Star Spectra Gizmo Answer Key

Name: Heather Lucero Date: 04-03-2022 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? White light divides into several wavelengths and hues, including red, orange, yellow, and green. 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? The absence of light is depicted by the dark line. Red, green, yellow, orange, blue, purple, and black lines are all over the place. 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 lines 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? 3. 4. Some of them do, but not all of them. Drag the Helium spectrum next to the Star spectrum. Do some lines match? Try out the other available spectra. Do any others have lines that match? Helium does match the spectrum of stars. No, nobody else does. 5. Which elements have contributed to the spectrum of star 1? Hydrogen and Helium 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. Get the Gizmo ready: Activity A: ● Check that Show labels is on and Neutral spectra is selected. Classifying stars Question: How are stars classified? Introduction: Late in the 19th 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. Class O B Color Blue Blue-white A White F White G Yellow K Orange M Red Harvard Classification Scheme Prominent spectral lines Ionized helium, hydrogen Neutral helium, hydrogen Hydrogen, ionized sodium, ionized calcium Hydrogen, ionized sodium and calcium; neutral sodium and calcium Neutral sodium and calcium, ionized calcium, ionized iron, ionized magnesium Neutral calcium, neutral iron, neutral magnesium Neutral iron, neutral magnesium, and neutral titanium oxide (not shown) Surface Temp. (K) > 25,000 11,000 – 25,000 7,500 – 11,000 6,000 – 7,500 5,000 – 6,000 3,500 – 5,000 < 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 1 Color Blue Elements in spectrum Ionized Helium, Ionized Hydrogen Class O Surface Temperature (K) > 25,000 2 Orange Neutral Iron, Neutral Calcium, Neutral Magnesium K 3,500 - 5,000 3 Blue Ionized Hydrogen, Ionized Helium O > 25,000 4 White Hydrogen, Ionized calcium, Ionized sodium A 7,500-11,000 2. On your own: Look up Annie Jump Cannon on the Internet or in a library and read her story. Share your discoveries with your classmates and teacher. The creation of modern star classification was made possible by the cataloging work of American astronomer Annie Jump Cannon. 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 5 Yellow 6 Elements in spectrum Class None of the elements match G Red Neutral titanium oxide and neutral iron (not shown) M 7 BlueWhite Hydrogen, Neutral helium B 8 Yellow Calcium, Neutral sodium G 9 Withe Ionized calcium, Hydrogen, Neutral sodium F 10 Yellow Calcium, Neutral sodium G Unusual features Similar to sodium's double line, however they are displaced The neutral magnesium does not fit since it has some more pronounced black lines than the original magnesium. Normal The light flickers, moves up and down, and there are some unfamiliar dark lines in the neutral sodium. Calcium did not match neither ionized or neutral, besides moving sometimes Normal Match: Write the number of the star or object that matches each description. 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 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. 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.