GEG 1220 Compass Navigation and Magnetic Declination

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GEG 1220Compass Navigation and Magnetic
Declination

• Dr. Walter Goedecke
• Fall 2007

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Compass NavigationTopics

• Basic Compass
• Geomagnetism and the Earths Dynamo
• Earth-Sun Interactions
• Aurora
• Magnetic Declination True vs. Magnetic North

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Compass NavigationBasic Compass

• A compass, when level, has a floating, balanced
  magnetic needle that pivots in the Earths
  magnetic field.
• This is also referred to as the geomagnetic
  field.
• Source The Mountaineers Online

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Compass Navigation Terrestrial Geomagnetism

• The geomagnetic field can be approximated by a
  simple dipole magnet in the middle of the Earth
• The magnets south end actually points to the
  North Pole, and the north end points to the South
  Pole.

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Compass Navigation The Earths Dynamo
CIRES
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Compass Navigation Magnetic Multipole Moments

• The Earth actually has additional magnetic
  moments beyond a simple dipole - these are
• Quadrapole moment
• Octapole moment
• 16-uple moment
• Etc.

• Although each successive moment is more complex,
  it is weaker than the previous one

CIRES
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Compass Navigation The Source the Earths
Dynamo

• The source of the geomagnetic field is a poorly
  understood self-sustaining dynamo, probably due
  to currents within the liquid core
• All the other terrestrial planets within this
  solar system do not have a planetary magnetic
  field, although some may have in the distant past
• Most of the gas giant planets have a powerful
  magnetic field surrounding them, as does the Sun

The Earths Structure http//www.lhs.sad49.k12.me.
us/ljhs/Website20Resources/earth's_structure.htm
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Compass Navigation Sun - Earth Interaction

• The geomagnetic field is pushed by the solar wind
  and interplanetary magnetic field, so solar
  storms can affect magnetic readings.

• Solar-terrestrial diagram, showing Earths bow
  shock IMF, and magnetosphere. Source Space
  Environment Center, NOAA, http//www.sec.noaa.gov/
  info/SolarEffects.html

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OVERVIEW OF SPACE ENVIRONMENT - Aurora

• Aurora is due to the bombardment of solar wind
  charged particles along magnetic field lines into
  the polar geomagnetic footprint.
• These particles then can interact with the upper
  atmosphere where the magnetic field enters the
  Earth, in the polar regions.
• These charged particles strike the molecules and
  atoms of the thin, high atmosphere, causing
  energized atomic states.
• When the atoms then relax to its lower ground
  state, energy is released as a photon, or light.

Source Exploratorium, San Francisco, CA,
http//www.exploratorium.edu/learning_studio/auror
as/difcolors.html
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OVERVIEW OF SPACE ENVIRONMENTAurora
Aurora highlights conjunction planets from photo
by Keith Cooley in Athens Alabama on April 6,
2000, at 830 p.m. CDT. Source Space Science
News, NASA, http//www.spacescience.com/headlines/
y2000/ast25apr_1m.htm
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OVERVIEW OF SPACE ENVIRONMENTCoronal Mass
Ejection Effect - Aurora
Juergen Rendtel snapped this photo from Marquardt
(near Potsdam), Germany, from April CME
event. Source Space Science News, NASA,
http//www.spacescience.com/headlines/y2000/ast25a
pr_1m.htm
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• Five magnetometer stations in the Western US

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Magnetic Declination

• Since the magnetic poles are not coincident with
  the true poles, compass readings need correction.
• This correction is the magnetic declination.
• The magnetic north appears east of true north in
  the western US, and west of true north in the
  eastern US.
• The dividing line is approximately the
  Mississippi River.

• The magnetic poles also drift with respect to
  time.
• The north magnetic pole is drifting
  north-northwest.

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Compass NavigationReferences

• The Mountaineers Onling, http//www.mountaineers.o
  rg/navigation/
• National Geophysics Data Center, NOAA,
  http//www.ngdc.noaa.gov/seg/geomag/icons/us_d_con
  tour.jpg
• Shawhan, S.D., Solar System Plasma Physics III