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AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
THE SPECTRUM OF A STAR
Overview:Stars can be classified by using the general shape and specific lines of their spectra.
Objectives:The student will:• performasimpleanalysisofspectrallinestoclassify15spectralmodelsintofourclasses;and• comparethreeplotsofunknownstarstotheJacoby-Hunter-ChristianAtlastofindtheclosestclassification
match.
Targeted Alaska Grade Level Expectations: Science[10]SA1.1Thestudentdemonstratesandunderstandingoftheprocessesofsciencebyaskingquestions,
measuring,classifying,makinggeneralizations,analyzingdata,developingmodels,inferring,andcommunicating.
[10]SA1.2Thestudentdemonstratesandunderstandingoftheprocessesofsciencebyreviewingpertinentliterature,hypothesizing,makingqualitativeandquantitativeobservations,controllingexperimentalvariables,analyzingdatastatistically(i.e.,mean,median,mode),andusingthisinformationtodrawconclusions,compareresultstoothers,suggestfurtherexperimentation,andapplytheirconclusionstootherproblems.(L)
[10]SD4.1Thestudentdemonstratesanunderstandingofthetheoriesregardingtheoriginandevolutionoftheuniversebyrecognizingphenomenaintheuniverse(i.e.,blackholes,nebula).
Vocabulary:absorption spectrum–thepatternofdarklinesandcolorsmadewhenlightpassesthroughanabsorbing
medium,suchasagasorliquid;thedarklinesrepresentthecolorsthatareabsorbed;becauseeachtypeofatomabsorbsauniquerangeofcolors,theabsorptionspectrumcanbeusedtoidentifythecompositionofdistantsubstances,suchasthegaseousouterlayersofstars
continuum spectrum–producedbywhitelightandiscomposedofallwavelengths,orallcolors,inthevisiblespectrum
emission spectrum–theradiation,suchaslight,givenoffbyasubstancewhoseatomshavebeenexcitedbyheatorotherradiation;theatomsofdifferentelementsgiveoffradiationatspecificfrequenciesastheyreturntotheirnormalenergylevel;theradiationcanthenbepassedthroughaprism,formingapatternofcoloredbars(onebarforeachfrequency);byanalyzingthesebars,scientistscandetermineofwhatkindsofatomsthesubstanceismade
spectra(pluralofspectrum)–valuesthatvaryoveracontinuumspectrograph–aspectroscopeabletophotographorotherwiserecordspectra;theimageproducediscalleda
spectrogramspectroscope–aninstrumentdesignedtoseparatelightwavesintoaspectrum;lightentersanarrowslit,
isfocusedintoathinbeamofparallelraysbyalens,andpassesthroughaprismthatseparatesitintoaspectrum
spectrum–arangeofpossiblewavefrequencies;adistributionofthefrequenciesandintensitiesofagroupofwaves,usuallyarrangedbyfrequency
wavelength–thedistancebetweenthepeakorcrestofawaveandthenextpeakorcrest
Whole Picture:MostoftheelementswithanatomicnumbergreaterthanfouroccurnaturallyonEarth,butitistheorizedthatsomeelementswerecreatedbyprimarysynthesisduringtheearlyformationoftheuniverseandinthelater
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
THE SPECTRUM OF A STAR
formationofstars.Byexaminingstars,andthelightemitted,scientistscanusespectralanalysistodetermineelementsthatarepresentandevendeterminetheoriginsoftheuniverse.
Therearethreemaintypesofelectromagneticspectra.Acontinuumspectrumisproducedbywhitelightandiscomposedofallwavelengths,orallcolors,inthevisiblespectrum.Anemissionlinespectrumisproducedwhentheelectronsinanelementareexcitedandproducephotons.Thespecificwavelengthshowsupasacoloredlinethatactstoidentifytheelement.Anabsorptionspectrumisthepatternofdarklinesandcolorsmadewhenlightpassedthroughanabsorbingmedium,suchasthegasesintheouterlayerofstars.Thedarklinesrepresentthecolorsthatareabsorbed.Becauseeachtypeofatomabsorbsauniquerangeofcolors,theabsorptionspectrumcanbeusedtoidentifythecompositionoftheouterlayersofastar.Itcanalsobeusedtodeterminethetemperatureoftheouterlayers.
