Energy in the Spectrum

We see a rather close match of the energies in the gas spectra with some of the energies of the dark lines of the star’s spectrum. These observations are a hint that the process that produced the dark lines is related to the one that produced light in gases.

A sign which photographers sometimes have on darkroom doors reads “Keep the door closed so the dark will not escape.” This joke plays on the idea that dark is the absence of light (or energy), so it cannot escape. We will use the same idea with the star’s spectrum. The dark lines are energies that are missing from its spectrum. Each of these energies has been removed while other energies are present.

To understand the processes we need to think about energy in the light. In the previous activity we saw how light is produced by energy changes in atoms. Now think about what needs to happen for one energy of light to be removed from a beam containing all energies of visible light.

Can you use the energy level diagram to describe how a photon of light can be removed from a beam of light?

A spectrum with dark lines in it is called an absorption spectrum. To help understand how absorption spectra occur we will use the Spectroscopy Lab Suite Absorption unit.