TEACHER GUIDE - StarDate Online

TEACHER GUIDE

Get Close to McDonald ObservatoryLive and in PersonMcDonald Observatory offers a unique settingfor teacher workshops: the Observatoryand Visitors Center in the Davis Mountainsof West Texas. The workshops offer inquirybasedactivities aligned with national andTexas science and math standards. Teacherscan practice their new astronomy skills underthe dark West Texas skies, and partner withtrained and nationally recognized astronomyeducators.mcdonaldobservatory.org/teachers/profdevLive for StudentsThe Frank N. Bash Visitors Center featuresa full classroom, 90-seat theater, astronomypark with telescopes, and an exhibit hallfor groups of 12 to 100 students. Theseprograms offer hands-on, inquiry-based activitiesin an engaging environment, providingan informal extension to classroom andscience instruction. Reservations are recommendedat least six weeks in advance.mcdonaldobservatory.org/teachers/visitLive on VideoVisit McDonald Observatory from the classroomthrough an interactive videoconferenceprogram, “Live! From McDonald Observatory.”The live 50-minute program is designedfor Texas classrooms, with versions for grades3-5, 6-8, and 9-12. Each program is alignedwith Texas education standards.mcdonaldobservatory.org/lfmoFor complete details432-426-3640mcdonaldobservatory.org/teachersDamond Benningfield; Frank Cianciolo (inset)

Table of ContentsTEACHER GUIDETo the Teacher 4Resources 385th EditionEXECUTIVE EDITOReDITORart DIRECTORCURRICULUM SPECIALISTSCIRCULATION MANAGERDIRECTOR,PUBLIC INFORMATIONStaffDamond BenningfieldRebecca JohnsonTim JonesDr. Mary Kay Hemenwaykyle FrickeBrad ArmoskyPaul PreviteSandra PrestonSpecial thanks to all the teachers who evaluated this guide.Front CoverA Hubble Space Telescopeview of a swathof the Coma Cluster, acollection of thousandsof galaxies. Astronomersare studyingComa to learn aboutthe evolution of galaxiesin clusters.Back CoverWith Earth looming in the background, astronautsservice Hubble Space Telescope in thecargo bay of space shuttle Discovery.Support for Program numberHST-EO-10861.35-A wasprovided by NASA through agrant from the Space TelescopeScience Institute, which is operatedby the Association of Universitiesfor Research in Astronomy, Incorporated,under NASA contract NAS5-26555.The StarDate/Universo Teacher Guide is published by the McDonaldObservatory Education and Outreach Office, 2609 University Ave.#3.118, Austin, TX 78712. © 2008 The University of Texas at Austin.Direct all correspondence to StarDate, 2609 University Ave. #3.118,Austin, TX 78712, or call 512-471-5285. POSTMASTER: Send changeof address to StarDate, The University of Texas at Austin, 1 UniversityStation, A2100, Austin, TX 78712. Periodicals Postage Paid at Austin,TX. StarDate and Universo are trademarks of the University of TexasMcDonald Observatory.NASA/STScI/Coma HST ACS Treasury TeamClassroom ActivitiesShadow Play 6Modeling the Night Sky 8Observing the Moon 11Planet Tours 14Solar System Science 15Rock Cycle 16Equatorial Sundial 18Scale Models 20Sunspots 22Spectroscope 24Stars and Galaxies 28Coma Cluster of Galaxies 30Grades 5-8 Grades K-4Grades 9-12Visit StarDate Online at stardate.organd Universo Online at radiouniverso.orgS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 3

To the TeacherStarDate and Universo are dailyradio programs that transportlisteners into the universe.Many of the programs point outinteresting events or objects inthe night sky, with details on theunderlying science. Other programscover the history of astronomy andspace exploration, upcoming missions,recent discoveries, and relatedtopics.Radio stations receive the programson monthly compact disks, and thesesame monthly CDs are made availableto teachers around the country.Hundreds of teachers incorporatethe programs into their classroominstruction.The StarDate/Universo TeacherGuide can help you integrate Star-Date and Universo programs intoyour daily classes. We have providedsimple activities for several grade levels,most of which require no elaborateequipment. These activities areexamples upon which to build similarlessons based on current StarDateand Universo episodes. You can integrateand apply new skills from othersubject areas as you broaden students’awareness of astronomy.A transcript of a related StarDateradio program accompanies mostactivities. The scripts are boxed anddenoted by a small radio transmitterlogo. The scripts show the breadthNational Science Education Standardsof the radio program content whileproviding some idea of how theseand similar programs may be incorporatedinto lesson plans.StarDate and Universo provideadditional resources throughWorld Wide Web sites in bothEnglish and Spanish. These sitesprovide extensive informationon the solar system, stars,galaxies, and other sciencetopics, as wellas daily, weekly, andmonthly skywatchingtips. Web addresses forthese and other sitesare provided at the backof this publication.We occasionally produceprinted guides, posters, or otherresources as well. These resourcesare distributed to theteachers who receive theaudio CDs.StarDate/Universoand YourClassroomEach CD contains a fullmonth of either StarDateor Universo programming.You can integrate the informationfrom the programs into daily learningexperiences in your classroom ina variety of ways. You are free to copythe CDs for educational uses. CopiesEach activity in the StarDate/Universo Teacher Guide meets the NationalScience Education Standards (NSES), which were developed with theseguiding principles:• Science is for ALL students.• Learning science is an active process.• School science reflects traditions of contemporary science.• Improving science is part of systemic education reform.The NSES promote not just hands-on science, but also minds-on science.The astronomy context of these activities aligns their content with theNSES “Physical Science” and “Earth and Space Science” standards. The“Science as Inquiry” standards manifest in the structure and format ofthe activities. Some activities overlap grade levels; many teachers willfind ways to modify the activities to fit the level of their students.may be distributed to other teachers,placed in your school’s library, orused for other educationalpurposes. However,the copies may notbe sold or otherwisedistributed for noneducationaluses.Listening SkillsStarDate and Universoprovide an opportunityfor students to improve theirlistening skills. Teachers whopreview the daily programmay ask questionsabout the program tohelp students focuson the topic. Writtenscripts are availableon-line each daythrough the Star-Date Online and UniversoOnline web sites.Some teachers broadcast theprogram over the school intercomeach day.Note-Taking and DiscussionTo go beyond passive listening,have your students take notes. Someteachers have found that students aremore prepared to discuss the topic ifthey listen, take notes, then listen asecond time to check their notes.Extending Class LessonsWith their emphasis on objects inthe sky, StarDate and Universo aregreat sources for homework assignments.For this reason, some teachersplay StarDate or Universo at the endof class as they make an assignment.• Students can keep observing logs torecord their observations throughoutthe year. Their StarDate or Universonotes prepare them to go outside andsketch what they see.• Create a resource station wherestudents file information they havegathered from the programs. Studentsmay file their own drawings,data, and papers as well. Keepingyour copies of the CDs and a CDplayer with earphones will allow studentsto listen individually to selectedprograms. Students may create a4 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

