Scientific Colloquium
May 14, 2004

The Earth's magnetic field has always attracted much attention. Discovered
long ago, its dynamic were uncovered only after systematic monitoring
began in the 17th Century. The field is now precisely monitored from space
and in as many as 150 observatories worldwide. This multifaceted
phenomena, best known for orienting needles and protecting the Earth from
the solar wind, is also an invaluable source of information about our
dynamic planet. In this talk, I will introduce the various sources that
contribute to the observed magnetic field, explain how combined ground
based and satellite observations makes it possible to isolate the field of
each source and discuss some of the associated discoveries. Of particular
interest is the behavior of the main magnetic field, produced within the
Earth's liquid metallic core, and the source of most of the observed
field. The main field currently features an intensity low within the South
Atlantic. The evolution of this growing low could pose technological
challenges to the satellite developers.