Spectroscopic Inquiry from UC Santa Cruz


Experiments: Introduction to Spectroscpy
This 'laboratory experiment' is designed for secondary students, most likely physics/chemistry students at the Junior or Senior level although it might fit within an advanced 9th grade physical science class. The students are guided through a series of smaller experiments where they explore one or two concepts of spectroscopy. Toward the end of the lab, the students will have the choice to investigate temperature and the nature of spectral lines. Below, we detail the primary content of the lab, give an outline, and then describe the content and structure of each sub-experiment.
	Primary Content	A. Introduce the concepts of spectroscopy -- experimental design, wavelength, color, brightness B. Explore the relation between temperature, wavelength, and color C. Introduce the concepts of spectral lines

	Lesson Plan	I. Introduction (5min) Establish goals for the laboratory, split into teams of 2-3 persons II. Solar spectrum (15min) Explore the solar spectrum III. Wavelength (10min) Build an understanding wavelength IV. Directed investigation (15min) Explore the spectrum of a chosen astronomical object V. Student-led investigation (20min) Explore temperature and/or spectral lines

I. Introduction to a Spectrum
	Overview	In this portion of the lab, the students get their first experience with the software tools. In addition to this, the students are introduced to the experimental design of producing a spectrum and then the basics of a spectrum.
	Primary Content	A. Demonstrate the means of producing a spectrum B. Build the relationship between color and wavelength C. Introduce the concept of a spectrum
	Secondary Content	a. Introduce the Inquiry Tools (i.e. familiarity with the software) b. Continuous spectrum vs. spectral lines c. Explore the Sun's light
	Experimental Design	This experiment has two parts. In the first stage, the students are challenged to produce a spectrum. The initial setup is the Sun and an empty position where one aims to produce a spectrum. The student controls the placement of two optical elements: (1) a mirror which they can tilt; and (2) a prism. Once they have properly configured the experiment, a 2D spectrum (color) will appear (see screen shot above, left), and they will able to enter the spectroscopic mode of the tool. In this second stage, the students view a spectrum of the Sun and several other objects of their choosing. The spectrum is first displayed as a set of color histograms (see screen shot above, right) where the height of the bar indicates the relative amount of light emitted at that color. The student can also view the 'exact' spectrum as a solid, gray curve. The wavelengths of the light are also indicated which draws the connection between color and wavelength.
	Exercises	1. Produce a spectrum by placing a mirror and prism in their proper positions to direct light from the Sun to the 'screen' where a spectrum will appear. Sketch the correct configuration in your labbook. 2. Examine the spectrum of the Sun. Sketch the colored historgram into your labbook. At what color does the Sun emit the most light? Produce a table that orders that gives the relative height of each color, in descending order. 3. What is the wavelength of the peak in the spectrum of the Sun? 4. Turn off the histogram mode and choose another source (e.g. the Sodium lamp). What color do you predict this object is emitting at? Try another source. 5. Choose the Spiral Galaxy as the source and enable the "Exact Spectrum". Estimate the wavlength of the bright, red lines. What do you think may be causing these?

II. Wavelength
	Overview	The students utilize the Wavelength Inquiry tool to construct various types of light with differing wavelength. In particular they can stretch and compress the wavelength of the light and explore the results.
	Primary Content	A. Understand the concept of wavelength B. Understand that the various types of light are a contiuous spectrum
	Secondary Content	a. Introduce the various telescopes used to perform astronomy. b. Relate the wavelength (a size) to various 'real world' objects c. Photons
	Experimental Design	This experiment depicts a 'ray' of light whose wavelength can be modified in a number of ways. The student can stretch/compress the light with the mouse in the plot window or using one of the zoom buttons. They can also 'jump around' from type to type with the pull down window. As they produce light with significantly different wavelength, two displays are modified: (10 the telescope window is updated to show the modern facility that observes light with this wavelength and (2) the upper-right window shows an object whose size roughly matches the light's wavelength.
	Exercises	1. Draw a cartoon of light in your labbook. Indicate the distance that corresponds to the wavelength of your light. 2. Use the tool to produce an X-ray. How does this light differ from the light that we see with our eyes?

