Theory
Introduction
Almost everyone knows from childhood to aid orientation in nature - a compass. Not everyone asks the question, why is it that the needle goes just to the north. It is even possible that those who ask such a trivial question, with advancing technological development is declining. And yet it is one of the greatest mysteries of our planet, and not just its.
zdroj: http://stargazers.gsfc.nasa.gov/ resources/magnet_in_space.htm
Research on terrestrial magnetism brought valuable knowledge about the Earth and its evolution. The most complicated geomagnetic problem - the origin of the geomagnetic field - is solved by a number of leading research teams and has been largely elucidated, but can not say that would be resolved. It is a general consensus that the Earth's magnetism comes from the area of the Earth's core, which is inside the earth to a depth of 2900 km and an outer layer of the liquid according to the results of seismology. The liquid outer core layer enables the solid mantle and crust to be relatively rotated faster than the inner core. The electrons in the nucleus to the electrons because in the mantle and crust movement exercise. It is this movement of electrons forms a kind of natural dynamo and the result is similar to the magnetic field that causes electrical coil.
Compass needle points to the location somewhat remote from the geographic North and South Pole. The difference, known as declination, varies from place to place. Small variations in the Earth's magnetism is probably caused by small currents or eddies in the outer core, which formed upon contact with the core mantle. A large body of magnetic rocks and ores in the cortex may have a similar effect. Earth's magnetic field is distorted by electrically charged particles from the Sun. These particles flow in the upper atmosphere and the ground causing small fluctuations in the magnetic field. Some fluctuations are regular - e.g. day (night and day), some occasional - as magnetic storms.
The intensity of the magnetic field
The intensity of the magnetic field (magnetic induction) is expressed in units Tesla. The total intensity is around 50 μT. Important is also the direction of the geomagnetic field. Directed horizontally at the equator to the north, the north magnetic pole perpendicular to the Earth in the Czech Republic downwards towards the north. The total vector can be decomposed into individual components, as plotted in Figure 1
The vertical component Z is pointing down, the horizontal component H is heading to the north. The direction component H is slightly deviates from the geographical meridian, because the geomagnetic pole is not identical with the geographical pole. The angle between the direction of the H geomagnetic field and the geographical meridian is called the magnetic declination D. For example: in the Czech Republic, compass declination deviates by about 2.5° from the north-south direction to the northeast (with the apparent shift of the northern magnetic pole is about 6' to the east of the year).
The angle between the direction vector and the total horizontal component is called the magnetic inclination I and it is here around 65°.
Fig. 1 - Definition of components of the geomagnetic field.
Sometimes also used orthogonal components of the geomagnetic field, X (north) and Y (to the east), as are shown in Figure 1.
- Note:
- To illustrate the size of the individual components are not drawn to scale, is strongly increased and reduced component Y component Z.
History of measuring the Earth's magnetism
Effects of an unknown force on the magnet provoked the interest of scholars in antiquity. It is evident from such encyclopedic work "Naturalis historia" by C. Plinius, older, who lived in the 1st century after Christ. Besides, does the word "magnet" comes from ancient times: Magnetite was then called "lapis Magnes" the ancient city of Magnesia maloasijského, where his site.
In the Middle Ages phenomenon of magnetism sparked one of the first great works of experimental research, an essay entitled "Epistola Petri Peregrini de Maricourt ad Sygarum de Foucancourt, militem, de magnete". Petrus Peregrinus, who lived in the 13th century, was a French scholar and soldier. In his "Letter about the Magnet" was first defined the nature of the dipolar magnet, described the interaction between the poles and equipment that allow the use of the magnet. Refuted the idea that the magnetic compass needle is attracted to the mountains that supposedly exist somewhere in the north. Peregrina be considered the forerunner of the creators of modern scientific methodology.
William Gilbert
Another great scientist who studied the Earth's magnetism, William Gilbert was, an English doctor of Queen Elizabeth I. Written in 1600 and published a comprehensive monograph, whose long name begins with "De magnete". Although he had a quite small number of measurements the direction of the Earth's field, made the absolutely correct conclusion: the Earth's magnetic field is analogous to its spatial arrangement of the ball field, magnetite, and therefore: Earth itself is a big magnet.
Edmond Halley
Earth's magnetism is discussed also known astronomer Edmond Halley. He organized two research cruises crisscrossing the Atlantic Ocean to explore in detail, how do we change the direction of the magnetic needle. In his days, it was long known that the compass does not point exactly to the north and that its deviation from the northern direction (magnetic declination) changes from place to place. Halley recognized that some elements of Earth's magnetism with time shifting to the west, and of which with remarkable prescience concluded that the Earth has a "core", which is the bearer of magnetism, and that this core is in arrears in rotation of the outer layer of the Earth. Their findings published in 1698, but was then met with positive response. Today it is clear that his ideas were very close to the truth.
Carl Friedrich Gauss
The knowledge of the geomagnetic field has contributed substantially famous mathematician and physicist Carl Friedrich Gauss. Prepared by a mathematical procedure which allows to calculate the geomagnetic vector at any point on Earth or above it, if we have a finite number of measurements (Alexander von Humboldt brought Gauss geomagnetic field measured values from different regions of the world, when Humboldt studied the earth's magnetism on their science research vessels). Gaussian process can also tell whether the geomagnetic field is energized only within the country or even beyond. This work was published in 1839 by Gauss in his book "Allgemeine therie des Erdmagnetismus" (General Theory of the Earth's magnetism).
Gaussian process showed that the bulk of the geomagnetic field (about 90 %) is, as if it attracted the elementary magnetic dipole. This term we can bring a little inaccurate idea of bar magnet. Dipole is located approximately in the center of the Earth and its axis forms a small angle (currently it is about 11°). Gilbert's statement that the Earth itself is a magnet reached this mathematical confirmation.
