The circumnavigators are back

A big welcome in the Spanish port of Sanlúcar: after almost three years, the “Victoria” returns from its expedition. But the joy is clouded. Of the five ships in the fleet, only this one returns, and of the 237 crew only 18 have survived. The leader of the expedition, the Portuguese Ferdinand Magellan (42), also died on the way.

So he was unable to experience the great triumph himself: his expedition succeeded in completely circumnavigating the globe for the first time in human history! Ferdinand Magellan set out from Seville with his five ships on 10 August 1519. He was on his 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 rival sea power Portugal had seized the sea route in an easterly direction around the African Cape of Good Hope for itself.

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

But setbacks were not lacking. In an attempt to capture islands in the newly discovered Philippines for the Spanish crown, Captain Magellan fell victim to the lances and poisoned arrows of the natives. Numerous crew members died with him in the fighting, others already in the months before from the catastrophic supply situation on the ships. One crew member reports that they had to live on leather boiled in salt water and rats. Many died of scurvy.

But the survivors can be proud of themselves. They are the first people to travel once around the world. Thus they provided the final proof: the earth is a sphere. And in addition to fame, honour and knowledge, they brought home over 26 tonnes of valuable spices.

Earth sphere larger than suspected

The logbook entries of the “Victoria” will now give the scientists some homework. It seems that so far, the size of the Earth has been underestimated.

The most prominent victim of this misjudgement was Christopher Columbus. He also wanted to find the western route to India, but assumed about a quarter less of the earth’s circumference. At that time, nothing at all was known about the new continent in the west, Asia was considered too large and the Pacific Ocean too small. When he came across the Bahamas in 1492, he was therefore firmly convinced that he had discovered “India”.

Now it looks as if the Greek scientist Eratosthenes was right. As early as 240 BC, he had taken measurements using the simplest methods and calculated a circumference of about forty thousand kilometres.

Why is the earth round?

Geellllaa, [25.11.2022 17:38]
What happens if you always go in the same direction? Do you eventually reach the edge of the world or is the world infinite?” More than 2300 years ago, the famous Greek scientist Aristotle was already sure: neither one nor the other. Because the earth is not flat like a disc, but a sphere – but why?

Geellllaa, [25.11.2022 17:38]
To understand this, you have to go back to the time when the earth was formed. The force that was responsible for this is gravity – all massive objects attract each other. This force made pieces of rock collide and combine to form a planet. And it gave the planet its shape. Because gravity works equally strongly in all directions.

Geellllaa, [25.11.2022 17:39]
Since the earth was hot and liquid at the beginning, the material was able to flow into the shape that gravity dictated. If a piece of earth material moved further out somewhere, it was attracted by the rest until the surface was smooth and the same force of gravity worked in all places. And since gravity is the same in all directions, the shape of a sphere automatically emerged – because only with a sphere are all points on its surface equidistant from the centre of gravity.

But if you look very closely at the shape of the Earth, you will see that it is not a perfect sphere: it is slightly flattened at its poles and somewhat bulbous at the equator.

This is due to the Earth’s rotation: in the course of 24 hours, the Earth rotates once around its axis. This rotation creates a force called centrifugal force. We know this from the chain carousel when we fly outwards on the swings. In the case of the Earth, the centrifugal force causes the rock masses to slide outwards a little from the axis of rotation, i.e. from the poles towards the equator. There, the diameter of the earth is about 41 kilometres larger than between the north and south poles.

Compass and orientation

Without it, Christopher Columbus would have got lost on the Atlantic, Ferdinand Magellan’s ships would never have sailed around the world. For over a thousand years, sailors have used the compass for orientation. 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 compass needle’s property of aligning itself in a north-south direction: The earth itself is magnetic. The compass needle simply aligns itself with the earth’s magnet. And thus helps people to orient themselves.

So with compass and map in your luggage, no one can get lost – provided you know how their interaction works. The compass consists of a magnetised steel needle that sits freely movable on a point in its centre. Similar to the hands of a watch on the dial, this tip is placed on a scale with all four cardinal points. When the compass is horizontal and still, its magnetic needle aligns itself with the field lines of the earth’s magnetic field: It points in a north-south direction. If you place a map under the compass and turn it until its north direction points in the same direction as the compass needle, the map is aligned. 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 coincide exactly. This leads to an angular difference between the two poles. This so-called declination must be taken into account when using a compass, and it is not the same everywhere on earth. Here in Germany, the declination is relatively small and is approximately between 1° and 3° to the east.

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