Usingaspectrograph,scientistscanliterallytakeanimageofthecompositionofastarandgeta“fingerprint”forthatparticularstar,calledaspectrum.Scientistshavecatalogeddifferentspectraandformedclassesofstars–starswithsimilarcharacteristicsandmakeup–basedonthesespectra.Thesearecalledstaratlases.Likethebarcodeactivity,theatlaseshelpscientistsstudyexistingstarsandclassifynewonesidentifiedinouterspace.
Starsareclassifiedusingletternames.Inorderfromthehottesttothecoolest,therangeisthis:O,B,A,F,G,K,M,L,toT.Thelettersareoutoforderbecauseearlyclassificationswerebasedsolelyontheappearanceofvariousabsorptionlines.Laterscientistsdiscoveredacorrelationbetweentemperatureandtheclasseswererearranged.Ifneeded,forfurtherreview,atutorialoninterpretingthespectraofstarsisat:http://spiff.rit.edu/classes/phys230/lectures/spec_interp/spec_interp.html
Materials:• STUDENTWORKSHEET:“BarCodeStellarSpectra”• VISUALAID:“ElementsintheStars”• STUDENTWORKSHEET:“IndentifyingStars”
Activity Preparation:1. Askstudentsiftheyarefamiliarwithhowbarcodesonpackagingwork.Barcodescontaininformation
basedonthelocationandwidthoftheirlines.Scientistshavelearnedtoviewstarsinasimilarmanner.Eachstarhasauniquefingerprintbasedonwhatelementsarepresent.Thisfingerprintcanbeviewedusinginstrumentationdesignedtoseparatethelightemittedfromthestarintodifferentspectrums.Thisinstrumentiscalledaspectrograph.Scientistslearnalotaboutthemake-upofstarsinthisway.
2. Usingamultimediaprojectorreviewwebsiteswiththeclassthatshowspectralanalysis.(SeeActivityPreparation)
3. HandoutSTUDENTWORKSHEET:“BarCodeStellarSpectra”andreviewthebackgroundinformation.Allowstudentstocompletetheproposedclassificationsection.
4. ShowVISUALAID:“ElementsintheStars.”Byexaminingthewavelengthsoflightemittedfromthestars,astronomerscancomparethewavelengthswiththewavelengthsofknownelementsanddeterminethemake-upofthestar.Starscomeinalldifferentsizesandcompositions.Thechartonpagetwoofthevisualaidshowsthewavelengthofelementscommonlyfoundinstars.
5. Explainmanyastronomershavecatalogeddifferentspectrabyplottingthewavelengthsandformedclassesofstars–starswithsimilarcompositionandtemperature–basedonthesespectra.Thesearecalledstaratlases.Likethebarcodeactivity,theatlaseshelpscientistsstudyexistingstarsandclassifynewonesidentifiedinouterspace.OneoftheAtlasesiscalledtheJacoby-Hunter-ChristianAtlas.Itcontainsthespectraof161starswithinacertainrange.
6. Dividestudentsintopairs.HandoutSTUDENTWORKSHEET:“IndentifyingStars.”ExplainstudentswillworktogethertodecidetheclosestmatchforunknownstarsAA,BBandCCbycomparingthemtoexamplesfromtheJacoby-Hunter-ChristianAtlas.Oncepairshavefinished,askthemtoconsultwithanotherpairtocomparefindings,thendiscussstudentreasoningbehindclassificationdecisionsasaclass.