database of the information filed atthe resource station. Some teachersuse this station as a reference sourcefor assignments.Bilingual InstructionUniverso can help you meet theneeds of Spanish-speaking studentsor students who are learning Spanish.• Have Universo CDs available at alistening station. Use the programs tointroduce the lessons and vocabularyto bilingual students before the lessonin English.• Have students who need supportin Spanish listen to the programs toreview concepts taught in English.• Encourage Spanish students to listento Universo programs. The writtentext (in Spanish) may be printed forthem to follow. For some programs,students can check their comprehensionby listening to or reading theEnglish version of the program afterthey hear the Universo program.Cross-Curriculum ConnectionsYou can incorporateStarDate and Universointo many subjectareas, including:Language Arts andSocial Studies• Use the programson skylore to create interest inmythology and ancient civilizations.• Have students keep a StarDateor Universo journal with theirsummaries of the programs andanswers to the pre-listeningquestions. Journal entries mayconsist of phrases, sentences,paragraphs, or drawings toillustrate the core concept.• Encourage students tothink on a large scale.For example, in teachinga unit on Thoreau,ask them to consider thevastness of the universe,using the radio shows tospark abstract thought andprepare them for existentialliterature.• Use the scripts from theStarDate or Universo websites and material from Star-Date magazine as supplementalreading materials.• Encourage students to explore thehistorical context and relevance ofthe events and livesof the astronomersdescribed in StarDateand Universo programs.• Use the programs toexplore the culturalperspectives relatingto astronomy and toteach about the impactof celestialevents on culturaldevelopment.Mathematics• Students canuse graphs andcharts duringthe skywatchingactivitiesin this guide.They can applyconcepts ofproportion andpercentage asthey compare the sizes of planets orthe distances between planets withinour solar system.They canestimate timesand relative distances.• Older studentscan apply principlesof geometryand trigonometryas they explorethe angles andorientations ofplanets and satellitesor the positionof the Sun or Moon inthe sky throughout theday or year.Fine Arts• Encourage studentsto make drawings oftheir concepts relatedto the programs. Forexample, if the programis about sunsets,they can draw their idealsunset, which might lead into a discussionof the Sun’s color and why itappears redder at sunrise and sunset.Or, for a program about space flight,students might draw a spacecraft visitinganother planet or a comet.• Astronomy-related music has beenpopular for centuries. Your studentsmay be more familiar with John Williams’score for “Star Wars” thanHolst’s “The Planets,” but both piecescan be used as a trigger for combiningtheir ideas about astronomy withmusic.Individualized LearningBecause StarDate and Universo topicsrange from basic to more complexconcepts, you can use them with studentsof all ages and ability levels.• With a copy of the program’s script,students can highlight key conceptsand challenging words as they listento the program.• Have students visit StarDate Onlineor Universo Online as an enrichmentactivity. They can search the web sitefor answers to their astronomy questionsor read the daily FrequentlyAsked Question.S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 5

Shadow PlaySu n w atc h e r sUntil well into the last century, one ofthe most important people inthe pueblos of the southwestwas the Sunwatcher. Each day,he watched the Sun rise, usinghills or other objects to track its motionalong the horizon. His observationstold the tribe when to plant or harvestcrops, and when to conduct importantceremonies.The Sunwatchers may have beencarrying on a tradition established bysome of the ancestors of the pueblopeople — the Anasazi, a Navajoname that means “the ancient ones.”They built a large, well-ordered civilizationin the Four Corners region amillennium ago.Archaeological sites at several Anasazivillages suggest that they watchedthe Sun carefully. One example is theSun room in Hovenweep Castle, a ruinin southeastern Utah. Doorways andwindows in the room align with the sunseton the summer and winter solstices— when the Sun appears farthest northand south in the sky — and the equinoxes,when it’s half-way between.Nearby, a pair of buildings atopCajon Mesa apparently served as asolar calendar. Sunwatchers kept trackof the Sun’s motion from a series ofwindows. They also used the shadowsof the two buildings to determine thearrival of the solstices and equinoxes.The most famous Anasazi sunwatchingsites are in Chaco Canyon, innorthwestern New Mexico. In fact,quite a few people are visiting the canyonthis week to watch the sunrise onthe summer solstice.This is the transcript of a StarDate radio episode thataired June 19, 2001. Script by Damond Benningfield,©2001.Everyone and everything has a shadow. Shadows illustrate how threedimensionalobjects can be viewed in two dimensions. Youngerstudents can learn about the Sun’s relative motion in the sky as theyexperiment with shadows.Materials• Chalk• Outdoor drawing area• Lamp• Globe (a large globe is preferable)• Tape• Action figure (3 inches or smaller)ACTIVITY ONEBegin by asking, “Where is the Sunat noon?” Depending on theage of the child, responsesmight be “straight up,” “inthe sky,” “overhead,” or “inthe south.” Ask, “What is ashadow?” Accept responses.PreparationDivide the class into teams of two or three before going outside.ExperimentBegin in the morning. One member is to play “statue” — holding stillwhile the other team members trace the outlines of both the statue’s feetand shadow on the pavement. When all the tracings are completed, theentire class can examine them. Wait about 30–60 minutes, then ask the“statues” to return to their places (which is why they traced their feet) andhold the same position again.AnalysisWhat has changed?An s w e rStudents should notice that thelength and position of the shadowhave changed. Younger childrenmay think that the “statue”changed position. Ask them topredict where the shadow willbe in three hours. Repeat thetracings about once per houruntil the end of the school day.The shadows will grow progressivelyshorter in the morninguntil mid-day, after which they will grow longer. It is best to do the tracingsthroughout the school day. Note that the shadow never shortens enough todisappear, which means that the Sun doesn’t pass directly overhead at noon(unless you live between the tropics). Depending on the grade, students may6 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

measure the lengths of the shadows or even graph the length versus time ofday. Discuss the results.ACTIVITY TWOThis activity demonstrates the daily motion of Earth. We perceive the Sunas rising, crossing the daytime sky, and setting. It is actually Earth thatmoves.PreparationInside the classroom, arrange all the children in a circle around a lamp,which represents the Sun. The teacher should demonstrate and then askthe children to “spin.” (Young children prefer the term “spin” to “rotate”when thinking about Earth’s motion.)National Science Education Standards• Content Standard in K-4 EarthScience (Objects in the sky,Changes in Earth and sky)• Content Standard in K-4 Scienceas Inquiry (Abilities necessary todo scientific inquiry)DemonstrationTo find the proper direction, place your right hand over your heart (theposition for reciting the Pledge of Allegiance) and rotate in the directionthe fingers point. (As an extension, walk around the lamp to model Earth’sannual motion around the Sun. Don’t try to spin and walk at the sametime; it takes 365.25 spins to make a year!)AnalysisWhat has changed?An s w e rWhen children are facing the lamp, it is day. When they are facing awayfrom the lamp, it is night.ACTIVITY THREEPreparationInside the classroom, demonstrate the connection between the first twoactivities. First, tape the action figure onto the globe at your geographiclocation. Still using the lamp to represent the Sun, place the globe at least6 feet away from the lamp (ideally with the globe’s spin axis tilted relativeto the lamp to represent the current season, so it will be tilted awayfrom the lamp in the winter and toward it in the summer).Light bulbExperimentDarken the room and spin the globe so that everyone can see a changein the length and position of the figure’s shadow.AnalysisHow does the figure’s shadow compare to the childrens’ shadows outside?An s w e rThe behavior of the shadows should be similar. Spinning the globe counterclockwisewhen looking down on the north pole will show the proper movementof the shadow from west to east.ExtensionStudents draw pictures of why we have day and night.Students study how ancient people created stories about what causes dayand night.S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 7

