astronomy labs

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SPECTRA LAB Purpose: To study spectra and see how they relate stars and planets. Introduction: Spectrums are created by the emission and absorption of a photon of light by electrons surrounding the nucleus of the atom. When the photon is emitted we see separate spectra lines. When the photon is absorbed we see the continuum spectra blotted out by the black spectra lines. Each element has its own spectrum, a type of fingerprint, due to the fact each element has a differing number of electrons that can absorb or emit photons. Figure 1 shows each process.

Figure 1 A model of the Bohr atom. http://v.d.singleton.home.att.net/genchem/spectra.gif

Figure 2 Absorption and Emission Spectra of Hydrogen http://www.astronomynotes.com/light/s5.htm In astronomy we only observe objects from a distance. But in order to experience these objects we need to detect the items with our five senses; sight, smell, hear, touch, and taste. We design robotic probes and telescopes to do this, but they must be able to combine all those senses into one, sight. We do this through the science and art of spectroscopy. From one spectrum we can see, smell, touch, hear, and taste a planet or star. We start with sight. By combining the colors of a spectrum, we can see the color of the planet or star that we are observing. It is like when we combined the colors of paint when we were in art class. Second each spectrum is a fingerprint of an element and by detecting the different elements that make up

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a planet we can smell the planet. Just like we associate greens and browns with earthy smells while we feel blues are fresh and clean like the fallen snow. We can touch the planet from the intensity of the spectral lines. If they are bright or big they indicate a hot source while a smaller or dim line indicates a cooler object. The color of the source is a collaborating observation. If there are more red lines, we observe that the source is cooler. If the source is bluer, the source is hotter. Finally, if the lines waver from image to image, we see that the planet or star is undergoing change like a planet or star quake. We can tell all this from a spectrum. Below you see the electromagnetic spectrum, we see that light is much broader from what we see through our eyes. It includes the radio to the gamma-ray regions with the optical being a small part of the whole spectrum.

Figure 3 the Electromagnetic Spectrum http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec

Now we compare the visible to the solar spectrum. We notice it seems that the spectrum has lines

taken out of the continuum. That is because of amount of gas and dusts that surround the hot core of the sun absorbs the light coming from the core. Also one notices that certain wavelengths are brighter. Wien’s Law explains that the bluer the star, the hotter the star. Notice in the Sun, we see it is a middle of a road star with the brightest color being yellow. We use the spectra to determine color, temperature, and composition.

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Figure 4 the Solar Spectrum http://www.pbs.org/wgbh/nova/teachers/activities/pdf/3113_origins_01.pdf

Back in 1900’s, an astronomer called Annie Jump Cannon looked at the different spectra of stars. She categorized them by the presence of lines with in each star’s spectra. She categorized them by less lines going to more lines. The stellar types were called by O, B, A, F, G, K, M. They are shown in the Figure 6 below.

Figure 5 the Stellar Spectral types http://blueox.uoregon.edu/~courses/BrauImages/Chap17/FG17_010.jpg Finally, in the 1930’s two astronomers called Hertzsprung and Russel independently studied the temperature of stars versus the brightness of each of the stars. They came to same American Astronomical Society meeting and presented the same graph. This graph shows the life stages of the star going from proto-star, main-sequence, and red giant phase, to death as you can see in Figure 7 below.

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Figure 6 the H-R Diagram http://www.aw-bc.com/info/bennett/images/hrdiagram.jpg

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Part I: Elemental Spectra

1) After obtaining a diffraction grating from your instructor, construct the shoebox spectrometer according to the image below:

Figure 7 Shoebox Spectrometer https://www.uq.edu.au/_School_Science_Lessons/36.101.GIF

2) Open up https://www.ifa.hawaii.edu/~barnes/ASTR110L_F05/spectralab.html. Look at the spectra about mid page and enter the name, atomic number (see https://en.wikipedia.org/wiki/Periodic_table), and check mark the color of the lines present in Table 1.

3) Please take an image of one of the spectra through your box using your camera on your cellphone

of one light source around where you live (DO NOT LOOK AT THE SUN!).

Part II: Stellar Spectra 1) Open http://skyserver.sdss.org/dr16/en/proj/advanced/spectraltypes/lines.aspx. Read the page on

how we look at the stellar spectra and try to type the example stellar spectra for the correct type. Click “Next” at the bottom of the page.

2) On the next page is a list of stars with unknown spectral types. Click on the second column for each star and you will receive the following screen:

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3) Please enter the name on Table 2, note the color of the star in the image, and click on the spectra to zoom in on the spectra. Using the information from the website and Figure 6 determine the spectral type and enter this into Table 2. The dark lines in Figure 6 represent absorption lines like the one indicated above.

Part III: Hertzsprung and Russel Diagram

1) Graph the absolute magnitude (y-axis) versus the temperature (x-axis) using the data from Table 3 using Excel or similar program. Enter temperature under column A and absolute magnitude under column B. Select both and under Insert >> Chart like this:

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2) Once you insert the chart, right click on both the x-axis and y-axis and select “Format Axis” and click

on “Maximum Axis Value” and “Values in Reverse Order” like this:

3) Include this worksheet in your laboratory report.

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Data Sheet Laboratory 3 Table 1 The Spectral Colors of Particular Element Element Name

Atomic Number

Red Orange Yellow Green Blue Violet

Table 2 Stellar Spectral Types Object Name Color Spectral Type

Table 3 Stellar Temperatures for brightest stars visible from the Northern Hemisphere Common Name Temperature Absolute Magnitude

Sun 5800 4.8 Sirius 9600 1.4 Canopus 7600 -2.5 Rigil Kentaurus 5800 4.4 Arcturus 4700 0.2 Vega 9900 0.6 Capella 5700 0.4 Rigel 11,000 -8.1 Procyon 6600 2.6 Achernar 22,000 -1.3 Betelgeuse 3300 -7.2 Hadar 25,000 -4.4 Acrux 26,000 -4.6 Altair 8100 2.3 Aldebaran 4100 -0.3 Antares 3300 -5.2 Spica 2600 -3.2 Pollux 4900 0.7

http://www.astro.indiana.edu/catyp/activities/near_bright.doc

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Questions

1) Note the relationship between the number of spectral lines and atomic number. In the stellar spectra, note the number of spectral lines and temperature and the color of the star.

2) Note any patterns in the Absolute Magnitude versus Temperature plot. Compare to the Hertzsprung- Russel diagram (Figure 7 in the Introduction) from above and classify these outlier stars.