Introduction:
"Chidambaram Natarajar temple is not likely to be the
Centre Point of world’s Magnetic Equator", says Arumugham Natarajan of Ponnamaravathi Pudupatti, Pudukkottai district of Tamilnadu.
The
myth:
There is a myth and rumour that Chidambaram
Natarajar temple of Tamilnadu, India is located at the Centre Point of world’s
Magnetic Equator.
The dance of Lord Nataraja is described as Cosmic
Dance by Western Scientists.
R & D Western scientists have proved that in Chidambaram,
at Lord Nataraja’s big toe is the Centre Point of World’s Magnetic Equator.
Ancient Tamil Scholar Thirumoolar has proved it five
thousand years ago! His treatise Thirumandiram is a wonderful scientific guide
for the whole world.
Chidambaram, Tamil Nadu, India is the Geo Magnetic
Centre of the Earth/Universe and the centre of Geo magnetic equator.
Explanation:
This rumour is spread without proper references.
In fact, the Earth's geographic equator is an
imaginary line. It doesn’t change its position. However, the magnetic equator
is not fixed. It changes slowly.
Magnetic
Equator:
Magnetic dip results from the tendency of a magnet
to align itself with lines of force. As the Earth’s magnetic lines of force are
not parallel to the surface, the north end of a compass needle will point
downwards in the northern hemisphere (positive dip) or upward in the southern
hemisphere (negative dip). The range of dip is from −90 degrees (at the South
Magnetic Pole) to +90 degrees (at the North Magnetic Pole). Contour lines along
which the dip measured at the Earth’s surface is equal are referred to as
isoclinic lines. The locus of the points having zero dip is called the magnetic
equator or aclinic line.’
Definition
of aclinic line: an imaginary line on the earth's
surface roughly parallel to the geographical equator and passing through those
points where a magnetic needle if suspended freely has no dip or inclination
and assumes a horizontal position— called also magnetic equator.
The
Earth's magnetic field:
The Earth acts like a large spherical magnet: it is
surrounded by a magnetic field that changes with time and location. The field
is generated by a dipole magnet (i.e., a straight magnet with a North and South
Pole) located at the centre of the Earth. The axis of the dipole is offset from
the axis of the Earth's rotation by approximately 11 degrees. This means that
the north and south geographic poles and the north and south magnetic poles are
not located in the same place. At any point and time, the Earth's magnetic
field is characterized by a direction and intensity which can be measured.
Often the parameters measured are the magnetic declination, D, the horizontal
intensity, H, and the vertical intensity, Z. From these elements, all other
parameters of the magnetic field can be calculated.
The
Main Field:
The geomagnetic field measured at any point on the
Earth's surface is a combination of several magnetic fields generated by
various sources. These fields are superimposed on and interact with each other.
More than 90% of the field measured is generated INTERNAL to the planet in the
Earth's outer core. This portion of the geomagnetic field is often referred to
as the Main Field.
The Main Field varies slowly in time and can be
described by mathematical models such as the International Geomagnetic
Reference Field (IGRF) and World Magnetic Model (WMM). The Earth's Main Field
dominates over the interplanetary magnetic field in the area called the
magnetosphere.
The magnetosphere is shaped somewhat like a comet in
response to the dynamic pressure of the solar wind. It is compressed on the
side towards the sun to about 10 Earth radii and is extended tail-like on the
side away from the sun to more than 100 Earth radii. The magnetosphere deflects
the flow of most solar wind particles around the Earth, while the geomagnetic
field lines guide charged particle motion within the magnetosphere. The
differential flow of ions and electrons inside the magnetosphere and in the
ionosphere form current systems, which cause variations in the intensity of the
Earth's magnetic field. These EXTERNAL currents in the ionized upper atmosphere
and magnetosphere vary on a much shorter time scale than the INTERNAL Main
Field and may create magnetic fields as large as 10% of the Main Field.
The
magnetic elements:
To measure the Earth's magnetism in any place, we
must measure the direction and intensity of the field. The Earth's magnetic
field is described by seven parameters. These are declination (D), inclination
(I), horizontal intensity (H), the north (X) and east (Y) components of the
horizontal intensity, vertical intensity (Z), and total intensity (F). The
parameters describing the direction of the magnetic field are declination (D)
and inclination (I). D and I are measured in units of degrees, positive east
for D and positive down for I. The intensity of the total field (F) is
described by the horizontal component (H), vertical component (Z), and the
north (X) and east (Y) components of the horizontal intensity. These components
may be measured in units of gauss but are generally reported in nanoTesla (1nT
* 100,000 = 1 gauss). The Earth's magnetic field intensity is roughly between
25,000 - 65,000 nT (.25 - .65 gauss). Magnetic declination is the angle between
magnetic north and true north. D is considered positive when the angle measured
is east of true north and negative when west. Magnetic inclination is the angle
between the horizontal plane and the total field vector, measured positive into
Earth. In older literature, the term “magnetic elements” often referred to D,
I, and H.
