This activity was developed by NOVA as a Student Activity to accompany the NOVA movie Magnetic Storm. Understand that the Earth’s magnetic field not only changes magnitude, but also direction over time.
During this activity, students will use a hand-made magnetometer to identify and describe positions of strong magnetic field on models of the Sun. The TXESS Revolution is funded by the NSF Opportunities for Enhancing Diversity in the Geosciences program under NSF Grant 0703687, the Shell Oil Company through a grant to the Texas Regional Collaboratives for Excellence in Science and Mathematics Education, and the Jackson School of Geosciences at UT Austin. The red (North) tips of the compass needles are therefore attracted to the blue (south) pole of the Earth. Earth magnetic field lines (magnetic meridians) or lines of force are vectors with direction and intensity.
Due to its irregularity and ever-changing nature, the earth's magnetic field needs to be constantly measured (by sattelite and worldwide observatories) in order to get an accurate picture of its distribution and changes over time. The Canadian Geomagnetic Reference Field (CGRF) is a regional model specific to the magnetic field over Canada and its surroundings.
Using the dipole analogy, the magnetic poles are defined as areas where dip or inclination (I) is vertical and horizontal intensity (H) is zero. Magnetic poles experience long-term movement or secular variation, diurnal movement, as well as more rapid shift and variations due to magnetic activities originating from the sun such as magnetic storms.
As mentioned above, the dipole analogy is a simplified description of the earth's magnetic field which is a good approximation for up to 90% of the real field. The images below show the compass needles overlayed on magnetic field lines (horizontal component) in Google Earth for years 1900, 1990 and 2010.

The compass needle does not point toward geographic north pole nor does it point directly toward magnetic north pole. The angle between true north (the line towards geographical north pole) and the direction towards which the compass needle points is called magnetic declination. Again it is evident how the compass needle direction and consequently magnetic declination changes with location and time. We will use the procedure described in the National Center for Atmospheric Research Climate Discovery Teacher’s Guide on Magnetic Sun. Any opinions, findings, and conclusions or recommendations expressed on this Web site or found in the materials provided are those of the TXESS Revolution investigators and do not necessarily reflect the views of our sponsors, including the National Science Foundation. This magnetic field is similar to a dipole field generated by a bar magnet with a north and a south pole. The field is not completely dipolar and it changes (its rate of change changes as well) with both location and time. In this video, Lisa Tauxe from the Scripps Institution of Oceanography discusses the nature and origin of the earth's magnetic field, measuring and mapping its strength, and tracking its variations. The magnetic field vector at each location is described by seven components: total intensity (F), vertical intensity (Z), horizontal intensity (H) with its north (X) and east (Y) components, inclination (I), and declination (D). Based on such observations, magnetic field reference models are developed to describe the magnetic field and its changes in the future. A magnetic field calculator based on a specific model can be used to calculate different elements of the magnetic field for a desired location and time.
Magnetic meridians enter the earth vertically at the magnetic north pole and leave the earth vertically at the magnetic south pole.

The real magnetic field however is different than the dipole field and this difference is particlulary pronounced near the magnetic poles.
The field lines converge (point vertically downward) at the north magnetic pole and emanate (point vertically upward) from the south magnetic pole.
Therefore the magnetic poles are not located in the same place as the north and south geographic poles of the earth. Two main worldwide models are the International Geomagnetic Reference Field (IGRF) and The World Magnetic Model (WMM). Examples include a calculator based on IGRF model, a calculator based on CGRF and IGRF models and a calculator based on the WMM model. Check Geological Survey of Canada Geomagnetism tutorial for an explanation of this difference. The imaginary bar magnet has an axis with a tilt of about 11 degrees compared to earth's axis of rotation and is offset from Earth's centre by about 550 kilometers. The generation of such a magnetic field is explained by a dynamo process due to the movement of the fluid (molten iron) outer core of the earth. As an introduction to exploring Earth’s magnetic field, we will do a short activity on Visualizing Magnetic Fields using the NOVA worksheets.

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Rubric: Electromagnetic Pulse Shield


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