  The physics of topological insulators makes it possible to understand and
predict the existence of unidirectional waves trapped along an edge or an
interface. In this review, we describe how these ideas can be adapted to
geophysical and astrophysical waves. We deal in particular with the case of
planetary equatorial waves, which highlights the key interplay between rotation
and sphericity of the planet, to explain the emergence of waves which propagate
their energy only towards the East. These minimal ingredients are precisely
those put forward in the geometric interpretation of the Foucault pendulum. We
discuss this classic example of mechanics to introduce the concepts of holonomy
and vector bundle which we then use to calculate the topological properties of
equatorial shallow water waves.
