earth.

Equator

An imaginary circumferential line on the Earth’s surface equidistant from the true north and true south poles, dividing the earth into the northern and southern hemispheres.
 
It is about 40,075 km long and passes through 13 countries. 
 
78.7 % of the line lies across the waters and 21.3% across land. 
 
The plane of the equator passes through the center of the earth. 
 
It is also a reference of measuring latitudes 
 
It is the largest Great Circle.
earth
 

Meridians

Meridians is the half of a great circle drawn on the surface of the earth from the north pole to south pole. 
 
A meridian is also called a line of longitude and is half of a great circle. 
 

The meridians converge at the poles.

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Latitudes

Latitude is one of the two co-ordinate used to indicate the position of a person, or ship.
 
It is measured from 0 to 90 degrees from equator to poles  named North and South.
 
Hence 0 degree latitudes indicates all the places along the equator.
 
90N indicates North Pole and 90S indicates South pole.
 

Prime Meridian

The other coordinate used for indicating position on Earth is Longitude.
 
In case of longitude, the reference line taken is Prime Meridian
 
The Prime Meridian and its Anti Prime Meridian together forms Great Circle.
 
This G.C divides the earth into two parts namely Eastern and Western Hemisphere.
 

Longitude

It is one of the two coordinates of a place.
 
It can be defined as measure of the arc of the equator contained between the prime meridian and the meridian passing through that place.
 
It is named East or West.
 
A value of longitude cannot be more that 180 degree.
Prime meridian and Equator
 

Geographical Mile

It is the linear unit of length spanned by 1 minute of arc along the earth’s Equator. 
 
In SI unit it is 1855.3 meters. 
 
1 geographic mile = 1855 km

Statute Mile

The unit of distance measured on land equal to 1760 yards.
 
1 statute mile = 1609 km

Nautical Mile

Or Sea Mile is a unit of distance set by International agreement as being exactly 1852 km.
 
It was defined as the distance spanned by one minute of arc along a meridian of the earth.
 
1 nm = 1852 km

Difference of Latitude

It is the number of degrees by which two parallels of latitude are separated from each other. 
 
The D’Lat can have a name of N and S.

Difference of Longitude

It is the number of degrees by which two meridians are separated from each other.
 
The D’Long can have a name of E and W.
Difference in longitude
 

Knot

It is a unit of speed used by navigatotd of onne nautical mile per hour 
 
The standard symvbol is kn.
 

Cable

It is a nautical unit of length equal to one length of a nautical mile or 185.2 m or also termed as 100 fathoms.

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