Gauss, Carl Friedrich
German mathematician
(1777 - 1855), in the beginning of the 19th
century known for his works in physics and mathematics. He did for the
first time an absolute measurement of the intensity of the geomagnetic
field and a global analysis of the geomagnetic field, called
spherical
harmonical analysis. He is also known for the law of Gauss, which
allows to define an error at a given level of confidence for the
estimation of the true mean of a series of observations.
Geographic meridial
plane
Plane containing the local vertical and the rotation axis of the Earth.
Geographic north/south
pole
Point on the surface of the Earth in the northern/southern hemisphere,
situated on the Earths rotation axis. Follow this link
to see the definitions of the geographic and the geomagnetic coordinate
system.
Geomagnetic field
Magnetic field of the
Earth. Resembles the field of a centric magnetic
dipole inclined about 11.4° to the rotation axis of the Earth.
It
is defined in each place at a certain instant of time by its direction
(declination, inclination) and intensity. The geomagnetic
field is divided in an internal part (the
main part), which is caused by fluid movements in the outer fluid core
of the Earth and other sources in the upper Earth mantle and the
Earth’s crust, and an external part which is caused by currents in the
ionosphere and magnetosphere. A complete mathematical description of
the potential of the total magnetic field was developed by C.F.
Gauss based on spherical
harmonics.
Geomagnetic north/south pole
Poles based on a global analysis of the observed geomagnetic
field
limited to dipole terms. The
geomagnetic poles corresponding to the
International Geomagnetic
Reference Model (IGRF) of 2005 are situated
at:
North
geomagnetic pole: 79.7° N and 71.8° W
South
geomagnetic pole: 79.7° S and 108.2°E
Follow this link
to see the definitions of the geographic and the geomagnetic coordinate
system.
Geomagnetic reversal
The phenomenon of
polarity change of the geomagnetic field. Currently, the south magnetic pole is
situated in the southern hemisphere and the north magnetic pole in the northern
hemisphere (normal polarity). This was not always the case in the
Earth's past. If the magnetic poles are oppositely situated compared to
now (i.e. the magnetic north pole was in the southern hemisphere) one
speaks about reversed polarity. Such polarity switching occurred many
times in the geological past. The time between geomagnetic reversals is
termed chron. We are presently in the Brunhes chron, called after
Bernhard
Brunhes (1867-1910). The chron before, when the magnetic poles were oppositely situated
compared to now, is called Matuyama, named after Motonori Matuyama
(1884-1958). The last geomagnetic reversal, known with certainty,
occurred 778 000 years ago
and is called Matuyama/Brunhes.
Goethite
Antiferromagnetic
mineral, but exhibits a weak ferromagnetic moment due to defects in
the
crystal structure. Acicular or fibrous, but in general isometric and of
irregular form. Colour: brown-black, yellowish brown to red. In powder
form yellow-brown to yellow-orange colour. Metallic to ashy
reflectance. Hardness 5 to 5.5. Very common as alteration product in
certain soils and sediments. Remains stable in recent soils of the
temperate and humid climate zones, but can be transformed into
fine-grained Haematite with time. Identified in 1806 as a new mineral
named in honour of the German poet Johann Wolfgang von Goethe, also a
great collector of minerals.
Grain
A macroscopic sample
of a crystalline mineral will generally
consist of multiple conjoined crystals of varying shapes and sizes.
Each of these crystals, within which the atoms are arranged on a single
regular lattice, is termed grain