Contents
Administration
Homepage
Class Syllabus
Instructor Information
Lecture
Lecture Schedule
Class Notes
Study Guide
Lecture Links
Textbook Link
Lab
Lab Schedule
Current Events
Astronomy Questions?
Weather Information
Constellation References
Summary of Indoor Labs
Take a Solar System Tour
General
Local Astronomy Society
Physics Department
Astronomy 363
High Energy Physics
Astrophysics
Purdue University
|
Astronomy 263/264
Stars, Light and Spectra
Summary
Stars, Light and Spectra Lab demonstrates one way astronomers collect
information about the stars by analyzing stellar spectra. Nearly
everything we know about stars and the surrounding universe has been
learned by observing light -- we can't perform direct experiments on
stars because they are so far away! We can only glean information
from the light that they emit. In this lab, you will observe several
example spectra, and also identify two "mystery" elements.
Concepts
In this lab, you will be using a spectrometer
to observe spectra. A spectrometer works by spreading
light out into a rainbow, just like a prism does.
There are two types of spectra: continuous spectra and discrete
spectra. Continuous spectra look
like a continuous rainbow. Continuous spectra are given off by very
hot solids, liquids and some dense, opaque gasses.
Discrete spectra are made up of
small chunks of the continuous spectrum. Discrete spectra are given
off by excited atomic gasses. How are these different spectra produced?
Absorption spectra are the
"reverse" of the discrete spectra. By looking first at absorption, we
can understand how the discrete spectrum is formed. Normally, the
electrons that orbit the center of the atom (the nucleus) are in the
"ground state" -- the lowest energy level. An atom becomes "excited"
by absorbing light of a certain color (energy) and jumping to an orbit
further away from the nucleus. This process is called absorption.
When there are enough atoms to absorb all the light of the certain color,
we get a "gap" in the continuous spectrum, like the dark lines below:
A discrete spectrum (a.k.a. emission
spectra) is produced by the light emitted from excited atoms. Once an
atom is in an excited state, it will eventually return to the ground
state and give off light of that certain color. This is the opposite
of the absorption process.
Each type of atom has unique energy levels, and will therefore have a unique
set of colors that it will absorb or emit. By examining the spectrum of
a star, we can identify what types of atoms are in the outer atmosphere
of the star. We can also use the light emitted from nebulae to determine the
type of atoms that are in it!
Last updated on January 27, 2000.
|