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THE REASON FOR THE
SEASONS
HowdoesthesuncauseEarth'sseasons?
OVERVIEW
Studentsusepolystyrenefoamballsandlightbulbstoinvestigatethesun's
intensityonthesurfaceoftheEarth.
Forthecompleteactivitywithmediaresources,visit:
http://www.nationalgeographic.org/activity/the-reason-for-the-seasons/
Program
DIRECTIO NS
1.Activatepriorknowledgeaboutseasonsandsunlight.
ExplaintostudentsthattheEarthorbitsanidealdistancefromthesun,andthis
affectstheweatherweexperiencehereonEarth.Ask:Whatarethedifferent
seasons?Writethesequenceoftheseasonsontheboardforstudents’
reference:winter,spring,summer,autumn.Ask:Whatistheweatherlikeduring
thedifferentseasons?Whatisthesameordifferentabouttheseasons?Prompt
studentstoincludesimilaritiesanddifferencesinweather,temperature,and
lengthofdaylight.Writetheirideasontheboard.Thenexplaintostudentsthat
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theanswertothatquestionisdifferentforthosewholiveinadifferent
hemisphere,orhalfoftheEarth.Ask:Whatdoyouthinkcausesthedifferencein
seasons?Whatdoyouthinkcausesthedifferenceinwhattimeitgetsdark
outside?
2.Buildbackgroundaboutwhatcausesseasons.
Useaglobeandgesturetointroducethevocabularytermstiltandaxis,the
imaginarylinebetweentheNorthandSouthPoles.Thenexplainthefollowingto
students:TheEarthrotatesonanaxisthatistilted.Inotherwords,ourplanet
neverstandsupright—itisalwaysleaningtotheside.Thedirectionofthislean
doesnotchangesignificantlyoverthecourseofayear,butitdoesshift
graduallyovermillennia.AstheEarthtravelsalongitsorbit,itsometimesleans
towardthesunandsometimesawayfromthesun.Displaythediagram
“Seasons”forstudents,andpointtothepartsofthediagramasyouexplainthe
following:IfyouliveintheNorthernHemisphere,youliveonthepartofthe
EarththatisnorthoftheEquator.WhentheNorthernHemisphereistilted
towardthesun,youexperiencesummer.WhentheNorthernHemisphereis
tiltedawayfromthesun,youexperiencewinter.Ask:Howwouldthischangeif
youlivedintheSouthernHemisphere?(Theoppositewouldhappen.Whenthe
Earth'saxisistiltedtowardthesunfortheNorthernHemisphere,thepeoplein
theNorthernHemisphereexperiencesummer,whileatthesametime,the
SouthernHemisphereistiltedawayfromthesunandthepeoplethere
experiencewinter.WhentheNorthernHemisphereexperienceswinter,the
SouthernHemisphereexperiencessummer.)
3.Introducethehands-onactivity.
Dividestudentsintosmallgroupsofthree.Provideeachgroupwithone
polystyrenefoamball,onemarker,oneflashlight,andtwopushpins.Have
groupschoosewhowillholdthefoamballthatrepresentstheEarthandwhowill
holdtheflashlightthatrepresentsthesun.AskthestudentholdingtheEarthto
drawacirclearounditsmiddletorepresenttheEquator,anddotsontheNorth
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PoleandSouthPole.Havethethirdgroupmemberplaceapushpin,
representingaperson,midwaybetweentheEquatorandtheNorthPole,and
anotherbetweentheEquatorandSouthPole.Makesurestudentsplaceboth
pushpinsonthesamesideoftheirEarth.TellstudentsthattheEarthmoves
aroundthesuninanellipticalorbitandistiltedonitsaxis.ExplainthatasEarth
orbitsthesun,itrotatesonitsaxis,andtheaxisisalwayspointedinthesame
direction.HavethestudentsrepresentingtheEarthandsunineachgroupstand
approximately5-7feetapart.Dimorturnoffthelights.
4.Useguidedinquirytohavestudentsinvestigatedirectandindirectsunlight.