Modeling the Night SkyNational Science Education Standards• Content Standard in K-4 Earthand Space Science (Changes inEarth and sky, Objects in the sky)• Content Standard in 5-8 Earthand Space Sciences (Earth in thesolar system)• Content Standard in K-4 PhysicalScience (Position and motion ofobjects)This activity extends “Shadow Play”(page 6) to include more solar systemobjects and to examine their motions.Although Ophiuchus (oh-fee-YOO'-kus) is nota traditional constellation of the zodiac, theSun passes through its borders in December.In one year, the Sun passes through 13constellations. In classical mythology, Ophiuchuswas known as the serpent bearer.PreparationEach individual or group needs one copy of the constellation strip on page9. The teacher needs individual constellation pictures and cards with thenames or pictures of the following objects: Sun, Earth, Mercury, Mars, andJupiter. Allow each group of 2-3 students to glue or tape the strips together,matching the letters on the edges of each strip, A:A, B:B, C:C, and D:D.That will form a loop with the constellations in this order: Gemini, Taurus,Aries, Pisces, Aquarius, Capricornus, Sagittarius, Ophiuchus, Scorpius,Libra, Virgo, Leo, and Cancer. Ask students if they recognize any of thepictures. Some students may wish to color the pictures.Activity 1Place the loop so that the pictures face inward. Distribute two small balls(such as clay or marbles). Ask the students to place one ball to representthe position of the Sun in relation to the constellations. Then ask themto place the other ball where they think Earth should be in relation to theSun and the constellations and to explain to their partners why they chosethat position. Ask the students to identify which side of Earth will be dayand which side will be night. When the Sun is “in” a certain constellation(that is, standing on Earth, if you had the ability to see stars in thedaytime, which constellation would be behind the Sun), what constellationis seen at midnight? Your interactions will depend upon the studentresponses. If they place Earth rather than the Sun in the center, ask themto explain. For now, accept all answers.Ancient peoples tracked which constellations appeared in the direction ofthe Sun. They usually watched the sky near sunrise. For this model, theSun is in the middle and Earth goes around it (counterclockwise as seenfrom the north pole). The stars are very distant compared to the Earth-Sundistance.Activity 2Cut each figure out of one strip and paste it on an individual card. Pass thecards out to 13 students, who stand in a circle facing inward. (For a smallgroup, post the cards on backs of chairs to make a circle.) Make sure theyfollow the same order as the loop. Choose one student to be theSun and stand in the middle of the circle. Allow anotherstudent to individually model Earth’s motionthroughout the year, recalling that the directionof rotation and revolution are the same.For Earth, one turn around the Sun takes oneyear. (Although rotation can be consideredsimultaneously, remember that Earth rotatesin 24 hours, and anyone who spins 365 timesas they “orbit” the Sun will become dizzy!) As anextension, you may wish to include Earth’s tilt. Choose aspot above Gemini on a distant wall to be Polaris and tell “Earth”to always bend in that direction as it orbits the Sun.Activity continued, Page 108 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

DCPISCES AQUARIUS CAPRICORNUSBACBADGemini Taurus AriesSAGITTARIUS OPHIUCHUS SCORPIUSLIBRAVirgo Leo CancerS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 9

Op h i u c h u s a n d Se r p e nsTwo constellations that don’tget a lot of respect are in thesouthwest this evening, abovethe Moon and the bright planetJupiter. One of them is slighted by anyonewho can name the 12 signs of thezodiac. The other was slighted by thepeople who established the constellationboundaries: they chopped out itsmiddle.The constellations are Ophiuchus,the serpent bearer, and Serpens, theserpent.Ophiuchus is one of the largest constellations.More important, it lies alongthe ecliptic — the Sun’s path across thesky. The constellations along this pathform the zodiac. But Ophiuchus isn’tincluded in the lineup, even though theSun spends more time inside its bordersthan in Scorpius, which is next door.Ophiuchus represents the founderof medicine. In myth, he was such agood healer that he even brought thedead back to life. That was reminiscentof the powers of a snake: It can kill,but it also rejuvenates itself every yearwhen it sheds its skin. So in the sky, thephysician is also known as the serpentbearer.Appropriately enough, he’s holdingon to Serpens. The serpent’s head isto the west of Ophiuchus, with the tailto the east — severed by the body ofOphiuchus.Serpens and Ophiuchus are well upin the southwest at nightfall. Look for thecrescent Moon quite low in the sky, withbrilliant Jupiter and the bright orangestar Antares to its upper left. Ophiuchusand Serpens stretch out above thisbright trio.This is the transcript of a StarDate radio episodethat aired September 17, 2007. Script by DamondBenningfield, ©2007.We see different stars at different times of year because Earth orbits(revolves around) the Sun. Some constellations are small, while others arelarge. The Sun appears to move from one constellation to another in as fewas 6 days or as many as 43.Add more celestial objects to your model by handing planet cards to morestudents. These objects orbit the Sun like Earth, but at different rates. Thisworks best if they come in one at a time, each with their own rate of orbitingthe Sun. The following table recommends some approximations to use,along with the exact values, for periods of revolution (the time it takesfor the object to revolve around the Sun one time). Distance scales arenot preserved in this activity. For example, tell the students that Mercuryorbits the Sun four times in one Earth year. So the person who representsMercury has to race around the Sun four times while Earth goes aroundonly once. Some students will count this out. For younger students, drawingthe circles on the floor helps them maintain the proper distances. Stopoccasionally to ask, “If you are on Earth, where or when can you see thatobject?” Add more or fewer objects depending upon the age of the group.For older students, model sunrise/sunset and ask what objects are visiblein the sky at various times of day (just after sunset or at midnight,for example) and in which constellations they appear. If you have alreadystudied phases of the Moon (see “Observing the Moon,” page 11), it canbe inserted into this model, orbiting Earth in about one month while Earthorbits the Sun in one year.Object Approximate period Actual periodMercury 1/4 year 0.24 year = 88 daysEarth 1 year 1 year = 365.25 daysMoon 1 month 27.3 daysMars 2 years 1.88 yearsJupiter 12 years 11.86 yearsEvaluate• The asteroid Ceres has a period of 4.6 years. Where would it go in thisscheme? (Answer: between Mars and Jupiter.)• Why did we not include Venus (0.61 year), Saturn (29.42 years), Uranus(83.75 years), or Neptune (163.73 years)? (Answer: 0.61 years wouldbe difficult to model and adding Venus would make it crowded. The otherplanets orbit so slowly that they would barely move!)• Place a plain piece of paper under the loop and sketch the number oforbits (or partial orbits) for Earth and two other objects.Teaching note: Although this activity does not indicate relative distances,it is correct that all of the planets orbit the Sun in approximately thesame plane. That is why we can limit ourselves to just the constellationsthat form one great circle on the celestial sphere.10 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

Observing the MoonDoes the Moon always look the same? Does its surface look differentat different times? What will your students say when you ask themthese questions?Many students are aware that the Moon goes through phases, butexcept for the “man in the Moon” — which many admit they have ahard time seeing — they probably haven’t thought about the surfaceof the Moon and how we view it from Earth. Some students may mentionthat the Moon changes colors. It actually doesn’t — the Moon’scolor changes due to the effects of our own atmosphere, not anythingintrinsic to the Moon.Materials• Clear skies• Notebook• Soft drawing pencil• Binoculars• Chart on page 13National Science Education Standards• Content Standard in K-4 Earth andSpace Science (Changes in Earthand sky, Objects in the sky)• Content Standard in 5-8 Earth andSpace Sciences (Earth in the solarsystem)• Content Standard in 5-8 Scienceas Inquiry (Abilities necessary todo scientific inquiry)PreparationFirst, figure out when you can see the Moon. Use the StarDate Sky Almanacor a calendar to find the Moon’s phase on the day you will carry outthis activity. The outdoor part of this activity requires good weather.In choosing a day, keep these tips in mind:• Although “new Moon” may seem to be the perfect phase for this activity,it really isn’t. “New Moon” means “no Moon.” During this phase, theMoon is in the sky all day, but it lies in the direction of the Sun and itsnight side is facing Earth. That means no lunar surface features will bevisible.• During full Moon, patterns of dark and light on its surface are easy todistinguish. That’s when the “maria” — smooth, almost crater-freeregions on the Moon — are easiest to see.• During crescent or quarter phases, the craters and mountains cast distinctshadows and become more noticeable.Once you know the Moon’s phase, the chart provided here will help youdecide the best time of day (or night!) for lunar viewing.Lunar eclipseJohn GianforteActivityDraw two 10-cm circles in your observing notebook. List the time, date,sky conditions, and location. Indicate the phase of the Moon within yourcircle. Now, sketch in the lightand dark areas. A soft pencilworks best. Some students like tosmudge their lines to show lightand dark. If you have binoculars,repeat the activity using them.Phase New First Quarter Full Last QuarterBinoculars will allow you to see alot more detail. At another phaseRise Sunrise Noon Sunset Midnight(at least five days later), repeat the Highest in Sky Noon Sunset Midnight Sunriseactivity.Set Sunset Midnight Sunrise NoonS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 11

