Sailors have a long relationship with compasses and magnetism. I even have a compass on my Laser. But the earth's magnetic field has always struck me as an exceedingly weird phenomenon. Some of the strange things about it include...
- That it should exist at all. If it didn't we wouldn't, "they" say. Amazing!
- "They" say it is caused by "electrical currents produced by the coupling of convective effects and rotation in the earth's spinning liquid metallic outer core of iron and nickel." A likely story!
- The magnetic poles are not aligned with the geographic poles. How odd! Why not? I have no clue. The map above shows magnetic declination, how much the direction a compass points differs from true north, at different points on the earth.
- There are actually two pairs of magnetic poles. The "magnetic poles" are the two positions on the Earth's surface where the magnetic field is entirely vertical. The two positions where the axis of the dipole that best fits the Earth's field intersect the Earth's surface are called the "geomagnetic poles." They are not in the same place as the magnetic poles. Seriously weird!
- The magnetic poles are not at directly opposite positions on the globe. Crazy! How can that be?
- The magnetic poles move around over time. Spooky! What makes that happen?
- On average about every 300,000 years the earth's magnetic field reverses itself. Crazy! Who would have guessed that?
- But the last reversal was 780,000 years ago. Sounds like we are overdue for another reversal. Watch this space. I will definitely blog about it when it happens. (As long as it's before the Rapture.)
- Some animals and birds can detect the earth's magnetic field. Birds use a magnetometer in their beaks.
- Some people think the iPhone compass detects the earth's magnetic field. But the real explanation of how it works is here.
How strange is that possum?