Introduction to ASTRONOMY Physics 3

Nov/15/2006 Spectra Version 1 (Las Positas) Page IA- XXX

NAME______NAME______

Spectra

NAME______NAME______

Part A: Spectra (Datasheet #1 & 2)

WARNING: DANGEROUSLY HIGH VOLTAGE IS APPLIED TO THE SPECTRA TUBES (there are exposed electrical contacts that you should NEVER touch, and the tubes are also VERY HOT).

There will be a number of spectra sources set up for you to observe using a hand-held spectroscope. Half of them will be “known”, the other half “unkown” for which you will try to identify the elements from the “known” sources.

Question A-1 Known Emission Spectra (Data Sheet #1

Arc tubes will be set up (probably Hydrogen, Mercury, Neon, Sodium and Helium) displaying emission spectra. For each, sketch the spectra in the upper part of DataSheet #1, with the lines in the proper place on the scale.

(a) With the naked eye, note the color of each tube. Is this color consistent with the spectral lines seen (are there any surprises, for example appears yellow, but really it only has red and green lines)?

(b) Are all the spectra of type “emission”? Are any continuous or show absorption?

(c) Do any of the tubes have a violet line which exceeds that found in white light? Do any have a red line which exceeds than found in white light?

Question A-2 Fluorescent Light (Data Sheet #1)

As your first “unknown”, view the spectra of a Fluorescent light. Sketch its spectra structure in the lower part of DataSheet#1.

(a) What type of spectra structure does this display? (Emission, Continuous, Absorption)

(b) To the naked eye, a Fluorescent light appears “white”. Where does this come from (i.e. are there any “white” lines in the spectra)?

Question A-3 Other Unknown Spectra (Data Sheet #1)

Your lab instructor will have a number of other “unknown” sources for you to view. For each, sketch the spectra and answer the question(s) below. These sources may include (all are different)

· White Computer Screen

· Street lights (rose colored) right outside lab door

· Building Lights (white)

· Coke Machine

(a) What type of spectra structure does each display? (Emission, Continuous, Absorption)

(b) Again, consider the naked eye color, and see if you can make sense of it from the components in the spectra. Note some of these sources (n.b. the Coke Machine) may be passing through a colored glass filter (i.e. is the spectra really red, or is it white light passing through red glass)?

Part B: White Light

1. White Light Observation (full power)

· View spectra of white light under full power (120 volts)

· For each “color” determine the “center” wavelength

· Next estimate the start/end borders between the colors (e.g. the end of green should be the start of yellow)

· Calculate the for each color the: Width = End-Star

Color / Start / Center / End / Width
Violet
Blue
Green
Yellow
Orange
Red

(a) How far into the Violet (near UV) can you see before it drops off? ______nm

(b) How far into the Red (near Infrared) can you see before it drops off? ______nm

(c). Which “color” is the narrowest band? ______

(d). Which “color” is the widest band? ______

(e) Summarize: Does the white light extend as deep into the violet(red) as the most violet(red) line seen in the other spectra?

2. Change In Temperature

· Lower the Power to 50%

· Notice the change in the white light spectra.

(a) Summarize: Describe the change in the spectra (quantify any change in range, and intensities of colors, e.g. does yellow drop less than blue).

(b) Center: For full power, and 50% power, estimate the “center” wavelength of the spectra. Does this center shift at all? In what direction?

3. Filtered White Light

(a) View white light after it has passed through a colored filter. Summarize the filter’s effect (be quantitative, for example, it passes 400 nm through 500 nm and blocks the rest).

(b) If another filter is available, repeat above.

Part C: Astronomical Spectra Observations

Question C-1 Fraunhofer Lines (Data Sheet #2)

WARNING: DO NOT POINT SPECTROSCOPE DIRECTLY AT THE SUN unless its setting/rising. Instead point it at blue sky (perhaps use telescope for light amplification), the moon, or the sunlight through a tree or other obscuring device. You should be able to see many of the Fraunhofer absorption lines (the ones with Capitol letters), but not all of them (e.g. the ones with small letters).

(a) View the Spectra of the Moon or of the Sun (blue sky). Summarize which Fraunhofer lines you could see, include their wavelengths, and compare to the values listed in the table.

Question C-2 Stellar Spectra (Data Sheet #3) Design your own data sheet?

View the spectra of several stars.

Make a table of star name, and sketch any lines seen.

Lookup Spectra Class in the Starry Night Program

Summarize if the lines you see correspond to what is expected.

Reference Spectra Series

Reference Information

Stellar Spectra Data Sheet Name______

Star=______Spectral Class=______B-V=______

Part E: Laser Light

1. Prediction/hypothesis: Before doing an experiment, make a prediction!

(a) Red Filter: If you shine red laser light through a red filter what do you think will happen?

(b) Yellow Filter: How about through a Yellow Filter? Explain your reasoning!

(d) Blue Filter How about through a blue Filter? Explain your reasoning!

2. Experiment: Now actually do the experiment.

(a) Red Filter: What happened? Did it match your expectations?

(d) Blue Filter What happened? Did it match your expectations?

3. Conclusion: Summarize what is happening when you shine a red laser light through a filter.

Practical Astronomy ÓSept2006, W. Pezzaglia Fall 2006