1.
Orbits with same semimajor & semiminor axes, just
different couplings of spin & orbital angular momentum.
2.
No Electric Dipole transitions allowed but can have
Magnetic Dipole transitions (a factor of 137.036 slower).
3.
In neutral atoms, splitting is small & emitted photons
are
radio frequency.
4.
In highly ionized atoms, emitted photons have visible
wavelengths, & transitions are fast.