Fu l l Ea r t hThe Moon is AWOL right now. It passesbetween Earth and the Sunearly tomorrow, so it’s hiddenin the Sun’s glare. And even ifthe Sun wasn’t in the way, therewouldn’t be much to see: It’s night onthe lunar hemisphere facing our way,so the entire disk is dark.Well, almost dark. The Sun is shiningon the far side of the Moon, so it’s notlighting up the side that faces Earth. Butthe side that does face Earth is gettingsome sunshine — reflected off of Earth.We can see this “earthshine” whenthere’s a crescent Moon in the sky,because it makes the dark portion of thelunar disk look like a gray phantom.Right now, the earthshine is at its mostintense. That’s because there’s a fullEarth in the lunar sky. Earth covers anarea more than 13 times greater thanthe Moon does. And on average, eachsquare mile of Earth’s surface reflectsmore than three times as much sunlightback into space. So a full Earth is about40 times brighter than a full Moon.While a full Moon always looks thesame, a full Earth is constantly changing.Anyone standing on the Moonwould see the entire surface of Earth asour planet turns on its axis. So they’dsee different continents and oceans,plus the unceasing motions of cloudsin the atmosphere. And since the sameside of the Moon always faces Earth,our planet would always appear inexactly the same spot in the sky — abright blue and white ball spinning inthe sunlight.This is the transcript of a StarDate radio episode thataired May 7, 2005. Script by Damond Benningfield,©2005.AnalysisCompare the naked-eye and binocular drawings done on the same date witheach other. What details are visible? Can you identify any features from thelunar map? Now compare the drawings from one date to the other.ExtensionFor an in-class activity, make craters by dropping marbles or pebbles into adeep basin of flour sprinkled with dry chocolate milk mix. You should getnice craters with elevated edges, and some with a series of splashed outmaterials centered on the crater. In a darkened room, shine a flashlightonto the cratered surface and show how the angle of the flashlight determinesthe length of the shadows. Students can research the surface of theMoon in the library or on the Internet.As a math extension, calculate the angle between the Sun and Moon fordifferent phases.For English, write a poem about the Moon.Above: Impact craters andvolcanic valleys on the lunarsurface.Right: An Apollo 15 astronautsalutes the flag.JAXA/NHK (top); NASA12 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

Learning the Lunar LandscapeBay of DewPlatoSea ofColdSeaof RainsAristarchusKeplerOceanofStormsCopernicusArchimedesSea ofVaporsSea ofSerenitySea ofTranquilitySea ofNectarTaruntiusSea ofCrisesSea ofFertilityLangrenusJPL/TIM JONESSea ofMoistureSea ofCloudsTychoS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 13

Planet ToursNational Science Education Standards• Content Standard in 5-8 Earth andSpace Science (Earth in the solarsystem)• Content Standard in 5-8 PhysicalScience (Properties of objects andmaterials)Mo o n a n d Ju p i t e rOn the scale of our everyday lives,Earth is a big place. It’s so big,in fact, that an airliner, flyingnonstop, would take about twodays to circle its equator. Butour planet is tiny compared to Jupiter,the giant of the solar system. It’s 11times bigger around than Earth is, sothat airliner would need about threeweeks to circle Jupiter’s equator.And the sights out the window wouldbe spectacular.Jupiter doesn’t have a solid surface,so you wouldn’t see any mountains,deserts, or oceans. But the Jovian atmosphereis filled with giant storms, andwith belts of clouds that race around theplanet at hundreds of miles an hour.To avoid turbulence, you’d have togo around the biggest storm systems.That could add days to the trip, though,because the storms can be as big asEarth. And they produce lightning boltsthat are hundreds of times as powerfulas those on Earth. At night, such blastsmight be visible for thousands of miles.Different chemicals in the atmosphereadd color to the clouds, so you’d seeshades of yellow, brown, and redmixed with the white clouds that’remade of water vapor.And if you’re afraid of heights, youwouldn’t want to look down: the cloudlayers atop the Jovian atmosphere arescores of miles thick, so it would be along way down.This is the transcript of a StarDate radio episodethat aired February 19, 2006. Script by DamondBenningfield, ©2006.Planning to take a vacation soon? Visit Phobos! Small and cozy, Phobosorbits the fourth planet from the Sun in less than eight hours.From your observation deck on Phobos, you will have a superb viewof Mars. You will see its mountains, polar ice caps, and the largest volcanoin the solar system. Call your cosmic travel agent today!Try this creative activity to help your students explore the solar systemin an imaginative manner.PreparationUse StarDate or Universo CDs or printed materials such as StarDate: TheSolar System or the StarDate/Universo websites to find information aboutsolar system objects. As an aid, provide some examples of real travel brochuresor websites with travel ads available for students to preview. Forsecondary classrooms, a good resource is Active Physics: Sports by ArthurEisenkraft (ISBN 1-891629-04-02).ActivityBreak the class into teams that will research one planetary body (if youhave a large number of teams, you can include some of the moons of thesolar system, or comets and asteroids). The students use the informationthey collect to create travel posters, brochures, or television or radio commercialsfor their object.Each project should include real facts about the solar system object, butmay use “far-out” features to form the basis of unusual recreation opportunities.When everyone is finished, each team presents its product to therest of the class.AssessmentDevelop a grading rubric for differentgrades, keeping in mind thestandards. In addition to “facts”about solar system objects, the rubricshould ascertain whether studentsuse physical data to make comparisons.Making comparisons is the keyto learning science in this activity.Some teachers may be comfortablewith allowing the students to designthe rubric for their class after theyhave started the project; others maywant to pass the rubric out at thebeginning of the assignment. Oneteacher had students make Power-Point presentations and gave extracredit for working some mythologyand images into the presentation.Future tourists may detour aroundJupiter’s Great Red Spot, a storm thatis larger than Earth.NASA14 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

Solar System ScienceIn this activity, students explore and compare planets in our solarsystem. Each student becomes the “ambassador” for a planet and preparesby researching their planet, then meets with other ambassadorsto form new mini-solar systems.MaterialsStarDate: The Solar System or other reference material on the solar system.ActivitySplit the class into small groups; each group researches one planet. Studentsin the group make a list showing the planet’s atmosphere, size, mass,distance from the Sun, geology and surface features, surface temperature,and moons. They also write a sentence describing something unique orstriking about their planet — an impression.National Science Education Standards• Content Standard in 5-8 Earthand Space Science (Earth in thesolar system)• Content Standard in 5-8 Scienceas Inquiry (Abilities necessary todo scientific inquiry)• Content Standard in 5-8 PhysicalScience (Properties of objectsand materials)Have one ambassador from each group join with ambassadors from othergroups. Each group need not have exactly the same planet mix, but thereshould not be duplicates of a planet within a solar-system group. Theambassadors interview each other to exchange information and impressions.Once they have shared their information, the ambassadors should considerhow they could organize themselves. Some might want to arrange themselvesin order of distance from the Sun. Others might notice that someplanets are small and rocky and others large and gaseous. “Solar systems”may invent several organization schemes. They will note interesting orunexpected planetary features. For instance, Olympus Mons, a “super volcano”on Mars, seems odd. Have each system report to the class.Hints: The results may vary if the mix of planets is different in each system.The teacher should help students sum up the results, notingsimilarities and differences among the schemes. Most planetaryscientists organize planets into two divisions: terrestrial (likeEarth) and Jovian (like Jupiter). Terrestrial planets are small androcky with few or no moons, and they are close to the Sun. Jovianplanets are gaseous giants with many moons, and are fartherfrom the Sun.ExtensionWhat planet or object should NASA choose for future humanexploration? Ask the “solar system” to choose a planet or moon.With pictures and text describing its features, design a spacesuitfor the visit. For instance, Jupiter poses a serious challenge — it’smostly high-pressure gas. What materials would the astronautneed to stay alive? How would the suit help the astronaut exploreJupiter? Would wings help?Compare planets in our solar system to new extrasolar planetsthat astronomers have discovered.The solar system is filled with amazingsights, including (from top), anavalanche beneath a Martian icecap, the surface of Saturn’s big moonTitan, and Saturn‘s bright rings.NASA (3)S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 15

