The magnetism of the earth is more important than many believe.
The magnetism
We are all familiar with the magnetism, either in minor or to a greater extent. One of the most common ways in which this physical phenomenon manifests itself, or one of the most accustomed we are to witness in everyday life, is the ability of certain objects to attract or repel other metals. Sure, I mean the magnets, present in all kinds of objects that we use every day
The first steps of magnetism
The first magnetic phenomena observed were undoubtedly those related to the so-called natural magnets, which are pieces of an iron ore found next to the ancient city of Magnesia called magnetite (Fe3O4), or magnet stone.
The ancient Greeks realized that these magnets attracted small pieces of iron. In 1269 Petrus Peregrinus de Maricourt, wrote to a friend, where he gave a clear description of the magnetic compass, which had developed during the eleventh and twelfth centuries probably in China.
De Maricourt observed that the magnet stones of spherical shapes had two special points called "poles" which he located depositing iron filings on them. The lines drawn along the filing intersected at two points which I call the north pole and the south pole. He also found that equal poles repel each other and different poles attract each other. These ideas were incorporated into the work of the English William Gilbert (1544-1603) who is known as the father of magnetism, he in 1600 published the results of his own observations in his work De Magnete, where he described the behavior of a needle magnetic field near another magnet and clearly established the differences and similarities between the electric and magnetic forces. He was the first to realize that the earth behaves like a magnet, explaining why the compass points to the north.
For many years the study of magnetic phenomena focused on permanent magnets. By the beginning of the nineteenth century, a large amount of experimental information had accumulated about the nature of electricity and magnetism. The discoveries and ideas of Gilbert, Franklin, Coulomb, Volta and many others were well known.
The similarities between electric and magnetic attraction, the repeated observation of the compass behavior of ships that were struck by lightning, sometimes their needle changed its polarity and other experiments such as Franklin's magnetization of needles passing between them electric shock, all pointed to a possible connection between electrical and magnetic behavior. But until early 1819, magnetism and electricity were considered as two independent phenomena. In that year, the Danish physicist Hans Christian Oesterd (1777-1851) observed that a magnet deviates when being in the proximity of a conductive thread that carries a current. Soon after, the French physicist André Ampère (1775-1836) formulated quantitative laws to calculate the magnetic force between conductors through which electric currents circulate. He also suggested that molecular-sized electric current loops are responsible for all magnetic phenomena.
In the 1820s, additional connections between electricity and magnetism were demonstrated by the English physicist Michael Faraday (1791-1867) and the North American physicist Joseph Henry (1797-1878). The two independently showed that an electric current can be produced in a circuit either by moving a magnet near the circuit or by changing the current in another nearby circuit. These observations showed that a magnetic field produces an electric field.
Electrons and magnetic fields
The electron is a particle that is part of the atomic structure and functions as a small magnet. The electrons are oriented in different directions, but in a magnet they are oriented towards a common direction, which attracts objects with an opposite pole. Thus, a body with electrons oriented in one X direction will be attracted to another oriented to a Y direction, generating a magnetic field between them and thus call magnetic field to the area of influence exerted by the magnetic force. But, on the other hand, if two objects with electrons facing the X direction come together, they repel and can not join. The force (intensity or current) of a magnetic field is measured in Gauss (G) or Tesla (T). The flow decreases with the distance to the source that the field causes.
Magnetic Field Lines
The lines of the magnetic field similarly describe the structure of the magnetic field in three dimensions. They are defined as follows. If at any point of that line we place an ideal compass needle, free to rotate in any direction, the needle will always point along the field line (bottom drawing).
The field lines converge where the magnetic force is greatest and they separate where it is weakest. For example, in a compact magnetic bar or "dipole", the field lines are separated from one pole and converge in the other and the magnetic force is greater near the poles where they meet. The behavior of the lines in the earth's magnetic field is very similar.
The field lines were introduced by Michael Faraday, who called them "lines of force". For many years they were seen merely as a way of visualizing magnetic fields and electrical engineers preferred other, more mathematically useful ways. However, it was not like that in space, where the lines were fundamental to the way electrons and ions moved. These electrically charged particles tend to remain attached to the field lines where they settle, spiraling around them as they slide through them, like beads on a necklace (bottom drawing).
