Bohr's quantisation is proportional to h (Planck's constant). But angular momenta associated with planetary motion are of the order of $10^{70} \mathrm{~h}$. This would mean $\mathrm{n}$ $\simeq 10^{70}$. For such large values of $\mathrm{n}$, the differences in successive energies and angular momenta are so small that they are continuous and not discrete.