Photon Emission from Atoms:
We have now completed our preliminary investigation of stellar flux and
stellar color and how those are measured. The next available measurement
to us is spectroscopy. Spectroscopy is the term given to an instrument that is
able to disperse and objects light into its component colors (wavelengths).
A prism is a simple example of such a device that splits white light into its
component broadband colors. This is done through a process known as
diffraction and it’s exactly the same process produced by water droplets in
the atmosphere as they interact with sunlight to produce a rainbow.
However, we want to disperse the light into much higher resolution
wavelength regimes than those that define a single, broad band color.
Typically an astronomical spectrum of an object will disperse the light into
several thousand discrete wavelength regimes, so as to better define
important features that are sensitive to the physical properties of a star (in
particular, its chemical composition but also its atmospheric temperature).
In this section, we will deal specifically with the formation of spectral lines
in the atmosphere of stars. These spectral lines occur as a direct result of the
structure of atoms, which we now want to examine in more detail. Here is an
alternative overview of this subject that you can refer to in addition to the
material below.
The entire key to understanding the formation of spectral lines lies in the
early 20th century discovery that each atom has a unique set of atomic energy
levels. The basic ideas of atomic energy levels and transitions will become
clearer when you run the simulation. For now, the details are summarized in
the diagrams below. We begin with the simple concept of Energy levels in
an atom as shown below
