Every day the Earth completes a rotation around its axis. In this case there are infinitely many 24-hour periodic orbits, there are even 2 fixed points! This is a slight approximation though, as the axis of rotation is not fixed compared to the Earth’s crust, but instead wobbles with a period of roughly 8 years. Now it is no longer obvious there are some 8-year periodic orbits. Hamiltonian Floer homology can be used to show there are at least 2. In this talk I will give a brief introduction to Hamiltonian Floer homology, showing that it is basically Morse homology in disguise.