To understand the observational properties of cosmological models, in parti
cular, the temperature of the cosmic microwave background radiation, it is
necessary to study their null geodesics. Dynamical systems theory, in conju
nction with the orthonormal frame approach, has proved to be an invaluable
tool for analyzing spatially homogeneous cosmologies. It is thus natural to
use such techniques to study the geodesics of these models. We therefore a
ugment the Einstein field equations with the geodesic equations, all writte
n in dimensionless form, obtaining an extended system of first-order ordina
ry differential equations that simultaneously describes the evolution of th
e gravitational field and the behavior of the associated geodesics. It is s
hown that the extended system is a powerful tool for investigating the effe
ct of spacetime anisotropies on the temperature of the cosmic microwave bac
kground radiation, and that it can also be used for studying geodesic chaos
.