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
THE SPECTRUM OF A STAR
Extension Ideas:1. Foramoreadvancedexercise,askstudentstovisittheUniversityofManchesterJodrellBankObservatory
site.Thissiteallowsstudentstoworkthroughdataselectiontoplotobservedspectraofstars.Visitthesiteat:http://www.jb.man.ac.uk/distance/life/sample/java/spectype/specplot.htm
2. Ifavailable,havestudentsuseGraphicAnalysissoftwaretoexaminespectrallinewavelengths.3. Askstudentstowriteamockarticleforanastronomyclubnewsletterexplaininghowtoclassifystellar
spectra using both general spectral shape and specific spectral lines.
Answers:
STUDENT WORKSHEET: “Bar Code Stellar Spectra” Proposed Classification (A, B, C or D)
Star 1
A
Star 2
B
Star 3
A
Star 4
D
Star 5
C
Star 6
B
Star 7
B
Star 8
A
Star 9
C
Star 10
D
Star 11
D
Star 12
A
Star 13
B
Star 14
C
Star 15
D
STUDENT WORKSHEET: “Identifying Stars”1. MSeries2. FSeries(mayalsoacceptAseries)3. BSeries
NAME: __________________________ BAR CODE STELLAR SPECTRA
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
Background Information:
Youareprobably familiarwiththebarcodesonsalemerchandise instores.Thecodescontainimportantinformationuniquetoeachitem.Scannersusethesecodestoquicklyidentifyandpricetheitemssoughtfor purchase.
Insomewaythesebarcodesaresimilartothespectraofstars.
Thelightemittedbystarscanbebrokenintodifferentspectra.
Astronomers use sensitive instrumentation called a spectroscope toseparatethelight.Stellarspectralooksimilartoarainbowexceptmanydarklinesalsoappear.Thosedarklinesrepresentdifferentelementsintheatmosphereofthestar.Theatomsoftheelementabsorbthelightatthatwavelengthandproduceadarkline.Eachelementhasaspecificsignature.
Allstarsofagivenspectralclasshavesimilarspectralshapesandlines.Therearesomespectrathathavenotyetbeenidentified.
Directions:
UsetheKey:BarcodestellarclassesA-Dtoclassifythe“barcode”spectraofstars1-15.Acorrectclassificationwillhaveallthekeylinesandthicknesses.Theremayalsobeotherlinespresentthatcannotbe identified.Similarly, in realstellarspectrasome linescannotyetbeidentified.Recordyourproposedclassification(A,B,CorD)inthetable.
Hint: Cut out the key for easier comparison of the codes.
Unknown star spectra bar codes 1 – 15
!
Proposed Classification (A, B, C or D)
Star 1 Star 2 Star 3
Star 4 Star 5 Star 6
Star 7 Star 8 Star 9
Star 10 Star 11 Star 12
Star 13 Star 14 Star 15
Key:
Bar code stellar classes A-D:
!
Vocabulary spectra (plural of spectrum) – values that vary over a continuum spectrum – a set of values within a continuum spectroscope – an instrument designed to separate light waves into a spectrum The visible light spectrum can be seen when light is separated using a prism. A rainbow is formed when light passes through water droplets in the atmosphere.
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
ELEMENTS IN THE STARS
Astronomersplacestarsintospectralclassesbasedonthelightemitted.Byviewingthespectra,andcorrespondingwavelengths,theelementsthatmakeupthestarcanbeidentified.Thewavelengthsofallknownelementshavebeencataloged.UnknownStarsAAandBBshowthepresenceofdifferentelements.
Unknown Star AA
Unknown Star BB
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
ELEMENTS IN THE STARS
Unknown Star CC shows yet a different set of wavelengthfingerprints.ThechartbelowliststhewavelengthofelementsintherangeshowninUnknownStarsAA,BBandCC.
