When
astronomers take spectra from an astronomical object, they can see either an
emission or an absorption spectrum. By identifying the lines they see in their
spectra with catalogues of lines known to be emitted by different elements,
they can "fingerprint" the elements. In this way they can understand
what elements make up a star or a gas cloud. This is a pretty remarkable
achievement considering the zillions of miles between us and the stuff in
distant reaches of space. It is like having a doctor look at the clothes you
are wearing from 2 miles away and then telling you what you ate for lunch. This
applet lets you play around with the basic ideas behind emission and absorption
spectra as well as the Bohr model of the atom. The applet lets you build your
own orbits around an atom and then examine its spectra. The steps to follow
could go something like this.
1. You have four orbits
to play with. Choose an orbit by clicking on the buttons labeled 1 through 4
below the atom. Now change the size of that orbit by moving the slider bar.
Notice that orbit 1 always has to be smaller than orbit 2 and so on. By
sequentially playing with the four orbits, you can make any set of orbit sizes
you want.
2. The electron always
starts in the lowest orbit. Below the spectra on the right, choose the
"destination" orbit to which you want to jump.
3. Click
"jump" and watch what happens. How does the orbit change? How does
the spectrum change?
4. Repeat as often as
you want, making jumps up and down between orbits. It's better to create your
orbits first and then explore all the spectral lines associated with them, but
you can change an orbit's size anytime you want. Notice also that some jumps
will produce spectral lines so far in the infra-red (such long wavelengths)
that they fall off the spectral range represented on the applet.
5. Clear the spectra by
hitting the reset button.