Rock CyclePl a n e ta r y Th e r m o s tatEven on a winter day, our Earth is afairly warm, comfortable homefor life. That’s thanks in part tothe carbon dioxide in our air.Although it accounts for onlya tiny fraction of the atmosphere, itwarms our planet by about 50 degreesFahrenheit, and keeps Earth from turninginto a ball of ice.Carbon dioxide is called a greenhousegas. Like the glass in a greenhouse,it traps heat, in the form ofinfrared energy. So sunlight can comein, but much of the heat can’t get out.In the distant past, the atmospherecontained much more carbon dioxide.But rain washed most of it out of the air.It combined with other chemicals to formcarbonate rocks, such as limestone.Today, some carbon dioxide is pumpedback into the air by volcanoes.There’s also carbon dioxide in theatmospheres of our two closest planetaryneighbors, Venus and Mars.Mars may have undergone the sameprocess as Earth, with almost all of itscarbon dioxide now locked up in rocks.The Martian atmosphere is thin, so Marsis cold and desolate, and temperaturesnormally stay well below zero.On Venus, though, the carbon dioxideremained in the atmosphere. Today,Venus’s atmosphere is 90 times thickerthan Earth’s, and it’s made almostentirely of carbon dioxide, so the surfacetemperature is about 860 degreesFahrenheit.Only on Earth is the balance just rightto provide a comfortable home for life.This is the transcript of a StarDate radio episodethat aired February 22, 2000. Script by DamondBenningfield, ©1999.This activity combines the concept of Earth’s rock cycle with the characteristicsof other planets in the solar system. After learning aboutEarth’s rock cycle and the basic characteristics of objects in the solarsystem, students can consider how to extend this concept to otherobjects. The student’s goal is to create a rock cycle for each selectedsolar system object.PreparationFirst, as a class, students should agree on a course of action based on theirown driving questions. For instance:• Which objects probably have some sort of rock cycle?• What information about the object would relate to the rock cycle?• What are the available resources of information?• How should we as a class conduct our research and present our results?After their investigation, students must communicate their results to theirpeers. This involves not just presentation, but also discussion about thesupporting evidence fortheir rock cycle claims.As an extension, studentscan investigate thecase for Pluto and comeup with their own conclusion— what is Pluto?Materials• StarDate: The Solar System(or Universo Guíaexposure& erosiondel Sistema Solar)• Slide projector andslides (optional) METAMORPHIC• Internet access, computer,and browser(optional)Activityheat &pressureEarth’s Rock CycleSEDIMENTARYcooling &chemicalchangemeltingmeltingIGNEOUSexposure& erosionEngageBegin by reviewing the basics of Earth’s rock cycle. Then pose a questionabout other members of our solar system (not just planets): do they haverock cycles, too? Record students’ driving questions and discuss ways to goabout answering those questions. You may wish to reserve Pluto as a specialsolar system member for later investigation (see the Extend section).ExploreDivide students into small groups of four to six. Each group should investigatea different planet, depending on the result of the class brainstorm.StarDate: The Solar System will help students gather information aboutplanetary features that provide clues to the planet’s rock cycle. If studentshave trouble, help them consider Earth’s rock cycle and how it relates toTim Jones16 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

Earth’s features. Air and water erode rocks into sediments. Earth’s mantleheats buried rocks to make metamorphic rocks. Continents collide andraise mountains for water and air to erode.ExplainThe planets closest to the Sun (Mercury, Venus, Earth, and Mars) arerocky; they will most likely show evidence of a rock cycle. The gas giants(Jupiter, Saturn, Uranus, and Neptune) won’t. But these gas giants haverocky moons that can be investigated. For each solar system object, informationabout its surface features, agents of erosion, and geologic structureunder the crust will provide the major clues necessary to construct a possiblerock cycle. Check your school’s library for available resources. A wealthof information about the planets resides on StarDate Online. One effectiveway to organize the research is to break the class into research groups,with each focusing on one planet or moon.National Science Education Standards• Content Standard in 5-8 Scienceas Inquiry (Abilities necessary todo scientific inquiry, Understandingabout scientific inquiry)• Content Standard in 5-8 Earth andSpace Science (Earth in the solarsystem, Structure of Earth system)ExtendBreak the students into another set of groups with each member being anexpert on a different planet. These groups discuss some of the followingquestions:• What is Pluto? Is it a planet?• What about the gas giants — Jupiter, Saturn, Uranus, and Neptune?Instead of rock cycles, might they have gas cycles?• Consider what might happen if you could change the conditions on yourobject, such as adding liquid water to Mars or changing Earth’s atmosphere.Would these changes affect the rock cycles on these bodies?Rain, wind, rivers, and ocean tideserode surface rocks, washing materialinto the oceans to begin therock cycle anew (below). Volcanoeson Io (lower left), Earth (bottom),and other bodies deposit new rockson the surface.EvaluateAfter their investigation, each group presents its object’s rock cycle tothe class. During their presentation, students should point to particularfeatures of their planet as evidence that supports different phasesof their hypothetical rock cycle. This could be a presentation involvingposters or computer graphics. Or it could be something else a bit moreinteractive, such as a poem or song.NASA (2)NOAAS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 17

Equatorial SundialNational Science Education Standards• Content Standard in 5-8 Earth andSpace Science (Earth in the solarsystem)• Content Standard in 5-8 Scienceas Inquiry (Abilities necessary todo scientific inquiry)Egy p t i a n Sto n e h e n geSummer arrives in the northern hemispheretoday, as the Sun appearsfarthest north for the entire year.In centuries long past, skywatchersaround the world watched for thesolstice at special observatories — circlesof stones. The most famous is Stonehengein England, but circles of much smallerstones were found in the Americas, too.The oldest of these stone observatoriesmay have been built in southern Egypt,at a site called Nabta. It was used6,000 years ago, and perhaps even earlier— at least a thousand years beforeStonehenge.Anthropologist Fred Wendorf of SouthernMethodist University discovered thesite in 1973. Last year, studies by Wendorfand Colorado astronomer J. McKimMalville confirmed that Nabta had anastronomical function.Among other artifacts, the site containsa 12-foot-wide “calendar circle” of smallstones. Two pairs of stones stand acrossthe circle from each other. If you lookthrough the spaces between each pair,you’ll see the point where the Sun roseon the summer solstice thousands of yearsago. This alignment was important to thepeople who lived at Nabta because monsoonsbrought a few inches of rain to theregion soon after the solstice.Over the centuries, though, the rainsdried up and Nabta was abandoned.But the people of Nabta may have left alegacy. Their culture may have stimulatedthe formation of Egypt’s Old Kingdom— the civilization that built the greatpyramids.This is the transcript of a StarDate radio episode thataired June 22, 2003. Script by Damond Benningfield,©1998, 2003.One of astronomy’s first tools to measure the flow of time, a sundial issimply a stick that casts a shadow on a face marked with units of time.As Earth spins, the shadow sweeps across the face. There are manytypes of sundials; an equatorial sundial is easy to make and teaches fundamentalastronomical concepts. The face of the sundial represents theplane of Earth’s equator, and the stick represents Earth’s spin axis.PreparationFirst, find your latitude and longitude and an outdoor observing site in aclear (no shadows) area. Determine north (from a map, or by finding theNorth Star at night and marking its location). Assemble the equipment asdescribed below. Use a flashlight to demonstrate how to position and readthe sundial indoors before going outside.Materials and ConstructionEach student team needs a copy of page 19 and a drinking straw.Have the students cut out the Dial Face Template. Fold and glue the template,making sure the dial faces are lined up. Cut a cross in the center holewhere the straw will be snuggly inserted. Mark the straw using the latitudestrip as a guide. First mark the bottom of the straw at one end, then marka line corresponding to your latitude. Place the straw in the template holeat the line marking your latitude. The south face of the template shouldaim toward the bottom of the straw. Make sure the stick and template areperpendicular. The straw should fit snugly; tape it in place if necessary.ExperimentOn a sunny day, take the sundial outside. Set it on a flat horizontal surfacewith the bottom of the straw and the folded edge of the template bothresting on the ground. Aim the straw with the top pointing due north. (Ifdone correctly, the straw will point at the celestial north pole, where wesee the North Star at night.) Record the time on the sundial at least fourtimes in one day, with measurements at least an hour apart. Each time,also record the “clock” time for your date and location. Try this experimentduring different months.Analysis1. If the sundial time did not match clock time, explain why.2. Why does this sundial have front and back dial faces?Answers1. For each degree east or west of the center of your time zone (your longitudedifference from the center of the time zone), there is a correction of four minutes.Also, the Sun’s location in the sky changes with the seasons, and a correctionof up to about 15 minutes for the “equation of time” must be made. Readthe correction from the graph on page 19. Daylight Saving Time changes resultsby one hour.2. The shadow of the straw is cast on the north face from March 21 to September21, and the south face from September 21 to March 21. The plane of thetemplate is aligned with the celestial equator. The Sun is north of the celestialequator during the first period (spring and summer) and south of the celestialequator during the second (fall and winter).18 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