First,havethestudentactingasthesunkeeptheflashlightpointedstraightat
therepresentationofEarthwhilethestudentholdingEarthwalksinacircle
aroundthesun.TheEarthshouldstopwhenthepushpinrepresentingaperson
intheNorthernHemispherecan"see"thesun.AskthestudentholdingEarthto
tilttheEarthsothatthesun,withoutmovingtheflashlight,isshiningdirectly
overheadofthepushpin/personinthenorth.Ask:Isthesunmoredirectforthe
personatthetoporthepersonatthebottomoftheEarth?(top)Doyouthinkitis
warmerforthepersonatthetoporthepersonatthebottomoftheEarth?(top)
Whydoyouthinkso?Addressanystudentmisconceptions.Onecommon
studentmisconceptionisthatthisisduetotheNorthernHemispherebeing
closertothesun.Notethatthereisnosignificantdifferenceinthedistanceof
thesuntotheNorthernandSouthernHemispheres.Thedifferenceisdueto
directandindirectsolarradiation.Thehemispherethatispointedtowardthe
sunreceivesmoredirectsolarradiation,thusitiswarmer.Nowaskthestudent
holdingEarthtoorbitthesun,makingsuretoholdthetiltinthesamedirection
untilthetiltoftheEarthispositionedsothatthesunisdirectlyoverheadofthe
pushpin/personintheSouthernHemisphere.Ask:Isthesunmoredirect,or
bright,forthepersonintheNorthernHemisphereortheSouthernHemisphere?
(SouthernHemisphere)Whichpersondoyouthinkfeelswarmertemperatures?
(thepersonintheSouthernHemisphere)Why?(duetodirectsolarradiation)
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5.Useguidedinquirytohelpstudentsinvestigatetheroleofaxisandtiltin
thesun-Earthrelationship.
Whilethesunisstillshiningdirectlyoverheadofthepushpin/personinthe
SouthernHemisphere,havestudentslocatewhereintheclassroom,suchasa
wallorceiling,theNorthPolepointsto.Tapeablackcircletothewallatthat
locationtohelpstudentskeeptheaxispointedinonedirection.Next,askthe
Earthtoresumeorbitingthesun,whilekeepingtheNorthPolepointedatthe
blackcircle.RemindstudentstokeepthesunstationaryandpointedatEarth.
HavetherestofthegrouphelptomakesuretheEarth’stiltdoesn'tchange.
ExplaintostudentsthattheEarth'stiltdoesnotchangesignificantlyoverthe
courseofayear,butdoesshiftgraduallyovermillennia.Havestudentsstopthe
Earthafterone-halfofanorbitsothatitisoppositeofwhereitstarted.Then
askonegroupmembertomakeitdaytimeforthe“top”and“bottom”people.It
shouldbenightforthemiftheEarthhasorbitedcorrectly,sothestudentwill
havetospintheEarth.Finally,askgroupstomovetheEarthhalfanorbit
aroundthesunagain,makingsuretokeeptheNorthPolepointedattheblack
circle.Makesurethesundoesnotmove.Also,ensureastheEarthorbitsthe
sun,theaxisdoesnotchangeorientationandcontinuespointingtotheblack
circle.Haveagroupmembermakeitdaytimeforthe“top”and“bottom”
people.Ask:
DoesthesunshinemoredirectlyonthepersononthetophalfoftheEarth,or
thepersononthebottomhalf?(bottomhalf,orSouthernHemisphere)
Whichpersonfeelswarmertemperatures?(thepersonintheSouthern
Hemisphere)
Whichpersonisexperiencingsummer?(thepersonintheSouthern
Hemisphere)Winter?(thepersonintheNorthernHemisphere)Howdoyou
know?(ThepersonintheSouthernHemisphereisreceivingmoredirect
sunlight,soitiswarmerthereandisthesummerseason.)
Isthesunbrighterormoreconcentratedforthepersoninsummerorthe
personinwinter?(thepersoninsummer)
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6.Havestudentsmakeamathconnection.
Askforavolunteerfromoneofthegroupstocometothefrontofthe
classroomwiththeir“sun”(flashlight).Havetherestofthestudentssitonthe
floorinasmallareanearthecenteroftheclassroombutfacingthesun.Ask
studentstoimaginethattheflooristheNorthernHemisphereoftheEarth.In
thewinter,theNorthPoleoftheEarthispointingawayfromthesun,sothesun
appearsfarthersouthintheskytous.Havethestudentholdthesuncloserto
thefloor.Havetherestoftheclassplacetheirhandsclosetothefloorandpoint
towardthesun.Ask:Doyourfingerandthefloorformalargeorsmallangle?