(https://giphy.com/search/electron)
The magnets
A magnet is a body or device with a significant magnetism, so that it attracts other magnets and / or ferromagnetic metals (for example, iron, cobalt, nickel and these alloys). It can be natural or artificial. Natural magnets maintain their continuous magnetic field, unless they suffer a large blow or are subjected to opposite magnetic charges or high temperatures (above the Curie Temperature).
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Earth as a magnet
The Earth behaves like a huge magnet. The English physicist and natural philosopher William Gilbert was the first to point out this similarity in 1600, although the effects of terrestrial magnetism had been used much earlier on primitive compasses.
The magnetism of the Earth is the result of a dynamic, since its iron core of the Earth is not solid.
On the other hand, in the terrestrial surface and in the atmosphere diverse electrical currents produced by diverse causes are generated, in addition to a constant exchange of electricity between the air and the Earth.
Our planet creates its own magnetic field thanks to the electric currents that are created by the liquid nickel-iron nucleus, and as we said before the Earth is like a gigantic magnet with two poles: a North pole and a South pole; although, as you know, these magnetic poles are not aligned with the geographical poles. The difference are:
• Geographical North Pole: it is defined by latitude 90º and is the axis by which the Earth makes the rotation movement.
• Magnetic North Pole: this pole is where the Earth's magnetic field points vertically downward.
• Magnetic South Pole: is located near the Adélie coast, in Antarctica, about 2600 kilometers from the Geographic South Pole.
For example, the compass needles are guided in the direction of magnetic field lines, which are different from those of the Geographic North Pole as we saw earlier. Something curious that has to do with the compass system is that the needle is magnetized with the northern tip painted red, and is attracted by the north magnetic pole; so if we speak purely of the magnetic, the north magnetic pole is a south pole that attracts the needles. We call it "north pole" simply because it is close to the geographic north.
Origin of the Earth's magnetic field
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The terrestrial magnetic field originated with the movements of liquid metals in the planet's core. This field extends from the nucleus, progressively attenuating itself in outer space.
In turn, it causes electromagnetic effects in the magnetosphere and protects us from the solar wind. In addition, it also allows very diverse phenomena, such as the orientation of the rocks at the oceanic ridges, the magneto-perception of some animals and the orientation of people using compasses.
As we know, a magnetic field is produced with the movement of electric charges, as happens, for example, in a magnet: where it occurs when electrons move with negative charge. The true origin of the Earth's magnetic field has not yet been fully understood, but we are sure of some things, in large part, thanks to Elsasser.
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The components of the Earth Magnetic Field.
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The terrestrial magnetic field is a vectorial magnitude and as such it is characterized by its module, its direction and its sense. The module of this vector is called total force or total intensity, F. Equivalent to the vector module resulting from the vector sum of its three Cartesian components (X, Y, Z).
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The composition of X and Y gives rise to the horizontal component, H.
The angle that forms H with the X axis (direction of the Geographic North) is called "Declination", D.
The angle that forms H with the Z axis is called "Tilt", I.
The unit of measurement of the total intensity of the geomagnetic field F and its components is called Tesla (T). This unit is too large for the CMT measurement. Therefore a submultiple is used, the nanotesla, nT (1nT = 10-9 Tesla).
The magnitude of F is of the order of 30,000 nT in Ecuador and 60,000 nT in the Poles, with its direction practically horizontal in Ecuador and vertical in the Poles.
What is the value of the earth's magnetic field?
Its magnitude on the surface of the Earth varies from 25 to 65 μT (microteslas) or (0.25-0.65 G). The field created by a dipolomagnetic can be considered in approximation inclined an angle of 15 degrees with respect to the axis of rotation (like a bar magnet).
Main characteristics of the terrestrial magnetic field.
Description
Most commonly used coordinate systems to represent the earth's magnetic field.
The magnetic field can be represented at any point by a three-dimensional vector. A common way to measure your direction is to use a compass to determine the magnetic north direction. Its angle with respect to geographic north is called declination. Pointing towards magnetic north the angle that the field maintains with the horizontal is the inclination. The intensity (F) of the field is proportional to the force exerted on the magnet. You can also use a representation with XYZ coordinates in which the X is the direction of the parallels (with east direction), the Y is the meridian direction (towards the geographic north pole) and the Z is the vertical direction (with the downward sense pointing to the center of the Earth).
