We provide a mathematical account of the recent letter by Tarnopolsky, Kruchkov
and Vishwanath (Phys. Rev. Lett.122:10 (2019), art. id. 106405). The new
contributions are a spectral characterization of magic angles, its accurate numerical
implementation and an exponential estimate on the squeezing of all bands as the
angle decreases. Pseudospectral phenomena due to the nonhermitian nature of
operators appearing in the model considered in the letter of Tarnopolsky et al. play a
crucial role in our analysis.