How the Magnetic compass is used for direction finding..!!

What is Magnetic compass, or how Magnetic compass is used for direction finding

We have a lot of doubts when it comes to the magnetic compass. Doubts like, What is a Magnetic compass or What is magnetic compass is used for. Or how does a magnetic compass work.

Lets get to know that Magnetic compass is a device used for direction finding, using the magnetic properties of the earth.

While the working of the magnetic compass is explained in further paragraphs.

It’s mainly used for navigation onboard aircraft’s and onboard ships.

Magnetic compass in Navigation

As you can guess, that we don’t need it on land as much as we need it on water or in air.

On land, we already have roads, bridges, pathways. Which are already there built by our governments.

While In water, there are no roads, no pathways. And once you are in open sea, There are no landmarks either which can help us in navigation.

Let’s say for and example, that we departed on our ship from Mumbai(India) and we need to reach Sohar(Oman).

So till the time local pilot is onboard, he will assist us in navigation to reach the pilot station. Outside which we don’t need any person or pilot with local knowledge.

Till next few miles, we have landmarks or other objects which will be helpful for safe navigation.

Now when we have come out at sea, far enough from the land. And we don’t have any landmarks for navigation.

On our plan we have marked a line from Mumbai to Sohar. Suppose we have to go in 275 degrees direction. Which is slightly away from “West”.

Out at sea, when we have compass, we know exactly in which direction we should head for.

That way we can easily navigate in open seas. So the magnetic compass is used for direction finding at sea, in air or even on land.


The another compass used for navigation in Gyro compass. Which was built to help us in precise navigation.

So the compasses are built to assist the navigators in the accurate navigation.

Let’s try to know the magnetic compass a little better-

Magnetic compass marked into how many degrees

Actually the magnetic compass is divided into 360 degrees. Which is 0 to 360.

In which 0 degree is marked towards North direction.

90 degree is towards east direction.

180 degree marks south and 270 degree is marked towards west direction.

So if you are looking at our magnetic compass, and it is showing 0 degree. Then it means our ship is heading in north direction.

Same way is applicable for the other directions mentioned above.

And since we don’t always head in perfect north, east, south or west direction.

That’s why it is divided into 360 degrees. Which help the ship in heading in a precise direction.

Suppose we have to head into 100 degrees, which is a little away from east direction. So with the help of magnetic compass, we can head into the exact direction we need to.

Same is applicable with aircrafts navigation.

Magnetic compass principle

magnetic compass principle is based upon two of its properties. Which uses earths magnetism for direction finding.

Therese properties of magnetic compass are as below-

1. When you suspend a magnet freely, it aligns itself with the magnetic meridian. With red pile of the magnet towards the north magnetic pole of the earth. While the Blue pole to the south magnetic pole of the earth.

2. Like poles repel each other and unlike poles attract each other.

We know now that the Magnetic compass is used onboard ships for what purpose.

Basically it is a tool, which assists the vessel in determining its heading. It in simple language you can say that it tells the ship, in which direction it is heading.

So now let’s come to the working of the magnetic compass. Lets see how the magnetic compass is used for finding the direction even at open sea.

How does the magnetic compass work?

Magnetic compass uses the magnetism of Earth to find the direction.

The earth has part liquid and part solid iron inside.
The solid core is at the centre, while the liquid core is outside the solid core.

So the movement of the liquid causes the magnetic field of the earth.

While on the other hand, due to the magnetic field, earth has two magnetic poles.

The poles are named North Pole and the South Pole.

The other important thing to be noticed is that these magnetic poles are near to the geographic poles of the earth.

While magnetic poles are built because of the magnetism of the earth, the geographic poles are the North Pole and South Pole which are named because of the geography of the earth.

Now if we talk about a compass, it is basically a needle which is magnetised.

As the compass needle is magnetized, it works well as a magnet and thus the South Pole of the compass/needle points towards the North magnetic Pole of the earth.

Geographic poles

Geographic poles are the North Pole and the South Pole of the earth.

These poles have been determined because of the geography of the earth.

The earth has been divided virtually into two semi spheres. The plane dividing the earth in two parts is called “Equator”.

So there are almost two identical semi spheres on both sides of this equator.

Now let’s we take one axis perpendicular to the equator, and pass it through the centre of the earth.

This axis intersects the surface of the earth at two points.

These intersections are named as the North Pole and the South Pole.

Magnetic poles

As we discussed about the geographic poles earlier. Which are based upon the geography of the earth. And thus the location of the geographic poles never changes.

While on the other hand, the magnetic poles are North magnetic pole and the South magnetic pole. Which are generated because of the magnetic field of the earth.

There is another thing to be noted. It is that the Earth’s magnetic field is caused by the forces generated by some internal reactions at the centre of the earth.

These forces keep changing with time, and thus the magnetic field of the earth also changes in intensity.

So the change in the strength of the magnetic field causes the Magnetic poles to shift their location gradually.

That is the reason that magnetic poles are changing their locations on continuous basis, while the geographic poles are steady.

Magnetic compass invention

The first magnetic compass ever was used was invented by Han dynasty in China in 202 BC-220 AD.

They used a magnetised piece of iron(also called lodestone) as a compass. Which also used the magnetism of earth.

Later the compass was used by Song Dynasty of China. They used the compass needle in a bowl of water.

As the bowl of water did not have any friction and thus the needle pointed to the magnetic poles moving freely. Thus assisting the navigators with the directions.

Later on the improvised versions were used by the Europeans and then the rest of the world.

Magnetic compass SOLAS requirement

Carriage of a standard magnetic compass is a requirement under SOLAS Reg.V/19.

It states that- All ships irrespective of the size should have:

A properly adjusted standard magnetic compass, or other means, independent of any power supply to determine the ships heading and display the reading at main steering position.

There should be a compass bearing device too, which should provide bearing on an arc of 360 degrees.

Means of correcting heading and bearing to true at all times.

While all ships of 150 GRT and above and all passenger ships irrespective of their size should have an Spare magnetic compass interchangeable with the main magnetic compass.

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