The
magnetic field changes in different locations:
The magnetic field is different in different places.
In fact, the magnetic field changes with both location and time. It is so
irregular that it must be measured in many places to get a satisfactory picture
of its distribution. This is done using satellites, and approximately 200
operating magnetic observatories worldwide, as well as several more temporary
sites. However, there are some regular features of the magnetic field. At the
magnetic poles, a dip needle stands vertical (dip=90 degrees), the horizontal
intensity is zero, and a compass does not show direction (D is undefined). At
the north magnetic pole, the north end of the dip needle is down; at the south
magnetic pole, the north end is up. At the magnetic equator the dip or
inclination is zero. Unlike the Earth's geographic equator, the magnetic
equator is not fixed, but slowly changes.
Magnetic
pole:
The magnetic poles are defined as the area where dip
(I) is vertical. You can compute this area using magnetic field models, such as
the World Magnetic Model (WMM) and the International Geomagnetic Reference
Field (IGRF). You can also survey for the magnetic pole, using instruments that
measure the magnetic field strength and direction. In practice, the geomagnetic
field is not exactly vertical at these poles, but is vertical on oval-shaped
loci traced on a daily basis, with considerable variation from one day to
another, and approximately centred on the dip pole positions. Magnetic
declination (D) is unreliable near the poles.
Magnetic
equator:
The magnetic equator is where the dip or inclination
(I) is zero. There is no vertical (Z) component to the magnetic field. The
magnetic equator is not fixed, but slowly changes. North of the magnetic
equator, the north end of the dip needle dips below the horizontal, I and Z are
positive. South of the magnetic equator, the south end dips below the
horizontal, I and Z are measured negative. As you move away from the magnetic
equator, I and Z increase.
The
Earth's magnetic field has changed significantly in the last several years:
The Earth's magnetic field is slowly changing and
appears to have been changing throughout its existence. When the tectonic
plates form along the oceanic ridges, the magnetic field that exists is
imprinted on the rock as they cool below about 700 Centigrade. The slowly
moving plates act as a kind of tape recorder leaving information about the
strength and direction of past magnetic fields. By sampling these rocks and
using radiometric dating techniques it has been possible to reconstruct the
history of the Earth's magnetic field for the last 160 million years or so.
Older “paleomagnetic” data exists but the picture is
less continuous. An interlocking body of evidence, from many locations and
times, give paleomagnetists confidence that these data are revealing a correct
picture of the nature of the magnetic field and the Earth's plate motions. In
addition, if one “plays this tape backwards” the continents, which ride on the
tectonic plates, reassemble along their edges with near perfect fits. These
“reassembled continents” have matching fossil floras and faunas. The picture
that emerges from the paleomagnetic record shows the Earth's magnetic field
strengthening, weakening and often changing polarity (North and South magnetic
poles reversing).
Earth's
magnetic field is going to reverse:
While we now appear to be in a period of declining
magnetic field strength, we cannot state for certain if or when a magnetic
reversal will occur. Based on measurements of the Earth's magnetic field taken
since about 1850 some paleomagnetists estimate that the dipole moment will
decay in about 1,300 years. However, the present dipole moment (a measure of
how strong the magnetic field is) is actually higher than it has been for most
of the last 50,000 years and the current decline could reverse at any time.
Even if Earth's magnetic field is beginning a reversal, it would still take
several thousand years to complete a reversal. We expect Earth would still have
a magnetic field during a reversal, but it would be weaker than normal with
multiple magnetic poles. Radio communication would deteriorate, navigation by
magnetic compass would be difficult and migratory animals might have problems.
During the past 100 million years, the reversal
rates vary considerably. Consecutive reversals were spaced 5 thousand years to
50 million years. The last time the magnetic field reversed was about 750,000 -
780,000 years ago. While we now appear to be in a period of declining magnetic
field strength, we cannot state for certain if or when a magnetic reversal will
occur. Based on measurements of the Earth's magnetic field taken since about 1850
some paleomagnetists estimate that the dipole moment will decay in about 1,300
years. However, the present dipole moment (a measure of how strong the magnetic
field is) is actually higher than it has been for most of the last 50,000 years
and the current decline could reverse at any time.
A
reversal of the magnetic field will affect animal behaviour:
Many migratory animals use the geomagnetic field to
orient themselves. However, the mechanism underlying this ability of animals
remains unknown. Experiments show that migratory birds can sense the
declination and inclination of the local geomagnetic field. Changing the
polarity of the horizontal magnetic field is known to affect the hanging
position of bats. Some migrating butterflies use the geomagnetic field for
direction. In the ocean, spiny lobsters, dolphins, and whales are known to use
geomagnetic field for directions. It is thus, possible that a reversal of
geomagnetic field affect the migratory behaviour of some animals. Since the
chance of a reversal in the near future (in the next few hundred years) is very
low, no immediate concern is required.
Conclusion:
It can be concluded that Chidambaram Natarajar
temple is not likely to be the Centre Point of world’s Magnetic Equator.
