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A scientist has made the first measurements of the strength at the Earth’s core of its magnetic field. What’s most fascinating is that he used the Moon and distant quasars to do it! First he used radio observations of the quasars to get very precise measurements of the Earth’s rotation axis and how the Moon was tugging at that axis and thus affecting its magnetic field. Then,
By calculating the effect of the moon on the spinning inner core, Buffett discovered that the precession makes the slightly out-of-round inner core generate shear waves in the liquid outer core. These waves of molten iron and nickel move within a tight cone only 30 to 40 meters thick, interacting with the magnetic field to produce an electric current that heats the liquid. This serves to damp the precession of the rotation axis. The damping causes the precession to lag behind the moon as it orbits the earth. A measurement of the lag allowed Buffett to calculate the magnitude of the damping and thus of the magnetic field inside the outer core.