Lydia Baker - Spectral Lines Gizmo Digital

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Rockingham Community College *

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131

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Astronomy

Date

Apr 3, 2024

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docx

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4

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Name: Lydia Baker Date: 3-29-22 Student Exploration: Star Spectra Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: absorption spectrum, binary star, blueshift, Cepheid variable, emission spectrum, giant star, nebula, redshift, spectrum, star Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. What happens when light goes through a prism? the light reflects off of different things giving different colors This band of colors is called a spectrum . 2. A rainbow is an example of a spectrum. What is the sequence of colors in a rainbow? Red Orange Yellow Green Blue Indigo Violet Gizmo Warm-up The interior of a star produces a continuous spectrum of light, like a rainbow. Cooler gases in the outer layers of the star absorb certain wavelengths of light, causing dark lines to appear in the spectrum. The resulting absorption spectrum can tell astronomers a great deal about the star. 1. On the Star Spectra Gizmo, turn on Show labels . Select star 1 to see its absorption spectrum. How many lines do you see in the spectrum? 10 2. Drag the Hydrogen spectrum next to the Star spectrum so that the edges line up. Do some of the lines on the two spectra match up? some do, some dont 3. Drag the Helium spectrum next to the Star spectrum. Do some lines match? helium lines up with star spectrum 4. Try out the other available spectra. Do any others have lines that match? no 5. Which elements have contributed to the spectrum of star 1? Helium and Hydrogen Note: The elements in a star’s spectrum do not necessarily reflect what the star is made of. The absorption spectrum is mostly determined by the surface temperature of the star.
Activity A: Classifying stars Get the Gizmo ready : Check that Show labels is on and Neutral spectra is selected. Question: How are stars classified? Introduction: Late in the 19 th century, Harvard astronomer Edward Pickering wanted to sort and catalog the thousands of star spectra that had been collected by the Harvard Observatory. He hired several women to do the work, paying them 25 cents a day. The most prominent of these women was Annie Jump Cannon, who devised a classification system still used today. Harvard Classification Scheme Class Color Prominent spectral lines Surface Temp. (K) O Blue Ionized helium, hydrogen > 25,000 B Blue-white Neutral helium, hydrogen 11,000 – 25,000 A White Hydrogen, ionized sodium, ionized calcium 7,500 – 11,000 F White Hydrogen, ionized sodium and calcium; neutral sodium and calcium 6,000 – 7,500 G Yellow Neutral sodium and calcium, ionized calcium, ionized iron, ionized magnesium 5,000 – 6,000 K Orange Neutral calcium, neutral iron, neutral magnesium 3,500 – 5,000 M Red Neutral iron, neutral magnesium, and neutral titanium oxide (not shown) < 3,500 1. Classify : Use the Gizmo to find the elements that are present in the spectra of stars 1 through 4. Remember to check both the Neutral spectra and the Ionic spectra . Then use the table above to classify each star and describe its surface temperature. (Note: A star spectrum may not display lines of all of the elements typical of its spectral class.) Star Color Elements in spectrum Class Surface Temperature (K) 1 Blue Hydrogen and Helium O > 25,000 2 Orange Calcium, Iron and Magnesium K 3,500 - 5,000 3 Blue Hydrogen and Helium O > 25,000 4 White Hydrogen, sodium and calcium A 7,500 - 11,000
Activity B: Unusual stars Get the Gizmo ready : Select star 5 . Question: What else can we learn from stellar spectra? 1. Observe : Observe the spectra of stars 5 – 10. Identify the elements in each spectrum, and try to classify each star. If you notice unusual features in these spectra, describe them. Star Color Elements in spectrum Class Unusual features 5 Yellow None G double line like sodium, but moved 6 White Iron and Titanium M magnesium doesn't work, it has more lines than the regular magnesium 7 Blue White Helium and Hydrogen and? B Normal 8 Yellow Sodium and Calcium G light goes in and out, go up and down 9 White Hydrogen, sodium and calcium F calcium did not match, but moved occasionally 10 Yellow Sodium and Calcium G Normal Match : Write the number of the star or object that matches each description (only stars 6-10 ). Then use this information to help you identify the elements and reclassify the stars in the table above. 3 High atmospheric pressures in a star cause spectral lines to be broadened, or “smeared out.” Giant stars , which have relatively low atmospheric pressures, are characterized by many narrow spectral lines. 2 If a star is moving away from an observer, spectral lines are redshifted , or shifted toward the red end of the spectrum. An approaching star is blueshifted . 8 A star orbited by a large planet will move in a small circle. This will cause its spectrum to be slightly redshifted part of the time and blueshifted at other times. 4 Binary stars are pairs of stars that orbit one another. Their presence is indicated by two spectra that shift in opposite directions. 6 Cepheid variable stars change their brightness in a regular cycle. Gas pressure builds up, causing the stars to expand quickly. When the pressure is released, the star contracts, and the intensity of some spectral lines may decrease.
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7 A nebula is an enormous cloud of gas and dust in which stars are born. Most nebulae produce an emission spectrum , which is characterized by bright lines of color against a dark background. The bright lines in an emission spectrum correspond to the dark lines in an absorption spectrum. Assessment Questions: 1. 2. 3. 4. 5.