Im doing this specifically in terms of the Zeeman effect, but in general I have read some stuff about osciallations and orientations that is confusing me. If we have a magnetic dipole, propagating a field in all 3 spatial directions, and then we apply an external magnetic field in one direction, the external field would apply torque to the dipoles such that they align with the field - effectively giving them energy. which means we have 3 different energies, hence 3 different angular frequencies. in terms of the zeeman effect, this corresponds to the 3 spectral lines. we can detect these energies as light. if observed perpendicular to the field, we get 3 lines, and if viewed parallel we get 2 (transverse and longitudinal zeeman effect). but why? I really dont understand this logic. and this is where my question above comes into play...i read in a few places that for the longitudinal zeeman effect, with the field and observational direction parallel, the magnetic dipole along that direction is $$\textit{oscillating}$$ but not $$\textit{radiating}$$ - hence it is not detected, and only 2 lines are observed. what is the difference between oscillation and radiation? i can intuitivey `see' how oscialltion conserves the energy, and radiation by definition radiates it out, but in this context I cannot distinguish between the 2. why does it radiate when observed perpendicular, but not radiate when observed parallel to the field?

I know this is messy, i'm quite confused. Any help is appreciated!

An oscillating electric charge emits electro-magnetic radiation. However, the spatial distribution of this radiation is not uniform, but has a strong preference angle

copied from here. Thus, the dipole does not radiate in the direction of its oscillation.

• perfect - thank you so much! this is exactly what was confusing me. everything is clear now. Jan 19, 2020 at 15:00