Earth’s Magnetic Fields – How Do Magnets Work?
You must have noticed that when a magnet is freely suspended, it always points in the North-South direction even when there is no other magnet. This indicates that the Earth itself works as a magnet and compels any freely suspended magnet (or magnetic needle) to point in a particular direction: North and South. Note that the real shape of the Earth’s magnetic field looks like a bar magnet of length one-fifth of the Earth’s diameter buried at its center. The South Pole of the Earth’s magnet is known as the geographical North as it always attracts the North Pole of the suspended magnet and vice versa. Therefore, there is always a magnetic N-pole near the geographical South and a magnetic S-pole near the geographical North. Also, when it comes to the position of the Earth’s magnetic poles, they are not well-defined on the globe and are spread over an area. Even the axis of Earth’s magnet and the geographical axis do not coincide. The axis of the Earth’s magnetic field is inclined at an angle of about 15o with the geographical axis. Because of this, any freely suspended magnet forms an angle of about 15o with the geographical axis and points roughly in the North-South directions at a place only. Simply put, a freely suspended magnet never shows the exact geographical South and North as the magnetic axis and geographical axis of the Earth do not coincide. In this article, read more about Earth’s magnetic field, magnetic meridian and more!
The Reason behind Earth’s Magnetism
Geophysicists believe that the Earth’s magnetism happens because of the magnetic effect of a current that is flowing in the liquid core at the center of the Earth. So, it can be said that the Earth is a huge electromagnet.
The Earth is made up of a solid iron core. That iron core is surrounded by an ocean of hot, liquid metal. This liquid metal which flows in Earth’s core produces electrical currents, which in turn creates our magnetic field.
Also, the liquid metal surrounding the inner core moves freely unlike a solid fridge magnet. This more or less explains the reason why the magnetic pole can migrate.
Even though geophysicists cannot determine the inner core directly, there is a strong belief that the matter which governs the Earth’s magnetic field moves around.
Elements of the Earth’s Magnetic Field
For understanding the Earth’s magnetic field at any place, it’s crucial to know the following two quantities or elements:
- Declination
- Angle of Dip (or Inclination)
Declination
The magnetic meridian is an important concept for understanding the Earth’s magnetic field. Magnetic meridian is nothing but the vertical plane which passes through the axis of a freely suspended magnet. The direction of Earth’s magnetic field may not be horizontal and lies in the magnetic meridian. The vertical plane that passes through the true geographical North and South (or geographical axis of Earth) is known as the geographical meridian. The angle between the magnetic meridian and the geographic meridian at a place is called declination at that place.
Note that actual value of the angle of declination keeps changing at different places on Earth. We should know the angle of declination at that place for finding out the exact geographic directions (North and South) at a place by using a magnetic compass. The declination is expressed in degrees East (o E) or degrees West (o W). For instance, a declination of 2 o E implies that the compass would be pointing 2 degrees east of true geographical North. Therefore, knowing the declination at a place does help in finding the true geographical directions at that place. In all the maps used by surveyors, air pilots and mariners, the declination for different places is always indicated. Also, at the places of zero declination, the compass North will coincide with the true geographical North.
Angle of Dip or Inclination
By now, we have only talked about one type of magnetic needle that can move in the horizontal place and points approximately in the North-South direction. Now, what if we consider a magnetic needle that is free to rotate in the vertical plane? Then, in this case, it will not remain perfectly horizontal. The compass needle creates a definite angle with the horizontal direction. In fact, the North Pole of the magnetic needle dips below the horizontal line in the Northern Hemisphere of Earth. At any given place, the magnetic needle will always point in the direction of the resultant intensity of Earth’s magnetic field at the place.
Angle of Dip at the Poles
The magnetic lines of force at the poles of Earth remain vertical because of which the magnetic needle becomes vertical. The angle of dip at the magnetic poles of Earth is 90 o.
Angle of Dip at the Equator
All the lines of force surrounding the magnetic equator of the Earth are completely horizontal. So, the magnetic needle automatically becomes horizontal there. Therefore, the angle of dip at the magnetic equator of the Earth will be 0 o. Please note that the angle of dip keeps varying from place to place.
Polar Shift Theory: Earth’s Ever-Changing Magnetic North Pole
We all know that the world is in a dynamic state and the earth is changing every day.
Continents are pushed apart by plate tectonics, the sea levels fluctuate up and down; volcanoes erupt and create ash and smoke.
All these examples are of natural phenomena, and they keep happening in cycles and are dynamic on our planet. The location of our magnetic north is also not different.
Did you know that the magnetic pole has crept north over 1000 kilometres over the last 150 years? Amazing, right? Scientists believe that it migrates about 10 kilometres every year and can even completely flip from pole-to-pole. But now, the speed has increased to around 40 kilometres per year and can also reach Siberia in a few decades.
NOAA’s historical declination map shows lines of constant magnetic declination (isogonic lines). Isogonic lines indicate in what direction compass needles will point – along the lines of magnetic force.
Concept of Polar Reversals: South-Pole Pointing Compass
Just imagine that your compass starts pointing south instead of north.
If we would have been alive to witness it 800,000 years ago, then it would have been the Magnetic South Pole.
For the earth’s magnetic field to flip polarity, it takes a staggering 200,000 to 300,000 years. When the polarity flips, the lines of attraction that enter the Earth also flip north to south pole, or vice versa.
This indicates that it has been twice that long since the last reversal. Many scientists believe that we are long overdue for a pole reversal. But there’s no reason to panic as NASA scientists have stated that the reversal happens over hundreds or thousands of years. So, it is not precisely a perfect back flip that happens like a flick of a switch.
This was our article about the earth’s Magnetic Meridian. For more such articles, keep following us here!
