Origin of ferromagnetism. Positive and negative exchange. Superexchange, molecular field theory of antiferromagnetism. Analogies with dielectric properties of solids. Energy bands and carrier concentration.
Gravitational forces determine the movements of the stars within a galaxy.
Several aspects of this basic problem will be considered, such as space distribution of stars, stellar velocity distribution, high-velocity stars, rotation curve of stellar systems, integrals of motion, individual stellar orbits. The stars moving around in elliptical galaxies exhibit triaxial velocity ellipsoids, while the ordered motion in disk systems gives rise to spiral density patterns. The stellar movements indicate that large amounts of unseen mass may be associated with galaxies and with clusters of galaxies. Many details of stellar dynamics become evident in the close surroundings of our own Galaxy where a large body of observational data assists our understanding. Stellar structure and evolution are regulated by the opposing effects of gravity and radiation pressure.