Where compasses fail: What are the ‘blackout zones’?
For centuries, the compass was an indispensable tool for sailors, explorers and travellers. Its simple operation relies on the Earth’s magnetic field: a magnetic needle freely rotates around a pivot and always points north. Yet there are places on our planet where this system completely fails: experts refer to these as “blackout zones”.
The poles: where compasses go haywire
The World Magnetic Model precisely identifies regions where compasses become unreliable. The largest of these areas are found around the North and South Poles.
This is due to the behaviour of the Earth’s magnetic field. In mid-latitudes, magnetic field lines run at a shallow angle, allowing the needle to remain level and consistently point north. Near the poles, however, these lines plunge almost vertically into the Earth’s interior. As a result, the needle may tilt downward, stick, or spin erratically, rendering our once-trusty device useless.
Underground iron ore and magnetic anomalies
Issues aren’t limited to the polar regions. Certain places exist where minerals in the ground disrupt magnetic orientation. A classic example is Russia’s Kursk region, home to vast iron ore deposits. As early as 1784, it was observed that compasses there deviated from the usual northward direction. According to a 1949 report by the CIA, such occurrences are classified as magnetic anomalies.
A similar discrepancy has been detected around Bangui, the capital of the Central African Republic. In this case, however, scientists have yet to determine a clear explanation. One theory suggests an ancient meteor impact may be to blame, as the explosive collision could have altered the local rock formations and their magnetic properties.
What about in space?
In theory, a compass could also function near the Earth, within the so-called magnetosphere. This invisible magnetic “bubble” extends up to around 37,000 kilometres on the sunward side and stretches as far as 370,000 kilometres in the opposite direction.
In practice, however, the magnetic field in space is far weaker and significantly more irregular than on Earth’s surface. Solar wind constantly distorts and reshapes it, causing a compass needle to jitter and deliver unreliable readings. This is why astronauts never bring compasses with them; instead, they rely on advanced navigational instruments.
Throughout history, the compass has been a fundamental navigation tool, but today we know that it becomes entirely ineffective in certain parts of the world. The polar regions and unusual magnetic anomalies demonstrate that the Earth’s magnetic field is far from uniform.
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