III. Directed Investigation
	Overview	The lab teams are directed to choose an astronomical object whose spectrum they will explore. The choices are: (i) a cool, red star; (ii) a hot, blue star, (iii) a blue, spiral galaxy, and (iv) a red, elliptical galaxy. They will explore the spectrum in tandem with a true spectrum of the Sun (one that includes absorption line features) using the an Spectrometer Inquiry Tool. The students are also directed to use the Spectral Lines Inquiry Tool to explore the physical origin of spectral lines.
	Primary Content	A. The connection between color and wavelength B. Introduction to spectral lines B. Physical origin of spectral lines
	Secondary Content	a. Temperature b. Galaxies are made of blue/red stars c. Atomic structure
	Experimental Design	This experiment enables the students to compare/contrast the spectrum of an astronomical object against that of the Sun. The students are directed to make both qualitative and quantitative comparisons. The students are also prompted to explore several spectral lines associated with their astronomical object and contemplate the origin of these features. Finally, they explore the physical origin of spectral lines using an additional Inquiry Tool.
	Exercises	1. Compare and contrast the spectrum of your astronomical object with that of the Sun. How are the spectra different or the same? What might be the origin of the differences/similarities? 2. Note that the spectrum of your object (and the Sun) is not a simple smooth curve. While there is an overall shape to the spectrum, there are additional sharp and narrow features (termed spectral lines) in the spectrum. Zoom in on one of these features and measure its wavelength. What do you think may be causing these spectral lines? 3. Using the "Spectral Lines" pull-down, turn on the labelling for a few of the different elements. The arrows that appear indicate the wavelengths where the various elements may emit/absorb light. Record which of these spectral lines match features in your spectrum. 4. Now launch the "Spectral Lines Tool". Explore the origin of emission and absorption lines as a function of the movement of an electron in a Hydrogen atom.

IV. Further Investigation
	Overview	The lab teams now choose one of several areas for further investigation. These are: (i) the quantiative relation between temperature and wavelength; (ii) the utility of spectral lines.
	Primary Content	A. Temperature: Wien's Law B. Spectral Lines: Doppler shift
	Secondary Content	a. Color b. Atomic structure c. Photons
	Experimental Design	Path 1: Temperature -- If students select this route, they explore the quanatitive relationship between temperature and wavelength using the Wien's Law Inquiry tool. The students are directed to explore the spectra of several stars with a range of temperature, record the wavelength of the peak of each spectrum, and then infer Wien's Law. Path 2: Spectral Lines -- The students select an astronomical object and then focus on a single spectral feature, measuring its wavelength and identifying the element that produces it. The students than vary the velocity of the source and explore how the spectrum changes. Finally, they are led to derive an expression for the Doppler shift.
	Exercises	Part 1: Temperature -- a. Examine the spectrum of the Sun again. At what wavelength does the spectrum peak? Record this value and also record the 'surface' temperature of the Sun. b. Create a new star with a temperature different from the Sun. How is its spectrum different/same? Record the wavelength of the peak in its spectrum and also the temperature. Repeat this for 4 other stars with different temperatures. c. Produce a plot of tempearture vs wavelength for your stars. What is the shape of the curve that connects the points? d. Now plot the temperature (y-axis) against the inverse of the wavelength (1 / wavelength). What is the shape of this curve? Can you intuit an equation that relates temperature and wavelength? e. Wien's Law f. Why do you think temperature and wavelength are physically related? Part 2: Spectral lines -- a. Choose an astronomical source for analysis. b. Choose a spectral line to analyze. What is its wavelength? What is the element that produces it? c. Modify the velocity of your source. What happens to the spectrum? Measure the new wavelength of the spectral line you chose. d. Now choose the same speed but in the opposite direction (negative is toward you and positive is away from you). What happened to the spectrum now? e. Repeat for a range of velocities. Plot the observed wavelength against the velocity. How would you describe the shape of this curve? f. Doppler shift