4105478Dial FaceTemplateLatitude StripNorth FaceSpring/Summer2 0E66W2 557483 0392111203 51260555045403530255 78493394 011211Finished Sundial4 55 02105 5396 0857W 66 EBottom20.0015.0010.00South FaceFall/Winterminutes5.000.00Jan Feb mar Apr may Jun Jul Aug Sep Oct Nov Dec-5.00-10.00-15.00Correction for the “Equation of Time”S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 19

Scale ModelsSo l a r EclipseThe Moon will cover up the Sun earlytomorrow, briefly turning day tonight. Unfortunately, though, it’llhappen while it’s already nighthere in the United States, sowe’ll miss out on the show.The event is a total solar eclipse. Ithappens thanks to a coincidence inthe way the solar system is laid out:Even though the Sun is about 400 timeswider than the Moon, it’s also about400 times farther away. So when thegeometry is just right, the Moon can justcover the solar disk.As the Sun disappears, the air getscooler, and the sky turns dark. TheSun’s hot but thin outer atmosphere,the corona, forms delicate streamersof light around the Moon. And the firstor last moment of sunlight can form a“diamond ring” — a thin ring of lightaround the Moon, with a bright burstwhere sunlight streams through canyonsor between mountains.The Moon’s orbit is tilted a little,so most months the Moon passes justabove or below the Sun, and there’s noeclipse. But two or more times a year,the Moon’s orbit lines up just right,creating an eclipse. Many eclipses arepartial, so the Moon appears to onlynick the Sun. But this month it goes rightacross the heart of the Sun, creating abeautiful eclipse.The total eclipse is visible along athin path that runs through China andRussia, across the tip of northern Greenland,and just into Canada. The partialeclipse is visible across a much widerarea, but it doesn’t include the U.S.This is the transcript of a StarDate radio episode thataired July 31, 2008. Script by Damond Benningfield,Copyright 2008.Without being informed of the expected product, the students willmake a Play-doh model of the Earth-Moon system, scaled to size anddistance. The facilitator will reveal the true identity of the system atthe conclusion of the activity. During the construction phase, studentstry to guess what members of the solar system their model represents.Each group receives different amounts of Play-doh, with each groupassigned a color (red, blue, yellow, white). At the end, groups set uptheir models and inspect the models of other groups. They report patternsof scale that they notice; as the amount of Play-doh increases,for example, so do the size and distance of the model.MaterialsOn a central table for all to share• String• Rulers or meter sticks• Scissors (optional)For each group• One or more cans of Play-doh. All the Play-doh for a group should be thesame color.• Large paper sheet as a work surface for rolling and shaping the Play-dohPreparationColor code each amount of Play-doh: red, 2 cans; blue, 1.5 cans; yellow, 1can; white, 0.5 can. Divide students into groups of two to four members.Lay out materials for all groups to share in a central location. DistributePlay-doh and one large piece of paper to each group.ActivityIntroduce the problemTell the groups that they will make a scale model of two members of oursolar system. Do not reveal that it is the Earth and Moon — that’s the surprisethat makes this activity memorable. Along the way, they can makeguesses about what the model represents.Divide the Play-dohTell groups to divide their Play-doh into five equal pieces.They may use whatever creative and clever means they can think of tosolve this problem. Example solution: Roll the Play-doh into a long cylinder,then divide it into pieces. A 50-cm cylinder can be cut into 10-cmlengths, then formed into spheres. Tell groups to divide up one of the largerpieces into 10 equal size pieces; set one of these smaller pieces aside.Create two carefully sized piecesTell each group to mash everything together (except the one small piecepreviously set aside) into one big sphere. Roll the remaining small pieceinto a little sphere.20 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

SunspotsRe ve rse d Po l a r i t yWhen a character in TV science fictionfaces a tough technical problem,one solution always seemsto work: reverse the polarity.That may not fix problems inreal life, but for the scientists who studythe Sun, reversing the polarity is a bigevent. It signals that the Sun has starteda new 11-year cycle of magnetic activity.A new cycle began in January, whentelescopes on the ground and in orbitmeasured a small sunspot — a relativelycool, dark magnetic “storm” onthe surface of the Sun. The observationsshowed that the polarity of the sunspotwas reversed from that of the sunspotbefore it.As the Sun spins on its axis, differentlayers of hot gas spin at different rates.That generates a powerful magneticfield around the Sun.Over a period of several years, thelines of magnetic force get twisted andtangled. That produces many moresunspots. The lines can also cross eachother, creating “short circuits” — powerfulexplosions of energy and particles.These outbursts can disrupt communicationsand electrical systems on Earth.At the end of a cycle, the Sun’s magneticfield flips over: magnetic northbecomes magnetic south, and viceversa.The Sun has been quiet for the lastfew years. But the start of a new cyclemeans that it’ll get busier in the yearsahead. The new cycle should peakaround 2012, and end around 2019— when scientists will once again bewaiting for the Sun to reverse polarity.The Sun is a huge sphere of gas. The visible layer of the Sun, whichwe view as the surface, is the photosphere. Its temperature is about6,200 degrees Celsius (10,340 degrees Fahrenheit). Above the surfaceare the chromosphere and corona. Sunspots are some of the mostnoticeable features of the Sun.Materials• Telescope (with finder covered)• Piece of white cardboard mounted on atripodPreparationThe easiest way to position the telescope(since the finder is covered and you don’t want to“sight” along the side) is to move the telescope untilits shadow is smallest. If your telescope doesn’t havea special motor, the image will slowly track acrossthe cardboard as Earth rotates. You may use binoculars, although toomuch sunlight can cause heat to build up inside the binoculars and damagethem. For binoculars, the standard size (7x35) works satisfactorily.ExperimentDraw a circle around the edge of the Sun on some paper placed overthe cardboard. Now quickly sketch the positions and sizes of all the visiblesunspots. Write the time and date on the edge of the paper. Repeatyour observations over several days or weeks. (If you trace the images onvery thin paper, you can later overlap them to see changes.) Be careful toinclude the fine detail that surrounds some sunspots. An alternative is todownload images from web sites each day to use for this activity or to compareto your own data.Analysis1. Can you identify any sunspots or sunspot groups? Did they changeshape, size, or position over time?2. If you move the cardboard screen farther away, what happens to theimage?3. (Advanced) The diameter of the Sun is about 1.4 million km (864,000miles). Measure the diameter of your image and estimate the physical sizeof your largest sunspot. Earth is 12,700 km (7,900 miles). Compare yourlargest sunspot with the size of Earth. Find the size of the sunspot with aproportion equation:1,390,473 kmdiameter of Sun’s image in mm=sunspot diameter in kmsunspot image in mmThis is the transcript of a StarDate radio episode thataired June 13, 2008. Script by Damond Benningfield,©2008.4. Why are sunspots dark?22 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