(smallangle)Tellstudentstheyareforminganacuteangle.Thenhavethe
studentholdingthesunholditupashighasheorshecan.Havetherestofthe
classkeeptheirhandsclosetothefloorandagainpointtothesun.Ask:Isthe
angleyouhaveformedwithyourfingerandfloorlargerorsmaller?(larger)Tell
studentstheyareforminganobtuseangle.Ask:Whatseasondoesthis
represent?(summer)
7.Haveawhole-classdiscussionabouthowthesunaffectsEarth’sseasons.
Pointouttostudentsthattheseasonsareoppositeforpeopleonthetop(north)
oftheEarthandonthebottom(south)oftheEarth.Ask:
Whenitiswinteronthetop(north)oftheEarth,whatseasonisitonthe
bottom(south)oftheEarth?(summer)
Whenitiswinteronthebottom(south)oftheEarth,whatseasonisitonthe
top(north)oftheEarth?(summer)
Howcanweuseanglestohelpotherstounderstandseasons?(Inthesummer,
theangleofthesunismoredirectlyoverus,andlarger,providingmore
directsolarradiationandmakingitwarmer.Inthewinter,theangleofthe
sunissmallerandwereceivelessdirectsolarradiation,soitiscolder.)
TipGoingGreen
Tomakethisactivitymore"green,"useroundfruitinsteadofpolystyrenefoam
balls.
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Modification
Foradvancedstudents,introducetheconceptsofthewintersolstice,summer
solstice,autumnalequinox,andvernalequinox.Havethemmakeconnections
betweenthehands-onactivityandthesespecialdaysthatcorrespondto
differentpointsintheEarth'sorbit.
Modification
InStep4,addressanystudentmisconceptionsaboutdirectversusindirect
sunlight.Dimthelights.Adjustasmallflashlighttoitsmostconcentratedbeam
andshinethelightondarkpaperorawall.Explainthatthisissimilarto
concentrated,directsunlightduringsummermonths.Thenadjusttheflashlight
tothewidebeamanddescribeitasdispersed,orindirectsunlightduringwinter
months.
InformalAssessment
AskstudentstoorallyexplainhowtheinteractionbetweenthesunandEarth
affectsseasonshereonEarth,andwhathappenswiththesun'sraysduringthe
differentseasons.Encouragethemtousevocabularytermsaxis,tilt,direct
sunlight,andindirectsunlightintheirresponses.
ExtendingtheLearning
Explaintostudentsthateveryplanetinoursolarsystemhasseasons.Butthe
seasonsthatoccuronotherplanetsareextremelydifferentfromthetraditional
spring,summer,autumn,andwinterthatweexperienceonEarth.Remind
studentsthatthetworeasonsseasonsoccurarethetiltofaplanet’saxisandits
orbitaroundthesun.Ask:Aplanet’saxismighthaveasmallerorlargertiltthan
Earth’s.Whichwouldcausemoreextremeseasons—asmallerorlargertilt?
(larger)Aplanet’sorbitmightbeclosertoorfartherawayfromthesunthan
Earth.Whichwouldcausemoreextremeseasons—beingcloserorfartheraway?
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(closer)Havestudentsexplaintheiranswersusingevidencefromthehands-on
activity.ThenhavethemreadalistfromNASAaboutthelengthofseasonson
otherplanetsinoursolarsystem.
O BJECTIVES
Subjects&Disciplines
InformalEducation
AcademicEnrichment
Mathematics
Geometry
Science
Astronomy
Physicalsciences
Spacesciences
LearningObjectives
Studentswill:
explaintherelationshipbetweenthesunandEarth
describehowthetiltandpositionoftheEarthaffectstheseasons
explaindifferencesindirectandindirectsunlight
TeachingApproach
Learning-for-use
TeachingMethods
Cooperativelearning
Demonstrations
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Discussions
Hands-onlearning
Inquiry
Multimediainstruction
SkillsSummary
Thisactivitytargetsthefollowingskills:
21stCenturyStudentOutcomes
LearningandInnovationSkills
CommunicationandCollaboration
CriticalThinkingSkills
Analyzing
Applying
Understanding
NationalStandards,Principles,and
Practices
N C T M P RI N C I P LE S A N D S TA N DA RDS F O R S C H O O L
M AT H E M AT I C S
•Geometry(3-5)Standard4:
Usevisualization,spatialreasoning,andgeometricmodelingtosolveproblems
N AT I O N A L S C I E N C E E DU C AT I O N S TA N DA RDS
•(K-4)StandardB-2:
Positionandmotionofobjects
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•(K-4)StandardD-3:
Changesinearthandsky
I S T E S TA N DA RDS F O R S T U DE N T S (I S T E S TA N DA RDS *S )
•Standard2:
CommunicationandCollaboration
•Standard4:
CriticalThinking,ProblemSolving,andDecisionMaking
PREPARATIO N
WhatYou’llNeed
M AT E RI A LS YO U P RO V I DE
Blackconstructionpaper
Flashlights
Globe
Markers
Polystyrenefoamballsorroundfruit
Pushpins
Rulers
Scissors
Toothpicks
Transparenttape
RE Q U I RE D T E C H N O LO G Y
InternetAccess:Optional
TechSetup:1computerperclassroom,Projector,Speakers
Plug-Ins:Flash
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P H Y S I C A L S PA C E
Classroom
Home
SETUP
Beforestartingthisactivity,cutalarge,blackcircleoutofblackconstruction
paper.
