Why do seafarers use a compass

Compass and orientation

Without him, Christopher Columbus would have got lost in the Atlantic, Ferdinand Magellan's ships would never have circumnavigated the world. Seafarers have been using the compass for orientation for over a thousand years. But how could this little thing show them the long way across the oceans?

The secret of the compass was only revealed very late: in 1600, the English scientist William Gilbert was the first to give a reasonable explanation for the ability of the compass needle to orient itself in a north-south direction: the earth itself is magnetic. The compass needle simply aligns itself with the magnet earth. And thus helps people to find their way around.

Nobody can get lost with a compass and map in their luggage - provided they know how they work together. The compass consists of a magnetized steel needle, which sits freely movable in its center on a tip. Similar to the hands of a clock on the dial, this tip is attached to a scale with all four cardinal points. If the compass is horizontal and steady, its magnetic needle aligns itself with the field lines of the earth's magnetic field: it points in a north-south direction. If you put a map under the compass and turn it until its north direction points in the same direction as the compass needle, the map is north. The direction of the destination is now easy to see.

But there is one small difficulty: Because the magnetic poles of the earth are constantly moving, the magnetic pole and the geographical pole do not exactly match. This leads to an angle difference between the two poles. This so-called declination has to be taken into account when using a compass and it is not the same everywhere on earth. Here in Germany, the magnetic declination is relatively low and is approximately between 1 ° and 3 ° in an easterly direction.

Not only humans but also animals orientate themselves on the earth's magnetic field. Many animal species undertake long migrations during the year, for example migratory birds. To find the long way south, they orientate themselves on the landscape, the position of the sun and at night on the stars. In addition, they have their own magnetic sense, which gives them the direction. With this "compass in the body" you can find the right way even in poor visibility.

Magnet earth

We don't notice it, but the compass needle clearly shows us that the earth is a giant magnet. It has two magnetic poles, a north pole and a south pole. And like all magnets, the earth is surrounded by a magnetic field: the earth's magnetic field.

In the area of ​​its magnetic field, a magnet exerts force on other magnets, for example on a compass needle. The effect of a magnet can also be made visible through fine iron filings: They are arranged around the magnet and point in the direction of its two poles. A line-like pattern is created that shows the magnetic forces. The lines of this magnetic field are the so-called field lines.

The earth's magnetic field also has such field lines. They emerge from the earth near the south pole, run outside the earth to the north pole and disappear there again into the earth. So they are arranged as if a giant bar magnet were pulling through the middle of the earth.

The south pole of this imaginary bar magnet points roughly to the geographic north pole, its north pole to the geographic south pole. What sounds confusing at first has a simple explanation: the north and south poles attract each other. That is why the north pole of the compass needle points to the magnetic south pole of the earth, the south pole on the needle points to the magnetic north pole.

The earth's magnetic field is not only used for orientation on this planet. Together with the atmosphere, it also protects us from dangers from space. One of these threats is a stream of charged particles that the sun is constantly ejecting in all directions. This so-called solar wind is deflected by the earth's magnetic field. Like a capsule, the earth's magnetic field redirects the charged particles so that they fly past the earth and can no longer be dangerous for us.


On an Arctic expedition, polar explorer James Clark Ross discovered the magnetic south pole. His measuring instruments had shown him the way. The magnetic pole is on mainland Canada, about 2,300 kilometers from the geographic North Pole.

In May 1829, the British polar explorer John Ross set off on an expedition to the Arctic with his nephew James Clark Ross. The goal of the two researchers was the Northwest Passage. It is a sea route north of the American continent, which leads through the middle of the icy Arctic Ocean. When the two researchers reached a peninsula with their sailing ships, they realized: They had reached the northernmost point of the American continent. Because of the huge ice masses and because of technical problems with the ships, they were stuck there. While exploring the mainland, James Clark Ross realized that they were near the South Magnetic Pole. With the help of local Inuit, he set off on sledges and reached the Magnetic South Pole on June 1, 1831. The geographic North Pole was about 2,300 kilometers away from them. This makes the Briton James Clark Ross the first European to be at the magnetic south pole.

When and how the expedition with the research duo Ross will return to Europe is currently not known due to ongoing technical problems.

