Question

If Bohr's quantisation postulate (angular momentum ) is a basic law of
nature, it should be equally valid for the case of planetary motion also. Why then do we
never speak of quantisation of orbits of planets around the sun?

Answer 1

Explanation:

We never speak of quantization of orbits of planets around the Sun because the angular  momentum associated with planetary motion is largely relative to the value of Planck's  constant (h). The angular momentum of the Earth in its orbit is of the order of 1070h. This  leads to a very high value of quantum levels n of the order of 1070. For large values of n,  successive energies and angular momenta are relatively very small. Hence, the quantum  levels for planetary motion are considered continuous.

Answer 2

${\bf{\red{Answer:-}}}$

The angular momentum associated with planetary motion is large relative to the Planck’s constant. As the angular momentum of Earth in its orbit is of order of 1070 h which results in higher value of quantum level of order of 1070. The more is the value of n, the less will be the angular momentum and energies.

Therefore, the quantum levels of planetary motion are considered as continuous.