The Earth and magnetism
The Earth behaves as though it is a large magnet with poles at each
end of the axis. At one time it was thought that there was a real magnet
inside the Earth, but this is now known not to be the case.
Why does the Earth
have a magnetic field?
Magnetic fields are generated by moving electrical charges. While
the source of Earth's magnetic field is still under study, it's generally
believed that it arises from motion within the Earth's outer core, which
contains molten iron.
Magnets you use in everyday life have two poles - named the North pole
and the South pole. The Earth's magnetic field has poles too. The Earth's
magnetic field is tipped in relation to its geographic poles. The field
is rather complicated, and there are different possible definitions
for the magnetic poles.
A simple magnetic field that best approximates to the Earth's field
is tilted at about 11° to the Earth's rotational axis. The North
and South magnetic poles are most often referred to as the two points
on the Earth's surface where the Earth's magnetic field points straight
up and down. They are presently located at about 107°W, 80°N
(in the Arctic Ocean north of Canada), and at about 139°E, 64.5°S
(off the coast of Antarctica).
They also drift. The South Magnetic Pole is currently moving Northwest
at about 5 kilometres every year, while the North Magnetic Pole is also
moving Northwest, but at about 20 kilometres a year.
Magnetic records in rock samples show not only that the poles move,
but many times in the past they have even been totally reversed! That
is the North and South poles have swapped places. Since this has not
been experienced in modern times, we do not know how this happens or
what happens during pole reversal.
Magnetic storms
Earth's magnetic field can be disturbed, particularly by electrically
charged particles from the Sun. The Sun continually sends out charged
particles in the form of bits of atoms known as the solar wind. Sometimes
this wind becomes very strong and creates a great interference with
Earth's magnetic field known as a magnetic storm. One effect of these
magnetic storms is to disrupt radio communication, especially where
the radio signal is bounced from the ionosphere to travel around the
Earth's curved surface.
Another spectacular effect caused by interaction with the solar
wind and the Earth's magnetic field is The Southern Lights, or Aurora
Australis and Northern Lights, Aurora Borealis
Charged particles ejected from the Sun in solar storms strike the Earth's
atmosphere about 100 kilometres above the surface. The Earth's magnetic
field collects these particles and directs them towards the poles. These
charged particles collide with other particles in the atmosphere and
the atmosphere glows, similar to charged particles in a fluorescent
lamp. This flickering, coloured glow is seen in a roughly circular region
centred on the magnetic poles because that is where the incoming charged
particles are directed.
|