G RO U P I N G
Large-groupinstruction
Small-groupinstruction
RE S O U RC E S P RO V I DE D: I M A G E S
Seasons
BACKGRO U ND & VO CABU L ARY
BackgroundInformation
Onecommonmisconceptionthatstudentshaveaboutseasonsisthatseasons
areduetohowcloseorfartheEarthistothesun.Thechangingpositionofthe
Earth’stiltisthereasonforthedifferencesintemperatureandlengthof
daylightthatdistinguishtheseasons.WhentheNorthernHemisphereofthe
Earthisleaningtowardthesun,itreceivesdirectsunlight.Thewarmthofdirect
rayscausesspringandthensummerinthatpartoftheglobe.Whenthe
NorthernHemisphereoftheEarthisleaningawayfromthesun,itreceives
moreindirectsunlight.Thecoolingeffectsofmoreindirectsunlightcause
autumnandwinter.BecauseoftheEarth’sapproximately23.5ºtilt,theseasons
intheNorthernandSouthernHemispheresarereversed,aboutsixmonths
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apartfromeachother.
PriorKnowledge
["theEarthorbitsthesunandrotatesonitsownaxis"]
RecommendedPriorActivities
None
Vocabulary
Term
Partof
acuteangle noun
angle
autumnal
equinox
noun
noun
axis
noun
Equator
noun
hemisphere noun
Northern
Hemisphere
NorthPole
obtuse
angle
noun
noun
noun
orbit
noun
season
noun
solar
radiation
Definition
Speech
noun
anglemeasuringbetween0and90degrees.
slantingspacebetweentwolinesthatultimatelymeetina
point.
autumnday,usuallyaroundSeptember22,whendayand
nightareofgenerallyequallength.
aninvisiblelinearoundwhichanobjectspins.
imaginarylinearoundtheEarth,anotherplanet,orstar
runningeast-west,0degreeslatitude.
halfofasphere,orball-shapedobject.
halfoftheEarthbetweentheNorthPoleandtheEquator.
fixedpointthat,alongwiththeSouthPole,formstheaxison
whichtheEarthspins.
anglemeasuringmorethan90degrees,butlessthan180
degrees.
pathofoneobjectaroundamoremassiveobject.
periodoftheyeardistinguishedbyspecialclimatic
conditions.
lightandheatfromthesun.
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Term
Southern
Hemisphere
Partof
noun
SouthPole noun
summer
solstice
vernal
equinox
winter
solstice
halfoftheEarthbetweentheSouthPoleandtheEquator.
fixedpointthat,alongwiththeNorthPole,formstheaxison
whichtheEarthspins.
dayoftheyearwiththemosthoursofsunlight,June20or
noun
21intheNorthernHemisphereandDecember21or22in
theSouthernHemisphere.
temperaturenoun
tilt
Definition
Speech
verb
noun
degreeofhotnessorcoldnessmeasuredbyathermometer
withanumericalscale.
toleanorslant.
day,usuallyaroundMarch21,whendayandnightareof
generallyequallength.Alsocalledthespringequinox.
(December22intheNorthernHemisphere,June22inthe
noun
SouthernHemisphere)longestnightoftheyearandthe
beginningofwinter.
ForFurtherExploration
Websites
NASA:EducatorFeatures—PlanetarySeasons
NationalGeographicScience:Space
NASA:SolarSystemExploration—Kids
NatGeoMovies:WildestWeatherintheSolarSystem
FU NDER
©1996–2017NationalGeographicSociety.Allrightsreserved.
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