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Magnetic pole not coincident with rotational axis
In sci.astro message ,
Tue, 7 Jun 2011 16:19:12, Yousuf Khan posted: Even though the force has now been officially united and is called the Electromagnetic force, the magnetic part is a much more difficult force to analyse, as it acts in a rotational direction, while the electrical part acts radially. Prior to the 20th century, they were still considered separate forces, until the connection to electricity was found out. If you consider the 20th century to have started around 1825, yes. Read http://en.wikipedia.org/wiki/Magnetic_field. -- (c) John Stockton, near London. Web http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, and links. Correct = 4-line sig. separator as above, a line precisely "-- " (RFC5536/7) Do not Mail News to me. Before a reply, quote with "" or " " (RFC5536/7) |
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Magnetic pole not coincident with rotational axis
On Jun 6, 11:03*pm, Frisbieinstein wrote:
Why is the magnetic pole of many heavenly bodies not aligned with the axis of rotation? As best as I can tell no one really knows. *According to Wikipedia is is because of "non-dipole moments," Wikipedia has a slightly more detailed description. Here is a link to the Wikipedia article on dynamo theory. http://en.wikipedia.org/wiki/Dynamo_theory “In geophysics, dynamo theory proposes a mechanism by which a celestial body such as the Earth or a star generates a magnetic field. The theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales. History of theory In 1905, shortly after composing his special relativity paper, Albert Einstein described the origin of the Earth's magnetic field as being one of the great unsolved problems facing modern physicists.[citation needed] Since then, there have been many studies of the geodynamo problem based on historical measurements of the Earth's field. Walter Maurice Elsasser (March 20, 1904 - October 14,1991) was a German-born American physicist considered a "father" of the presently accepted dynamo theory as an explanation of the Earth's magnetism. He proposed that this magnetic field resulted from electric currents induced in the fluid outer core of the Earth. He revealed the history of the Earth's magnetic field through pioneering the study of the magnetic orientation of minerals in rocks. In order to maintain the magnetic field against ohmic decay (which would occur for the dipole field in 20,000 years) the outer core must be convecting. The convection is likely some combination of thermal and compositional convection. The mantle controls the rate at which heat is extracted from the core. Heat sources include gravitational energy released by the compression of the core, gravitational energy released by the rejection of light elements (probably sulphur, oxygen, or silicon) at the inner core boundary as it grows, latent heat of crystallization at the inner core boundary, and radioactivity of potassium, uranium and thorium.[1] At the dawn of the 21st century, numerical modeling of the Earth's magnetic field has not been successfully demonstrated, but appears to be in reach. Initial models are focused on field generation by convection in the planet's fluid outer core. It was possible to show the generation of a strong, Earth-like field when the model assumed a uniform core-surface temperature and exceptionally high viscosities for the core fluid. Computations which incorporated more realistic parameter values yielded magnetic fields that were less Earth-like, but also point the way to model refinements which may ultimately lead to an accurate analytic model. Slight variations in the core-surface temperature, in the range of a few millikelvins, result in significant increases in convective flow and produce more realistic magnetic fields.[2][3] Dynamo theory describes the process through which a rotating, convecting, and electrically conducting fluid acts to maintain a magnetic field. This theory is used to explain the presence of anomalously long-lived magnetic fields in astrophysical bodies. The conductive fluid in the geodynamo is liquid iron in the outer core, and in the solar dynamo is ionized gas at the tachocline. Dynamo theory of astrophysical bodies uses magnetohydrodynamic equations to investigate how the fluid can continuously regenerate the magnetic field. It was actually once believed that the dipole, which comprises much of the Earth's magnetic field and is misaligned along the rotation axis by 11.3 degrees, was caused by permanent magnetization of the materials in the earth. This means that dynamo theory was originally used to explain the Sun's magnetic field in its relationship with that of the Earth. However, this theory, which was initially proposed by Joseph Larmor in 1919,[4] has been modified due to extensive studies of magnetic secular variation, paleomagnetism (including polarity reversals), seismology, and the solar system's abundance of elements. Also, the application of the theories of Carl Friedrich Gauss to magnetic observations showed that Earth's magnetic field had an internal, rather than external, origin. There are three requisites for a dynamo to operate: An electrically conductive fluid medium Kinetic energy provided by planetary rotation An internal energy source to drive convective motions within the fluid. [5] In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core. A requirement for the induction of field is a rotating fluid. Rotation in the outer core is supplied by the Coriolis effect caused by the rotation of the Earth. The coriolis force tends to organize fluid motions and electric currents into columns (also see Taylor columns) aligned with the rotation axis. “ and even in the Earth and Sun the origin of the magnetic field is not understood ???????????????????????????? I listed some experimental studies in a separate post. |
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Magnetic pole not coincident with rotational axis
On Jun 8, 3:23*pm, "Mike Dworetsky"
wrote: There are still vigorous arguments over whether these fields are "fossil remnants" from the stellar collapse during formation, or generated by some sort of internal dynamo. *If the latter, it is strange that the strongest fields are found in the slowest rotators. In neutron stars the strongest fields are found with slow rotators. The reason is that some neutron stars form a dynamo, others do not. Those that form a dynamo have rotational energy transformed to the magnetic field, while the fast rotators have only the fossil field. I seem to recall that fast rotators tend to not form a dynamo because the speed of rotation exceeds the speed of convection. |
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Magnetic pole not coincident with rotational axis
On Jun 9, 5:41*am, Darwin123 wrote:
“and even in the Earth and Sun the origin of the magnetic field is not understood ???????????????????????????? I listed some experimental studies in a separate post. I should have written "not completely understood." According to my admittedly cursory search of the literature it is still not established in which layer of the sun the magnetic field is generated. |
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