!Safety WarningDo not look directly at the Sun,especially with a telescope. You canPERMANENTLY DAMAGE YOUREYES! When working with students,it’s best to cover the finder telescopecompletely so that they cannot lookthrough it. Never trust filters thatgo into the eyepiece or thatcover the objective.Answers1. Sunspots change size andshape over a period of days.The Sun rotates on its axis inabout 25 days (its equatorrotates faster than its poles).Observations taken over aperiod of several days shouldshow this.2. As you move the cardboardscreen back, the image becomesfainter and larger.National Science Education Standards• Content Standard in 9-12 Scienceas Inquiry (Abilities necessary todo scientific inquiry, Understandingabout scientific inquiry)3. Large sunspots can equal Earth in diameter.4. Do the following demonstration to illustrate that sunspots appear darksince they are cooler than the photosphere (they are about 4,500 degreesC/7,100 degrees F). Attach a dimmer switch or rheostat to a clear incandescentlight bulb. Place the bulb on its side on an overhead projector.With the projector on, focus the bulb so that the filament appears as asharp silhouette on the screen. Turn up the power until the filament glowsagainst the screen, then turn the power down until thefilament is just barely dark against the background.Turn off the projector and the bulb will seem toglow dimly by itself. Sunspots are only “dark”with respect to the hotter, brighter backgroundof the photosphere.Spanning more than 13 times the totalarea of Earth’s surface, this large group ofsunspots photographed in 2001 coincidedwith the peak of the 11-year solar cycle(see sunspot number chart below). Inset:Close-up view of a typical sunspot.300NOAO/NSFSUNSPOT NUMBER20010001900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000DATES t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 23

SpectroscopeElec tromagne tic Sp e c t r u mScientists learn much about the worldby splitting things apart. A geologistcan split rocks, a botanistcan split seeds, and a physicistcan split atoms. About the onlything an astronomer can split is a beamof light, but even that reveals a greatdeal — from the temperature of a starto the final moments of matter fallinginto a black hole.Our eyes perceive the light from astar as a single color. But instrumentssplit the light into its individual wavelengthsor colors. The intensity of eachwavelength tells astronomers how hotthe star is, what it’s made of, how it’smoving, and whether it has companions,like other stars or even planets.Visible light is just one of the formsof energy that make up the electromagneticspectrum. Other forms includeinfrared and radio waves, which havea longer wavelength than visible light,and ultraviolet, X-rays, and gammarays, which are shorter than light.Telescopes on the ground or in spacedetect these forms of energy and splitthem into their component wavelengths,too. Each type of energy tells us aboutthe environment in which it was created.Infrared, for example, comes fromrelatively cool objects like gas cloudsand planets. And X-rays come fromsome of the most violent objects in theuniverse, like disks of hot gas spiralinginto black holes.By splitting each form of energy,astronomers build a more completeunderstanding of the universe — onewavelength at a time.This is the transcript of a StarDate radio episode thataired in July 2004. Script by Damond Benningfield,©2001, 2004.Just as a geologist collects rocks or minerals and a botanist collectsplants, an astronomer collects light. Astronomers usually cannot touchthe objects they study, like stars or galaxies. But they can analyze thelight these celestial objects radiate using a spectroscope. When anastronomer looks at a star through a spectroscope, he or she sees acolorful spectrum that is full of information.Students will construct their own spectroscope as they explore andobserve spectra of familiar light sources. Extension activities expandtheir understanding of different kinds of spectra and sharpen theirobserving skills. You may challenge more advanced students to maketechnological improvements to their instruments.MaterialsFor class:• Incandescent light bulb (60-100-watt frosted) and base• String of clear holiday lights(optional)• Fluorescent light (single bulb)• Transmission grating sheet(available from science supply store)• 2 transparency sheets• Glo-Doodler(available from Colorforms)PreparationMaking the transmission grating cards1. Cut a 3x5-inch index card in half, resulting in two 3x2.5-inch cards.Then cut a narrow strip off the three inch side of one of the halves. Thiswill help fasten the card onto the spectroscope tube.2. Fold each 3x2.5-inch card in half along the short side, then snip a slitperpendicular to the fold about half a centimeter from either corner ofthe fold. Punch a hole about two centimeters down in the fold. The openingshould be about a centimeter wide.Preparing the grating1. Sandwich the transmissiongrating material between twosheets of transparency material.Try not to touch the verysensitive grating with yourfingers.2. Cut the “sandwich” into 1x2-cm pieces.For each spectroscope:• Half of a manila folder• Sheet of black paper• 3 index cards (3x5-inch size)• Tape or rubber bands• Scissors• A small paper clip• Hole puncher3 in2.5 in3. Tape it into place over the viewing hole on the index card along theedges. Do not put tape OVER the hole or small slit.paperclipslitpunchedholes24 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

National Science Education StandardsspectrumActivitysandwichspectrumEngageDistribute individual grating cards to the students. Let them look aroundthe room. You may wish to have a light bulb (e.g. 60- 100-watt frostedbulb) or string of holiday lights available.ExploreWith gratings in hand, ask students to look at an incandescent lightsource (light bulb with a filament) through the grating while holding itclose to their eye.• Content Standard in 9-12 PhysicalScience (Interactions of energyand matter)• Content Standard in 9-12 Earthand Space Science (Origin andevolution of the universe)• Content Standard in 9-12 Scienceand Technology (Abilities oftechnical design)Ask students• Where does the spectrum appear?Spectra appear to the right and left of the light source.• What is the color order?Violet is closest to the light source and red is most distant.• What could be done to improve the appearance or view of the spectrum?Darken the room.The grating is part of a spectroscope. As the students noticed, spectra arebest viewed against a dark background. Ask for alternatives to darkeningthe room. If necessary, hint at something hand-held, since this instrumentshould be portable. If no one mentions it, suggest that a tube, with the gratingfixed at one end, will block stray light from the view of the spectrum andprovide the structural support for the spectroscope components.What could you use to block out the stray light to make a dark backgroundfor viewing spectra?Paper ClipAttach the grating to one end of a tube. Cut a manila folder in half alongthe fold. Place a black sheet of construction paper on top of the manilafolder half. Roll them together along the long side so that the black paperlines the inside of the tube. Secure with rubber bands or tape.Attach the grating card to the tube (see figure, right). Fasten a paper clipto one end of the tube, leaving a bit of the clip end over the tube edge. Fastenthe grating card to the paper clip and secure with a folded card strip.Have the students look at the incandescent bulb through the tube (withthe grating end next to the eye). The tube should aim directly at the bulb;the students may need to move their heads to one side to see the spectrum.Turn off the incandescent bulb and turn on a single fluorescentbulb. Does the spectrum of the fluorescent bulb look like that of theincandescent bulb? What is the same or different? (Students should seea continuous spread of color in both bulbs’ spectra. They also may seeseparate bands of color only in the fluorescent bulb spectrum.)Grating cardFoldedStripFinished spectroscopeS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 25

Cover up part of the fluorescent light bulb so that a narrow slit of light isseen. Try making a slit in a double-thick manila folder and holding it infront of the fluorescent source. Compare the incandescent light and thefluorescent light. Do you see color bands now in one of the lights? Whichone?Color bands appear dimmer and thinner with the slit in place for the fluorescentbulb. The incandescent bulb has no bands.Which observing method renders the best detail view of the spectrum feature— with or without the slit?With the slit. There is a limit — if the slit is too narrow, the spectrum appearstoo faint.Where is a better place to put the slit, so that an observer can view otherlight sources?At the opposite end of the tube.Make an adjustable slit from two index cards. Cut identical rectangularslots, about 1x3 cm, into the center of two index cards. Stack the cardsthen fold both cards together along both long sides. The cardsshould now slide across each other. Adjust the size of the slitby sliding one slot over the other.Hold the adjustable slit at the opposite end of the tube fromthe grating and open and close it until you find a position thatshows detail and still allows enough light through to see thespectrum clearly. Rotate it if necessary so that the spectrumhas its largest height. This insures the parallel grooves in the grating runin the same direction as the slit.Congratulations! You have constructed a working spectroscope.ExplainThis is a transmission grating. Its surface is scored or etched with thousandsof parallel grooves per centimeter. As light travels through the narrowgrooves, diffraction effectively turns each groove into a new sourceof light. As the light spreads out, it interacts or interferes with light of thesame wavelength from other grooves. Sometimes the light waves reinforceeach other (constructive interference), other times they cancel out andbecome invisible (destructive interference). Collectively, the constructiveinterference pattern directs a particular color along a unique angle fromthe grating. The result is a color spectrum. That’s why blue light appearsclosest to the image of the source, while red is farthest away. Along thoseangles, the constructive interference for that color lines up.The tube blocks stray light that washes out details in the spectrum.Against the dark background, subtle details of the spectrum are easilyseen. It also acts as a structure to attach the grating. The slit allows thewavelengths (colors) of light to be resolved. The diffraction grating isallowing you to see images of the slit side by side. The narrower the slit,the more detail you can see. For instance, a narrow slit may resolve a pairof lines in what appeared as a single emission feature viewed through a26 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

