Is the Earth a magnet?

At most places on the Earth's surface, the compass doesn't point exactly toward geographic north. The deviation of the compass from true north is an angle called "declination" (or "magnetic declination"). It is a quantity that has been a nuisance to navigators for centuries, especially since it varies with both geographic location and time . It might surprise you to know that at very high...

A diagram at the bottom of most USGS topographic maps shows three north arrows--true north, grid north, and magnetic north--and the angles between them. Some maps, especially very old maps, do not have this diagram. True north, also called geodetic north or geographic north, is the direction of the line of longitude that bisects the quadrangle. All longitude lines converge to points at the north...

Satellites and ground-based magnetometers are both important for making measurements of the Earth’s magnetic field. They are not redundant but are instead complementary: Satellites provide good geographical coverage for data collection. Ground-based magnetometers are much less expensive and much easier to install than satellites. An array of magnetometers provides coverage from numerous locations...

The Earth's magnetic field does not directly affect human health. Humans evolved to live on this planet. High altitude pilots and astronauts can experience higher levels of radiation during magnetic storms, but the hazard is due to the radiation, not the magnetic field itself. Geomagnetism can also impact the electrically based technology that we rely on, but it does not impact people themselves...

Almost certainly not. Since the invention of the magnetometer in the 1830s, the average intensity of the magnetic field at the Earth's surface has decreased by about ten percent. We know from paleomagnetic records that the intensity of the magnetic field decreases by as much as ninety percent at the Earth's surface during a reversal. But those same paleomagnetic records also show that the field...

The Earth's outer core is in a state of turbulent convection as the result of radioactive heating and chemical differentiation. This sets up a process that is a bit like a naturally occurring electrical generator, where the convective kinetic energy is converted to electrical and magnetic energy. Basically, the motion of the electrically conducting iron in the presence of the Earth's magnetic...

Yes. There is evidence that some animals, like sea turtles and salmon, have the ability to sense the Earth's magnetic field (although probably not consciously) and to use this sense for navigation.

Although extremely unlikely, it might be possible for a reversal of the Earth's magnetic field to be triggered by a meteorite or comet impact, or even for it to be caused by something more "gentle," such as the melting of the polar ice caps. Self-contained dynamic systems like Earth’s dynamo can have reversals without any outside influence. Reversals of Earth's magnetic field can simply happen...

Yes. We can see evidence of magnetic polarity reversals by examining the geologic record. When lavas or sediments solidify, they often preserve a signature of the ambient magnetic field at the time of deposition. Incredible as it may seem, the magnetic field occasionally flips over! The geomagnetic poles are currently roughly coincident with the geographic poles, but occasionally the magnetic...