Assignment B2 Instructions & Worksheet (1)

Assignment 2: Spectroscopic Observations and Spectroscopic Data Analysis Read the Openstax Astronomy chapter titled “RADIATION AND SPECTRA” (Chapter 5). The spectrum of an object reveals a lot of information about the object emitting the light. As examples, one can deduce the temperature, pressure, composition, density, and possibly the magnetism from the light from a hot gas (like the Sun). To illustrate this, you will use a simple diffraction grating slide to make some spectroscopic observations. In Part I of this assignment you will explore the continuous blackbody spectra. Stellar spectra a based on blackbody spectra with emission and absorption features overlayed on the blackbody spectrum. For this Assignment you have two options for Part II. Option 1 uses a diffraction grating that cost a few dollars and you look at different light sources you find around the house and around town. Option 2 is analyzing stellar spectra but you will not see the colors of the spectra. Advantages Disadvantages Option 1 You can take photos to supplement the descriptions. Depending on the types of light around your house you can complete it more quickly. You need to get a diffraction grating. You need to describe what you see in detail. Make the reader see what you see. Option 2 Everything you need is in this file. You will need to figure things out based on the descriptions of the types of spectra. Part I Blackbody spectrum (mandatory) You will need to use the Blackbody Spectrum PhET Interactive Simulation from the University of Colorado Boulder. This simulation will run in your web browser. The shape and peak wavelength of a blackbody spectrum are determined by the temperature of the object emitting the blackbody spectrum. In the simulation you will notice that as the temperature of the object changes so does the color of the object. The simulation uses micrometers (μm) to show wavelength. The prefix micro (represented by a lowercase mu, μ) represents 10 -6 or 0.000001. This means 1 μm = 1000 nm or 1 μm = 0.001 mm. In photography and video production you may encounter the term color temperature. Many household lights also list a color temperature on their packaging. The color temperature tells you the lighting conditions in the visible part of the spectrum are the same as the as if the light was coming from a blackbody with that temperature.

Table 1: Unit Prefixes Prefix name Prefix symbol Factor Factor tera- T 1000000000000 10 12 giga- G 1000000000 10 9 mega- M 1000000 10 6 kilo- k 1000 10 3 Base unit None 1 10 0 mili- m 0.001 10 -3 micro- μ 0.000001 10 -6 nano- n 0.000000001 10 -9 pico- p 0.000000000001 10 -12 hecto- h 100 10 2 Use of prefix discouraged. centi- c 0.01 10 -2 Use of prefix discouraged. Part IIa Spectral Observations (option 1) You will need a linear diffraction grating with either 1000 lines/mm or 500 lines/mm. If you did not get one via the book store they are available online for a few dollars. Do not get a double axis diffraction grating. See figure 2 for the Your diffraction grating will only show the spectra of bright objects ( but again you are cautioned not to look at the Sun ). You will be able to see the spectrum of the sun during the Figure 1: The Blackbody Spectrum PhET Simulation.

The spectrum you see from an incandescent bulb is a continuous spectrum . That is, all of the visible light colors are present. However, although it is difficult to see, not all the colors are equally bright. Careful measurements show that the brightest part of the spectrum depends on the temperature of the bulb filament. A fainter low-wattage bulb will have a more yellow- orange color and a brighter, higher wattage (hotter filament) one will be bright white. subpart 1 - Diffraction Grating Experiment 1 Continuous Spectra Use the diffraction grating to look at the spectra of a traditional incandescent high wattage (60 w or more) bulb and a low output one. Can you see any color difference in the light when just using your eyes or a spectral difference when you use the diffraction grating?  Record your observations in the appropriate section of the Observing Record Form for Assignment 2 - Unit B. There is the same color effect for stars: stars with cooler surface temperatures are reddish in color, somewhat hotter ones are orange or yellow, and the hottest ones are bright blue-white. Were you able to see any colors in your observations of stars with your telescope in the previous activity or in the observations you did in Unit A? subpart 2 - Diffraction Grating Experiment 2 Emission Spectra Figure 3: The spectrum on the left of the object. It is a mirror image of the spectrum on the right of the object.. Figure 4: The spectrum on the right of the object. It is a mirror image of the spectrum on the left of the object.. Figure 5: The spectrum on the right of the object. It is a mirror image of the spectrum on the left of the object..

