BACKGROUND FOR SORTING SPECTRA
Detailed background is at http://stars.astro.illinois.edu/sow/spectra.html
http://www.colorado.edu/physics/2000/quantumzone/
http://www.colorado.edu/physics/2000/quantumzone/fraunhofer.html
Because the efficiencies of absorption depend on temperature, so do the
appearances of the spectra of the stars. Stellar spectra were first observed in the
middle of the 19th century. As an aid to understanding, astronomers began
classifying the spectra. In 1890, E.C. Pickering and assistants Annie Jump Cannon,
Antonia Maury, and Williamina Fleming categorized the stars, lettering them
according to the strengths of their hydrogen lines. As observation improved,
astronomers dropped some letters, rearranged others according to different spectral
criteria, and added numbers. The result was the seven letter sequence OBAFGKM,
representing classes from hottest to coolest. The Sun is class G.
THE SPECTRAL SEQUENCE
Class Spectrum Color Temperature
O = ionized and neutral helium, weakened hydrogen bluish 31,500-49,000 K
B = neutral helium, stronger hydrogen blue-white 10,000-31,500 K
A = strong hydrogen, ionized metals white 7500-10,000 K
F = weaker hydrogen, ionized metals yellowish white 6000-7500 K
G = still weaker hydrogen, ionized and neutral metals yellowish 5300-6000 K
K = weak hydrogen, neutral metals orange 3800-5300 K
M = little or no hydrogen, neutral metals, molecules reddish 2100-3800 K
Sorting Spectra Timeline
1. Do Life Cycle of a Star First
2. Introduction to Waves
Transverse
Longitudinal
Have out a pendulum apparatus to illustrate wavelength, resting position,
amplitude - Demo
3. Absorption Spectra
a. Give 3 kids different colored paper. Shine a flashlight through them to
the back wall. See how much light the tables on the other side of the colored
paper can see. This models the light absorbed as it travels through a cool gas.
b. Reference how electrons jump up to higher EL when they gain a photon
of light energy. Then when they fall back to their original EL, they emit this
photon of energy as light of a certain wavelength or color.
c. Show the kids the spectra cards. Put at least 2 on the overhead and
explain what the lines mean – they represent different wavelengths of light being
absorbed. This would be the wavelengths of light found in the star. The pattern
of wavelengths will tell scientists what elements are in the star.
Each element has its own unique spectra and can be used as a reference to
determine composition of stars.
d. Show the kids how to determine which spectra represent old stars, new
stars, hot stars, cooler stars
4. HR Diagram Activity
a. Do the activity on the board with the colored circles for stars.
b. Have the kids create their own HR Diagram from that
c. Talk about the patterns on the diagram and what that means
d. Do the worksheet
5. Visible Light Activity
a. Need a reference page
a. do the Lab
6. EM Spectrum
a. Show the video with discussion
b. Have them do some worksheet
7. Light Years
a. Talk about distances in space
Light Years
Astronomical Units
b. Do example calculations
c. Do the worksheet
8. Doppler Effect
9. Steady State vs Big Bang
Video – The Universe series