Intensity
The field strength is maximum near the poles and minimum close to the equator. It is measured with some frequency in Gauss (one ten thousandth of Tesla), but it is usually represented using the nanoteslas (nT), being 1 G = 100 000 nT. The nanotesla is also called a gamma) .101112 The field varies between approximately 25,000 and 65,000 nT (0.25-0.65 G). In comparison the magnet of a refrigerator has a field of 100 gauss.
Intensity of the Earth's magnetic field taken from the World Magnetic Model (World Magnetic Model or WMM) for 2010.
The isoline maps of intensity are called isodynamic charts. In the image on the left you can see an isodynamic chart of the Earth's magnetic field. The minimum intensity occurs over South America, while the maximum occurs over northern Canada, Siberia and the Antarctic coast south of the Australian continent.
Tilt
Inclination of the Earth's magnetic field from WMM data for 2010.
The inclination is given by the angle by which the field points downwards with respect to the horizontal. It can have values between -90º (upwards) and 90º (downwards). At the north magnetic pole, it points completely downwards, and progressively rotates upwards as the latitude decreases to the horizontal (0º inclination), which is reached at the magnetic equator. Continue rotating until you reach the vertical at the magnetic south pole. The inclination can be measured with a tilt circle.
An isoline map of the Earth's tilt is shown in the figure to the right.
Declension
The declination is positive for a deviation of the field towards the east relative to the geographic north. It can be estimated by comparing the orientation of a compass with the position of the celestial pole. The maps usually include declination information as a small diagram showing the relationship between magnetic and geographic north. The information of the declination for a region can be represented by an isogonic chart (map of isolines that join points with the same declination).
Declination of the Earth's magnetic field from the WMM of 2010. The isogonic lines offer the declination in degrees.
An isogonic chart of the Earth's magnetic field is shown in the image on the left.
Dipolar approximation.
Near the Earth's surface, the Earth's magnetic field can be reasonably approximated by that created by a magnetic dipole located at the center of the Earth and inclined at an angle of 11.5 degrees to the planet's axis of rotation. The dipole is approximatable to a bar magnet, with the south pole pointing towards the geomagnetic north pole. This might seem surprising, but the north pole of a magnet is defined by the attraction to the north pole of the Earth. On the basis that the north pole of a magnet attracts the south pole of other magnets and repels the north poles, it must be attracted to the south pole of the Earth magnet. This dipolar field accounts for about 80-90% of the total field in most locations.
Magnetic poles
The movement of the magnetic north pole of the Earth along the Canadian Arctic.
The position of the magnetic poles can be defined in at least two ways. A magnetic tilt pole is a point on the earth's surface in which its magnetic field is fully vertical.
The inclination of the Earth's field is 90º at the magnetic north pole and -90º at the magnetic south pole. The two poles move independently of each other and are not located perfectly opposite at opposite points of the globe. Its displacement can be rapid: movements of the magnetic north pole have been detected above 40 km per year. Over the past 180 years, the magnetic north pole has been migrating northwestward, from Cape Adelaide on the Boothia peninsula in 1831 to Resolute Bay 600 km away in 2001. The magnetic equator is the zero-level curve (the magnetic field is horizontal).
If a line is drawn parallel to the moment of the dipole that comes closest to the Earth's magnetic field, the points of intersection with the Earth's surface are called the geomagnetic poles. That is, the north and south geomagnetic poles would be equivalent to the north and south magnetic poles if the Earth were a perfect dipole. However, the Earth's field presents a significant contribution of non-dipolar terms, so the poles do not coincide.
Importance of the magnetic field
The Earth is mostly protected from the solar wind, a flow of charged energetic particles emanating from the Sun, due to its magnetic field, which diverts most of the charged particles. These particles would destroy the ozone layer, which protects the Earth from harmful ultraviolet rays. The calculation of the carbon dioxide loss from the atmosphere of Mars - which resulted in the capture of ions from the solar wind - is consistent with the loss almost total of its atmosphere consequence of the extinction of the magnetic field of the planet.
The polarity of the Earth's magnetic field is recorded in sedimentary rocks. The inversions are detectable as bands centered on the ocean ridges in which the oceanic bed expands, while the stability of the geomagnetic poles between the different investment events allows the paleomagnetists to follow the drift of continents. The investments also constitute the the basis of magnetostratigraphy, a method of dating rocks and sediments. The field also magnetizes the crust; anomalies can be used to detect valuable ore ores.
Humans have used compasses to orient themselves since the 11th century BC. C., and for navigation since the twelfth century.
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