A metal in a magnetic field has its Fermi sea sectioned into onion-like layers, shaped like cylinders. These are Landau levels, due to the harmonic oscillator motion of electrons moving in circular orbits in a magnetic field. (They're only "circular" for free electrons, and can have funny shapes for electrons in a real metal.) We show a very easy way to spot the quantum harmonic oscillator in this type of problem. The quantum nature of the harmonic oscillator leads to the quantized "Landau levels" of the electrons. Lecture Audio