COLORS OF THE SUN Spectroscopy Activity http://solar-center.stanford.edu/activities/cots.html A PowerPoint presentation to accompany the Stanford SOLAR Center Spectroscope Activity For supplemental materials and supplies see: http://solar-center.stanford.edu/activities/cots.html

What is “Spectroscopy?” Spectroscopy is the study of light by breaking it down into component colors. Scientists can learn many things about an object which gives off light through spectrocospy Hand out diffraction gratings and have students look at lights, windows, each other – what do they see? [They should see some rainbow effects] = diffraction gratings break light into different colors (see Appendix for how) Turn off all lights except for a single fluorescent lamp (or some other gas lamp tube) – students should see a line spectrum of the lamp.

Build a Spectroscope 1) The diffraction grating allows us to view the component colors of light but it is cumbersome to hold a grating up – we need to put it in a device to make it easier to use: a Spectroscope

1. Cut out pieces & fold Cut along all of the red lines to separate the pieces of the spectroscope. You should now have 8 pieces: Spectroscope body Gap Edge Spacers(2) Diffraction Grating Eyepiece Numbered Scale Scale Cover Write your name on the colored side of the spectroscope body where it say “This spectroscope belongs to:” These instructions are found on the back of the poster. Students can read the steps on the screen or on their own instruction sheet. Be sure to keep the class on the same step – if some students finish the step early have them help another student.

2. Assemble Spectroscope Body With the black side up, use a straight edge to crease the spectroscope body along each of the grey dashed lines. Then fold the spectroscope body closed (with black side in). Put flap B over flap A so they overlap and tape edge as shown

3. Form wide scale side of Spectroscope On the wide, open side there are two long flaps labeled flap C and flap D. Fold down flap D; then fold down flap C over it. Tape flap C as shown. Then fold down the small end tab and tape corners as shown.

4. Finish end of spectroscope Fold down the end tabs, then fold Flap C down over the end tabs as shown. Tape the corners of the end as shown.

5. Make entrance slit Light must enter the spectroscope through a gap formed between flap C and the gap edge. The gap is called the entrance slit. READ CAREFULLY: it is important for the gap to be straight and narrow, so you will need to use the spacers. Stack both spacers and sandwich them between flap C and the gap edge as shown. Hold the gap edge tight against the spacers and tape on the spectroscope. Then remove the spacers from the gap. You should be able to see through the slit and it should be two thicknesses of the poster paper. Note: the slit will be a little off-center but this is O.K.

6. Align & attach grating and eyepiece At the narrow end of the spectroscope, fold the end tabs to form a square opening and tape as shown. Next, cover the square opening with the diffraction grating. Before taping, make sure your diffraction grating is aligned so that the word “Warning” is facing out and cover the “Warning” on the bottom end tab. Tape the correctly aligned grating securely in place. Tape the eyepiece over the grating with the “Warning” aligned.

7. Position scale Place the numbered scale so it covers the open side of the spectroscope. When viewed through the eyepiece, the 3000 end should be closest to the slit. DO NOT TAPE UNTIL STEP 8. Holding the scale in place while looking through the eyepiece, aim the spectroscope so you can see a fluorescent light through the slit. (It must be a fluorescent light, an incandescent light bulb will not work) You will se colored lines on the scale – these are spectral lines. If the spectral lines appear above the slit instead of over the scale, rotate the diffraction grating ¼ turn.

8. Calibrate spectroscope Slide scale back and forth until dashed line at 5450Å is aligned with green spectral line from fluorescent lamp. The tape scale in place. Finally place scale cover over the scale and tape it only along the top edge. That way you can lift the scale cover if it is too dark to read the scale.

Congratulations! Your spectroscope is fully operational. Look at various sources of light with your spectroscope. NEVER LOOK DIRECTLY AT THE SUN. (and if you do, don’t do it with your remaining eye) The spectroscope is ready to use. Let students examine the spectra of various sources of light (e.g.. Fluorescent lamps, incandescent lamps, sunlight, and if you have one handy – a Neon sign) Warn the students that the diffraction grating is not a filter and will not protect their eyes from intense light sources like the Sun or a Laser – if you want to view the spectrum of sunlight or laser light look at an object which is illuminated by that light.

Activities Look at various sources of light and draw the spectrum that you see on the provided worksheet. Some suggestions are: Fluorescent lamps Light bulbs TV’s or computers A white object in sunlight A colored object in sunlight The Moon 1) After having the students examine some light sources in the classroom, have them color in the spectroscopy worksheet to indicate what they see. NOTE: if they use colored pencils it makes a more attractive spectrum worksheet. 2) Send them out to look at sources of light around them. Remind them to be careful – the spectroscope does not protect your eyes form intense light sources such as sunlight or laser light. If you wish to view the spectrum of the Sun, look at a white object (such as pavement, walls, or clouds) illuminated by the Sun. As an interesting test, look at colored objects illuminated by sunlight – do you see a difference? Why or why not? 3) Give the students a blank worksheet and pick six light sources of their own to view and draw. Encourage them to be creative and safe. The next class meeting the students can bring back their worksheets and describe the object they looked at and show the spectrum.

Appendix A: Sample Spectra Solar Hydrogen Helium Sodium Calcium Mercury Neon Argon Water These spectra are found on the spectroscope body - they illustrate what you expect to see if you look at the spectrum of various gases or the Sun. However, with these SOLAR Center spectroscopes it is very difficult to see the dark lines on the Solar spectrum. These lines are visible with higher precision spectroscopes. Students should try to identify the type of gas which produces the spectrum that they see.

Appendix B: How does it work? Light enters the slit (white line) and as it passes through the diffraction grating it is split into component colors: each color goes in a slightly different direction (solid Blue, Green and Red lines) When you look through the grating it appears that the various colors of light are coming from different locations on the scale (as indicated by dashed blue, green and red lines). Note: the light is not coming from the scale direction, it only appears to be coming from that direction because it bends as it passes through the diffraction grating. WARNING: since the light is bent but not filtered as it passes through the grating, this does not protect your eye. Never look at anything with the spectroscope that you wouldn’t (or shouldn’t) look at with your naked eye!

Appendix C: What is diffraction? Diffraction separates light into colors by bending the light so each color of light goes in a slightly different direction The angle light bends depends on the wavelength and the distance between the slits. Since each color of light has a different wavelength, each color goes in a different direction. Red having the longest wavelength is bent the most.