  Second part of a didactic sequence of activities on some topics of Astronomy,
related mainly with the real shape of the Earth, the gravitational interactions
between our planet and other celestial bodies, and the resulting movement of
the rotational axis of the Earth, leading to the precession of the equinoctial
points. All elements are given for the construction of a simplified Sun-Earth
system model, with a zodiacal band surrounding it, in order to show in a
pedagogical manner how precession involves a shift of the zodiacal
constellations in time.
