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