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 stars
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 stars 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.