A MODEL OF THE SUN'S MAGNETIC FIELDS

CREATING A MODEL OF THE SUN'S MAGNETIC FIELDS

One of the most important skills learned by scientists is the the idea that many of the processes described and observations that have been made are difficult to visualize because of the length of time it takes for an event to occur or the dimensions of size that are involved. As a result, scientists use models to explain or predict scenarios. Models can be created that enable us to view things on a human scale that are either too small (atoms) or too large or powerful (galaxies or black holes) to view in reality. Both models of atoms and galaxies help us understand the relationship between the individual parts that may be involved and results obtained from combining the parts.

All of the following images were recorded
on the same day in 1997 using different instruments on the SOHO spacecraft.

A lesson that may be used as a warm-up to this exercise can be found here- How are Magnetic Fields Related To Sunspots?

	The image to the left is an image of the Sun from April 12, 1997 showing a view of the Sun in the extreme ultraviolet wavelengths. This image was captured by the SOHO/EIT instrument at the He II emission line at 304 Å. Notice the bright areas in the upper right quadrant and in the lower right quadrant. He II is the ionized form of helium observed when one electron has been removed from neutral helium, in this case by heat in the Sun.
	The bright areas from the EIT image above can be viewed in this image of the Sun called a magnetogram, captured by SOHO/MDI. This image indicates strength of magnetic fields. This type of image shows areas of intense magnetic activity as paired areas of dark and light. This pairing represents the poles of a magnetic field extending into the corona from below.
	This image of the Sun was taken at roughly the same time using wavelengths of light in the extreme ultraviolet using the EIT instrument on the SOHO spacecraft. Notice again, the bright areas in the upper right quadrant and in the lower right quadrant. These three images, two produced in the ultraviolet, using EIT, and one using MDI, show areas of intense activity. The image to the left has been recorded using the emission spectrum of Fe XII at 195 Å. Fe XII is the ion resulting from the removal of eleven (11) electrons from neutral iron by the heat of the Sun. As in the image viewed in He II above, the image is in false color. The actual color is beyond the range of human perception, being found outside the range of visible light in the electromagnetic spectrum.

TEACHER BACKGROUND
To solar scientists, the orientation of east and west is reversed when viewing the Sun. This result is achieved when orienting yourself by lying on the ground with your head pointing towards north.
An observation that has been made of the Sun is that sunspots are areas of intense magnetic activity. When measured by instruments such as the Michelson Doppler Imager (MDI) found on the SOHO spacecraft, these areas have been found to be composed of two parts corresponding to the poles of a magnetic field- north and south. Sunspots have been observed to have bipolar areas that appear to run along the lines of latitude of the surface. On the Sun's northern hemisphere, the paired areas have been measured to have the northern (+) magnetic pole on the western edge of the pair and the southern (-) magnetic pole on the eastern edge.	Using imagery generated from the magnetic polarity data received from SOHO/MDI instrument, it has been observed that the northern polar area (+) of a sunspot appears darker than the southern polar area. The orientation of northern and southern regions is exchanged in the Southern Hemisphere of the Sun, with the northern pole (+) on the eastern side of a sunspot and the southern pole (-) on the western end. Interestingly, the Sun's south magnetic pole is presently viewed at the norhtern geographic pole when viewed from earth, but that will change over the next solar cycle.
TRIVIA- The Earth's geographic North Pole is actually the magnetic South Pole. When using a compass, the needle end designated "N" points toward the geographic north pole, but we know that opposites attract and that the "N" directional arrow is actually pointing towards the magnetic "S" pole. (but convention prevails)

Lesson Introduction
Explain that the Sun is magnetic body and that the observed orientation of the magnetic fields appear to be along the lines of latitude. Explain also that the equator of the Sun rotates faster than the polar regions. It may be necessary to complete the lesson on differential rotation.[See Differential Rotation.]
With the students working in groups, have them spend time brainstorming a solution as to why the magnetic fields are oriented in the manner observed. Write as many solutions as are offered on the board. When the students have finished, distribute materials to each group and have them create a representation of their own model. This may take some time. It is important that the students understand that their model must describe a reversal of sunspot orientation at the equator of the Sun. It should also be understood that there may be more than one solution to the problem. After the students have built their model, they should be prepared to explain the reasoning behind it. In addition, the students could complement their model by finding collaborating observations from SOHO.

OBJECTIVE

MATERIALS for each team

3 to 4 inch styrofoam ball, pierced to fit on dowel
yarn
8-10" length of 1/4" dowel
tape or pins to fix ends of yarn onto dowel

PROCEDURE

A possible solution is provided at this site.

Connections to National Standards:

National Science Education Content Standards A, B, D, E, H:
- All students should develop abilities necessary to do scientific inquiry.
- All students should develop an understanding of structure of atoms, structure and properties of matter, motions and forces.
- All students should develop understanding of origin and evolution of the universe.
- All students should develop understanding about science and technology.
- All students should develop understanding of science as a human endeavor and historical perspectives.
Benchmarks for Science Literacy:
- Scientists assume that the universe is a vast, single system, in which the basic rules are the same everywhere. The rules may range from very simple to extremely complex, but scientists operate on the belief that the rules can be uncovered by careful, systematic study.
- No matter how well one theory fits observations, a new theory might fit them just as well or better, or might fit a wider range of observations. In science, the testing, revising,and occasional discarding of theories, new and old, never ends. This ongoing process leads to an increasingly better understanding of how things work in the world but not to absolute truth. Evidence for the value of this approach is given by the improving ability of scientists to offer reliable explanations and make accurate predictions.
- Students should know that telescopes collect information from the entire spectrum of electromagnetic waves, spaces probes send back data from the remote parts of the solar system and that increasingly sophisticated technology is used to learn about the universe.
- Magnetic forces are very closely relayed to electric forces and can be thought of as different aspects of a single electromagnetic force.
- Accelerating electric charges produce electromagnetic waves around them. A great variety of radiations are electromagnetic waves: radio waves, microwaves, radiant heat, visible light, ultraviolet radiation, x rays, and gamma rays. These wavelengths vary from radio waves, the longest, to gamma rays, the shortest. In empty space, all electromagnetic waves move at the same speed: "the speed of light."

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Author: Jerry Roth (jroth@achilles.nascom.nasa.gov)
Official NASA Contact: Dr. Art Poland(poland@pal.gsfc.nasa.gov)
NASA Home / Goddard Space Flight Center Home
Last Updated: 8/12/98