Table of Contents

The Solar System
Planetary Data
Terminology
Formation Theory Parameters
Magnetic Fields
Angular Momentum
Solar System Formation Questions

Intro to Astronomy
Misconceptions

Archaeoastronomy
Equitorial Coordinates
Understanding the Seasons

Telescopes  

Solar & Lunar Eclipses

The Earth

The Moon

Mecury, Venus, Mars

The Outer Planets

Solar System Debris

The Sun

Evolution of Stars

Intersteller Matter

Sky Literacy

Magnetic Fields

    The concept of a field involves a force which is created by a property or a condition of matter which goes beyond the boundaries of that material object. Gravity is a force which seems to be inherent in all material things, no matter how big or small. Although scientists have no problem quantifying the concepts of gravity, their ability to explain exactly what it is remains vague and circular in nature. The same can be said for magnetic fields which are created when electrons flow in a current or atoms are aligned so that their spin axes point in the same direction.
    All magnetic fields ultimately come from electrical charges in motion. A bar magnet has no outward sign of motion, but the circulation of electrons around iron nuclei sets up its magnetic field. One electron swirling around a nucleus generates a minuscule magnetic field. Electrons of innumerable atoms, all orbiting in the same direction, will create a magnetic field detectable at a distance away from the matter.
    You have probably seen an electromagnet in operation. Here an electric current, a flow of charged particles passing through a loop of wire, creates a magnetic field. The earth's magnetic field is probably generated by the internal circulation of electrons which are made to move in a series of loops by the fairly rapid rotation of the planet. The magnetic fields around the earth and the sun have two poles; this dipolar characteristic allows us to think of these fields as arising from giant bar magnets buried in the earth and sun.
    A magnetic field line (flux line), is a region where the magnetic field is more intense. As a concrete analogy, imagine the magnetic field lines consisting of numerous elastic bands stretched before you. Charged particles and magnetic fields interact in such a way that the particles find it difficult to cross the field lines. Instead the charged particles tend to spiral along the field lines and travel where ever the flux lines go. The direction of the spiraling plasma depends upon whether the particle is positively or negatively charged. Continuing with the rubber band analogy, if a charged particle attempts to plow across the band, it encounters resistance which stretches the field lines. The particle, instead of breaking through the band, takes the path of least resistance and spirals along the band. So charged particles and magnetic fields are linked together by their interactions.
    This linking is important for understanding what happens to a magnetic field that is immersed in an ionized gas (plasma) like the sun. If the ionized gas moves, it carries the magnetic field lines with it. For example, if the gas is moving turbulently, it tangles and jumbles up the direction of the magnetic field lines.
    Moving charged particles produce magnetic fields. In turn, magnetic fields affect the motions of charged particles. This linking of magnetic fields and charged particles has important astrophysical consequences.

Adapted from Michael Zeilik, Astronomy: The Evolving Universe (New York, 1963), 147-148.