What are advantages and disadvantages of apparent solar time? How is the situation improved by introducing mean solar time and standard time?

Advantage:  

Apparent solar time gives the exact location of sun in the sky according to your precise location.

Disadvantage:  

As the apparent solar time changes with the change in longitude. It is very difficult to track these changes in longitude. Hence, it is almost impossible to make plan for events.

Improvement in situation:

Situation can be improved using mean solar time because due to this people living in the longitude band agree upon a standard time. In this way, it is easy to plan for events.  

absorption lines are where light has been absorbed by the atom thus you see a dip in the spectrum whereas.

emission spectra have spikes in the spectra due to atoms releasing photons at those wavelengths.

explanation: