Discovery of the Coincidence of Magnetic and True North

Magnetic Earth

Rounding the southern coast of Africa in the 1480s and 1490s, Portuguese navigators discovered one point where magnetic north and true north were virtually identical. They called this place the "Cape of the Needles" (Cabo das Agulhas) because around 1500 all compass needles used here pointed to true north.
On this 1516 map, Cape Agulhas is clearly marked with the compass needle pointing due north.

As you can see from this map, and our visit to the sign below, Portuguese sailors knew this so well that they had it on all their maps!

Cape Agulhas, the southern most point of the African continent today.

It's right here!

Facts on Magnetism and the Earth
Earth's Magnetic Field The earth's magnetic field results from electric currents in the earth's spinning molten iron core. As a result, magnetic north is constantly changing.
Compass needles point to magnetic north, more or less. Moreover, magnetic north is close to, but not exactly, north. Sailors call the difference between true north and magnetic north "magnetic deviation" (to distinguish it from other possibly deviant activities). Others call this difference "magnetic declination."
Electromagnetic Storms The earth's regular magnetic patterns are sometimes suddenly disrupted by sudden magnetic storms caused by energy flaring out of the sun. The earth's magnetic fields sometimes trap huge plasma bubbles traveling at 500 miles a second from the sun. These bubbles interact with the earth's northern magnetic field to produce the brilliant light curtain called the aurora borealis or Northern Lights. On the down side, the storms cause power outages and radiation exposure. They can interfere with communication from satellites (including Global Positioning Satellites) and cause inaccurate magnetic readings even from simple compasses.

Fifteenth-century Portuguese navigators in the fifteenth century turned to celestial navigation because they realized how unreliable magnetic information was.
By the early sixteenth century, they had large amounts of data on magnetic changes in the Atlantic.

Available Elsewhere on the Net
Geomagnetism FAQ | Where Magnetic North is today (more or less)) | Correcting a Compass to find true north | Magnetic Fields from space
Is a Geomagnetic Storm coming your way soon? | Marvelous Magnetic Maps | Detailed Marine Magnetic Data (for sale) |
History: How Magnetic North has Changed Database with Historical Data on Changes in Magnetism (The best information is under Flash Maps)| Magnetic Changes and How Fast Plates are moving |


Home page | The Agulhas Current