Hydrogen Balmer a 6563 Metals Ca II 3933 b 4861 Metals Ca II 3968 c 4340 Hydrogen Balmer e 3970 d 4101 Helium He 1 4026 e 3970 Metals Mn I 4032 Metals Fe I 4045 Helium He 1 4026 Metals N IV 4058 Helium He 1 4388 Metals Sr II 4077 Helium He 1 4471 Metals Si IV 4089 Helium He 1 7065 Metals N III 4097 Helium He 2 4339 Hydrogen Balmer d 4101 Helium He 2 4542 Metals Fe II 4175 Helium He 2 4686 Molecular Bands CN 4215 Metals Sr II 4215 Metals Ca I 4226 Molecular Bands CH "G band" 4300 Metals Fe II 4233 Molecular Bands CN 4215 Metals Sc II 4246 Molecular Bands C2 4697 Metals C II 4267 Molecular Bands TiO 4584 Molecular Bands CH "G band" 4300 Molecular Bands TiO 4625 Metals Ti II 4300 Molecular Bands TiO 4670 Metals Fe I 4325 Molecular Bands TiO 4760 Helium He 2 4339 Molecular Bands MgH 4780 Hydrogen Balmer c 4340 Helium He 1 4388 Metals C II 4267 Metals Ti II 4444 Metals C III 4649 Helium He 1 4471 Metals C III 5696 Metals Mg II 4481 Metals C IV 4658 Helium He 2 4542 Metals C IV 5805 Metals Si III 4552 Metals N III 4097 Molecular Bands TiO 4584 Metals N III 4634 Metals N V 4605 Metals N IV 4058 Molecular Bands TiO 4625 Metals N IV 7100 Metals N III 4634 Metals N V 4605 Metals C III 4649 Metals O V 5592 Metals C IV 4658 Metals Na I 5890 Molecular Bands TiO 4670 Metals Mg II 4481 Helium He 2 4686 Metals Si III 4552 Molecular Bands C2 4697 Metals Si IV 4089 Molecular Bands TiO 4760 Metals Ca I 4226 Molecular Bands MgH 4780 Metals Ca II 3933 Hydrogen Balmer b 4861 Metals Ca II 3968 Metals O V 5592 Metals Sc II 4246 Metals C III 5696 Metals Ti II 4300 Metals C IV 5805 Metals Ti II 4444 Metals Na I 5890 Metals Mn I 4032 Hydrogen Balmer a 6563 Metals Fe I 4045 Helium He 1 7065 Metals Fe I 4325 Metals N IV 7100 Metals Fe II 4175 Metals Fe II 4233 Metals Sr II 4077 Metals Sr II 4215 Telluric Absorption bands 5860-5990 Telluric Absorption bands 6850-7400 Telluric Absorption bands 6270-6370 Telluric Absorption bands 7570-7700
NAME: __________________________ IDENTIFYING STARS
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
Directions: CompareUnknownStarsAA,BBandCCtotheJacoby-Hunter-ChristianAtlastofindtheclosestmatch.Paycloseattentiontoscale.Recordyourfindings.
1. UnknownStarAAmostresembles_______fromtheJacoby-Hunter-ChristianAtlas:
A. OSeries
B. BSeries
C. ASeries
D. FSeries
E. MSeries
2. UnknownStarBBmostresembles________fromtheJacoby-Hunter-ChristianAtlas:
A. OSeries
B. BSeries
C. ASeries
D. FSeries
E. MSeries
3. UnknownStarCCmostresembles_________fromtheJacoby-Hunter-ChristianAtlas:
A. OSeries
B. BSeries
C. ASeries
D. FSeries
E. MSeries
Unknown Star AA
Unknown Star BB
Unknown Star CC
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
O
Ser
ies
B Se
ries
NAME: __________________________ IDENTIFYING STARS
NAME: __________________________ IDENTIFYING STARS
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
A
Ser
ies
F Se
ries
NAME: __________________________ IDENTIFYING STARS
AKSCI ©2011 Alaska Department of Education and Early Development The Spectrum of a Star
M S
erie
s