George Mallory, English mountaineer, exclaimed “because it is there” in response to a question why he wants to climb Mount Everest. This is the most obvious and simplistic answer.
Why do we need to study geomagnetism, can also elicit the same innocent response. I can recite thousands of ‘academic’ and ‘practical’ reasons though. The scientists, operative in the arena of geomagnetism, have written a huge number of tomes. They take this field very seriously!
But, for a common person, is it really necessary to go into the nitty-gritty of geomagnetism? It is not. It is not a matter of life and death for a person to not ‘know’ geomagnetism.
In any case, in a life and death matter, like if one is afflicted with life threatening disease, it is the doctor that we go to. We do not try to cure such terminal health issues on our own. The experts do it for us. However, we do take basic information to tide over the situation.
It is not necessary that all of us understand geomagnetism in all its complex entirety. We need to have, however, experts that can keep a close watch on it and educate us on why we need to study geomagnetism.
Science has advanced manifold from rudimentary to complex. It has evolved over hundreds of years. In the starting phase of ‘science’ the repeatability or cyclicity of seasons was recognized that led to the ‘why’ and ‘how’.
The same manner of phase played out in geomagnetism. Once the ancients realized the affinity of certain mineral (magnetite) towards metal, their curiosity was aroused. It led them to understand the ‘magnetized’ needle always pointed to a certain direction (we began to call it north), which changed with time.
The geographic north is fixed. But, the magnetic north keeps moving, either to the east or west of this geographic north. The magnetoelectric currents generated through sun’s influence, and the convection currents inside the earth are responsible for the changing position of poles.
In ancient times, when the compass became an essential tool to navigate from one place to another, the changing of ‘north’ became a matter of life and death for many. Especially for those who glided over the oceanic waters devoid of any visual clue. Many perished, while some ‘discovered’ new land because the magnetic field had imperceptibly changed ‘direction’.
The angle between geographic north and magnetic north is called as declination.
The geographic north is specified by North Star or the Pole Star. Draw an imaginary line straight down the star and if you are to the left of this line you are having ‘west’ declination. To the right will be ‘east’ declination. The declination shown in the figure is ~150East. D in Mumbai is 0029’5” W and Delhi it is 0055’17” E (as on June 2018). Very rarely the magnetic and geographic north can coincide with each other, in which case the declination will be zero.