Next, use your grating to look at both a fluorescent bulb and a bright mercury or sodium vapor street light. You should observe streetlights from at least 30 feet away. You will notice the spectrum of this light source has only some colors, or has bright spots in the spectrum. The visible colors are somewhat separated. This is an example of an emission spectrum . You can see two spectra in the picture above from the two light sources on the far right of the image. The colors present and their pattern are characteristic of the chemical element (such as mercury or sodium) in the lamp. Look at http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/atspect.html for examples of other emission spectra.  Describe the emission spectrum you observed in the appropriate section of the Observing Record Form for Activity 2 - Unit B. In astronomy, the spectra of stars and other objects is used to determine their chemical compositions. Most stars, however, do not have an emission spectrum but rather an absorption spectrum . The light emitted from the star’s surface has all colors (a continuous spectrum) but the star’s atmosphere removes the characteristic pattern colors of the chemical elements present. This produces a spectrum with some “missing” colors, and the pattern of missing lines reveals the chemical composition of the star’s atmosphere. subpart 3 - Diffraction Grating Experiment 3 Other spectral observations Look with your eyes and through the diffraction grating at various bright light sources: different light bulbs, street lights, fluorescent lamps, LED lights, the moon, planets and stars. You will probably find that you are not able to see the spectra of astronomical objects, other than the moon, because the light is too weak. Astronomers usually obtain spectra using a large telescope, which gathers lots of light. Nevertheless, with your naked eye or using your grating you should be able to distinguish different colors for some of the brighter stars. You can try holding the diffraction grating over the eyepiece end of the telescope when you look through it at the stars to see if that helps to see their spectra. Definitely look at the moon using the diffraction grating. What you are seeing is reflected sunlight, so you can infer the sun’s spectrum from light reflected from the moon. Note: Star light is relatively dim. Looking at stars with the naked eye or a low power telescope Figure 6: Two emission spectra from the two light sources on the right.

Vega Nova Oph 2015 Menkalinan Figure 8: A spectrum of Vega. Figure 9: A spectrum of object Nova Oph 2015.

Bet LYR Regulus Mirach Figure 10: A spectrum of Menkalinan. Figure 11: A spectrum of bet LYR. Figure 12: A spectrum of Regulus Figure 12: A spectrum of Regulus

Observation Record Form for Activity 2 – Unit B Part I Blackbody lab (Mandatory) Directions : Go to the University of Colorado Boulder PhET interactive simulations website at https://phet.colorado.edu/en/simulations/browse . Open the Blackbody Spectrum simulation. Make sure to check the “Graph Values” and “Labels” check boxes. See Figure 1. Set the simulation to a temperature of 4500 K. 1. What is the most intense wavelength at 4500 K (in units of μm)? Answer: μm 2. What is the Spectral Power Density at the most intense wavelength at 4500 K (in units of MW/m 2 /μm)? Answer: MW/m 2 /μm Now move the white dot to 0.777 μm but keep the temperature at 4500 K. 3. At 4500 K what is the Spectral Power Density at 0.777 μm Answer: MW/m 2 /μm Set the simulation to a temperature of 6500 K. 4. What is the most intense wavelength at 6500 K (in units of μm)? Answer: μm 5. What is the Spectral Power Density at the most intense wavelength at 6500 K (in units of MW/m 2 /μm)? Answer: MW/m 2 /μm Now move the white dot to 0.777 μm but keep the temperature at 6500 K. 6. At 6500 K what is the Spectral Power Density at 0.777 μm Answer: MW/m 2 /μm 7. At what temperature is the peak intensity at 0.580 μm? Answer: K Part IIa Spectroscopic Observations (Option 1) You only need to do Part IIa or Part IIb. Directions : Save this form to your computer and then fill in your data and observations in the appropriate places. For each observation, be sure to give the date, approximate time, the item observed, and a detailed description. Make sure the description paints a picture in the readers mind. A photo will go a long way with your description. Observe:  a total of seven spectral observations  at least two different continuous spectra  at least two different emission spectra  at least one celestial source

 at least two other light sources that you have not observed above these may be emission, absorption, or continuous spectra. Date(s) spectroscopic observations carried out: Approximate time of the tests: Spectrum Light sources observed Description of what was seen Continuous spectrum observations Emission spectrum observations Other spectrum observations Notes and comments (if any) If you can, take a photo of an incandescent bulb through the diffraction grating and include it here. Part IIb Spectroscopic Data Analysis (Option 2) If you choose to do Part Iib instead of Part Iia answer the the following 10 questions.

Table 2: CompleteUnit Prefixes Prefix name Prefix symbol Factor Factor quetta- Q 1000000000000000000 000000000000 10 30 Added in 2022 ronna- R 1000000000000000000 000000000 10 27 Added in 2022 yotta- Y 1000000000000000000 000000 10 24 zetta- Z 1000000000000000000 000 10 21 exa- E 1000000000000000000 10 18 peta- P 1000000000000000 10 15 tera- T 1000000000000 10 12 giga- G 1000000000 10 9 mega- M 1000000 10 6 kilo- k 1000 10 3 Base unit None 1 10 0 mili- m 0.001 10 -3 micro- μ 0.000001 10 -6 nano- n 0.000000001 10 -9 pico- p 0.000000000001 10 -12 femto- f 0.000000000000001 10 -15 atto- a 0.000000000000000001 10 -18 zepto- z 0000000000000000000 01 10 -21 yocto- y 0.000000000000000000 000001 10 -24 ronto- r 0.000000000000000000 000000001 10 -27 Added in 2022 quecto- q 0.000000000000000000 000000000001 10 -30 Added in 2022 hecto- h 100 10 2 Use of prefix discouraged. centi- c 0.01 10 -2 Use of prefix discouraged. deca- da 10 10 1 Use of prefix discouraged. deci d 0.1 10 -1 Use of prefix discouraged.