The Boothia Peninsula

Boothia is the name of the peninsula that polar explorer John Ross discovered in the north of mainland Canada. He named it after his friend, the gin maker Felix Booth. This wealthy English businessman had largely paid for the polar expedition.

The Boothia peninsula is barren: tundra and bare frost debris and rock form the landscape. This is where the Inuit are at home, an ethnic group that is also native to Greenland. They live mainly from hunting seals, whales or polar bears and from fishing. Their means of transportation are kayaks and dog-drawn sleds. It was only with the support of these natives that James Clark Ross was able to reach the magnetic south pole.


Big reception in the Spanish port of Sanlúcar: after almost three years, the “Victoria” is returning from her expedition. But the joy is clouded. Of the five ships in the fleet, only this one comes back, and of the 237 crew only 18 survived. The leader of the expedition, the Portuguese Ferdinand Magellan (42), was also killed on the way.

So he could no longer experience the great triumph himself: his expedition succeeded for the first time in the history of mankind to completely circumnavigate the world! Ferdinand Magellan set out from Seville with his five ships on August 10, 1519. He was on the way on behalf of the Spanish Crown to find the western route to the lucrative Spice Islands in the Pacific Ocean. This was necessary after the competing sea power Portugal had taken the sea route in an easterly direction around the African Cape of Good Hope.

After an arduous search, Magellan and his team discovered the long-awaited “Gateway to the West” on the southern tip of South America. At the end of November 1520, they sailed through a narrow 600-kilometer strait into the Pacific Ocean.

But the setbacks were inevitable. In an attempt to take islands of the newly discovered Philippines for the Spanish crown, Captain Magellan fell victim to the lances and poison arrows of the natives. Numerous crew members died with him in the fighting, others had died in the months before from the catastrophic supply situation on the ships. One crew member reported that they had to eat leather and rats cooked in salt water. Many died of scurvy.

But the survivors can be proud of themselves. You are the first to travel around the world. So they provided the final proof: the earth is a sphere. And in addition to fame, honor and knowledge, they brought home over 26 tons of valuable spices.

Globe larger than expected

The logbook entries of the "Victoria" will now give the scientists some homework. It seems that up to now the extent of the earth has been underestimated.

The most prominent victim of this misjudgment was Christopher Columbus. He also wanted to find the western route to India, but assumed about a quarter less circumference of the earth. At that time, nothing at all was known about the new continent in the west, Asia was assessed as too big and the Pacific Ocean as too small. When he came across the Bahamas in 1492, he was convinced that he had discovered "India".

Now it looks like the Greek scientist Eratosthenes was right. As early as 240 BC he had taken measurements using the simplest of methods and calculated a circumference of around forty thousand kilometers from them.


Robins can perceive a magnetic field and use it for orientation. The Frankfurt ornithologist Wolfgang Wiltschko has proven this through experiments. How the magnetic sense of migratory birds works exactly has not yet been researched.

In autumn, many robins regularly move to warmer latitudes - to the southwest towards Spain and northern Africa. To find their way there, the migratory birds use the sun during the day and the stars at night. But what if fog and clouds block the view of the stars? The biologist Wolfgang Wiltschko asked himself that too.

To get to the bottom of the secret, he constructed a special cage in the basement of the Frankfurt Zoo. On the one hand, this can be shielded from the earth's magnetic field, but it can also create a weak artificial magnetic field. In this windowless cage he put the robins. The result: if the magnetic field was virtually switched off, the birds fluttered wildly around each other. If, on the other hand, an artificial magnetic field was generated in the cage, the animals only wanted to fly in one direction: that which corresponded to the south-west in the artificial system.

With this experiment, Wiltschko was the first researcher to succeed in demonstrating a magnetic sense in animals. But where is this compass located in the body and how exactly does it work? The newly discovered sense organ still poses many questions to science.

Where does the robin go?

The robin is best known to us with its orange-red front part. It is trusting, eats insects and small worms and sings from morning to night. But does it actually stay with us in winter? Or is it a migratory bird? The answer is: It depends. Because the robin is widespread and lives in large parts of Europe and Asia Minor. The robin also spends the winter in the warmer regions, where it is a resident bird. Here in Central Europe, only some of the robins migrate to the western Mediterranean, some overwinter. So here it is a typical partial puller. And only the robins that inhabit Eastern and Northern Europe are real migratory birds: They clear the field in October and only return to their breeding area in March.