wide slit. But as the slit narrows, less light passes through. So an observermust strike a balance between the spectrum’s resolution and brightness.The incandescent light has a hot filament which produces a continuousspectrum (hot liquids also produce continuous spectra). The fluorescentlight is made of a tube of hot gas which produces an emission spectrum— more energy is released at certain wavelengths than at others so thosecolors are more distinct. Which wavelengths are produced depends uponthe nature of the gas within a tube. Each gas has its own “fingerprint” orpattern of wavelengths. In a fluorescent light, the gas is mercury.Technical notes forchemistry/physics teachers•This activity fits well with yourexploration of atomic structure,spectra of various elements, howspectra vary for isotopes, andKirchhoff’s laws.[For some grade levels, the above explanation is too technical; the teacher maywish to demonstrate constructive and destructive interference with waterwaves.]ExtendTurn on the incandescent light and hold up the Glo-Doodler in front of it.Ask students to describe how this spectrum is different from that of thebulb by itself or from the fluorescent bulb. (The Glo-Doodler absorbs certainwavelengths, which show as black bands in the spectrum.)Think of a safe way to view the spectrum of the Sun — DON’T LOOK ATTHE SUN DIRECTLY!! For instance, point the spectroscope at brightly litclouds or the full Moon (which shines by reflected sunlight). What type ofspectrum does the Sun produce? (The Sun produces an absorption spectrum.The Sun’s photosphere, the solar layer where the Sun radiates mostof its light, is cooler than deeper solar layers. The hotter, deeper layers ofthe Sun act like the light bulb filament while the photosphere acts like theGlo-Doodler. Atomic elements in the photosphere selectively absorb certainwavelengths of light. The resulting spectrum shows the absorbed wavelengthsas diminished bands, or lines, as astronomers call them.)Scientists use spectroscopes to safely explore any heated object, from thesurface of the Sun to a chemical heated by a flame. How could a scientistdetermine what elements may exist in the Sun’s photosphere? What processwould you suggest?The spectroscope that the students construct in this activity does not allowfor direct measurement of wavelengths. Based on their knowledge of spectroscopeconstruction and their observations of spectra, ask students howthey would improve their spectroscope. Could it allow an observer to measurethe wavelength as they view a spectrum through the spectroscope?They should include a procedure for calibrating the wavelength scale.EvaluateGiven a diagram of a scientific spectrograph or spectroscope, identify themain parts: slit, tube, and grating or prism. Early spectroscopes used aprism instead of a grating.A portion of our Sun’s spectrum revealsdark lines representing specific elementspresent in the Sun’s atmosphere.NOAO/NSFS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 27

Stars and GalaxiesSe e i n g i nto t h e Pa s tWe can’t travel into the past, but wecan get a glimpse of it. Everytime we look at the Moon, forexample, we see it as it was alittle more than a second ago.That’s because sunlight reflected fromthe Moon’s surface takes a little morethan a second to reach Earth. We seethe Sun as it looked about eight minutesago, and the other stars as they were afew years to a few centuries ago.And then there’s M31, the Andromedagalaxy — the most distant objectthat’s readily visible to human eyes.This great amalgamation of stars standsalmost directly overhead late this evening.When viewed from a dark skywatchinglocation, far from city lights,it looks like a faint, fuzzy blob. But thatblob is the combined glow of hundredsof billions of stars — seen as it lookedmore than two million years ago.Andromeda is like a larger version ofour own Milky Way galaxy. It’s a flatdisk that spans more than a quarter-millionlight-years. Its brightest stars formspiral arms that make the galaxy looklike a pinwheel. Yet the galaxy is sofar away that its structure is visible onlythrough telescopes.The light from M31 has to travelabout two and a half million light-yearsto reach us — about 15 quintillionmiles — the number 15 followed by18 zeroes. Yet even across such anenormous gulf, the galaxy is so brightthat we can see it — faintly — with ourown eyes, crossing high overhead latetonight.Student PageA galaxy is a gravitationally bound system of stars, gas, and dust. Galaxiesrange in diameter from a few thousand to a few hundred thousandlight-years. Each galaxy contains billions (10 9 ) or trillions (10 12 )of stars. In this activity, you will apply concepts of scale to grasp thedistances between stars and galaxies. You will use this understandingto elaborate on the question, Do galaxies collide?ExploreOn a clear, dark night, you can see hundreds of bright stars. The next tableshows some of the brightest stars with their diameters and distances fromthe Sun. Use a calculator to determine the scaled distance to each star(how many times you could fit the star between itself and the Sun). Hint:you first need to convert light-years and solar diameters into meters. Onelight-year equals 9.46 x 10 15 meters, and the Sun’s diameter is 1.4 x 10 9meters.Star(Constellation)Diameter(Sun=1)Distance(light-years)Spica (Virgo) 8 261Betelgeuse (Orion) 600 489Deneb (Cygnus) 200 1,402Altair (Aquila) 2 17Vega (Lyra) 2.7 26Sirius (Canis Major) 1.6 8.6Scaled Distance(distance÷diameter)There are three galaxies beyond the Milky Way that you can see withoutoptical aid: the Andromeda galaxy, the Small Magellanic Cloud, and theLarge Magellanic Cloud. Figure the scaled distance to these galaxies (howmany times you could fit the galaxy between itself and the Milky Way).GalaxyDiameter(light-years)Distance(light-years)Milky Way 100,000 0Andromeda Galaxy 125,000 2,500,000Large Magellanic Cloud 31,000 165,000Small Magellanic Cloud 16,000 200,000Scaled Distance(distance÷diameter)(no conversion needed)This is the transcript of a StarDate radio episodethat aired October 14, 2006. Script by DamondBenningfield, ©2006.ExplainHow does the scaled distance of galaxies compare to stars?ElaborateDo you think galaxies collide? Why or why not?28 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

Teacher Lesson KeyObjectives• Calculate scale distances of stars and galaxies.• Compare neighboring galaxies to neighboring stars.• Understand the relative distances between objects in space.EngageFind a round object in the classroom that is about 2 to 5 inches in circumference(such as a water bottle, tennis ball, or soda can). We will use a tennisball as an example. Using a table that everyone can see, ask the students,“How many tennis balls would it take to go from one end of this table to theother? In other words, how many tennis balls across is the table?” Accept allanswers. Then find the answer in front of the class by moving the ball acrossthe table one space at a time, counting each move out loud.Explore (Answers)National Science Education Standards• Content Standard in 9-12 Scienceas Inquiry (Understanding aboutscientific inquiry)• Content Standard in 9-12 Earthand Space Science (Origin andevolution of the universe)StarsScaled DistanceTo convertGalaxiesDistance÷DiameterDistance (ly) x 9.46 x 10 15 (m/ly) (both must be in the same units, Distance÷DiameterDiameter (Suns) x 1.4 x 10 9 (m/Sun)do conversions first)(no conversion needed)Sirius (Canis Major) 3.59 x 10 7Spica (Virgo) 2.22 x 10 8Betelgeuse (Orion) 5.51 x 10 6Deneb (Cygnus) 4.74 x 10 7Altair (Aquila) 5.74 x 10 7Vega (Lyra) 6.51 x 10 7Scaled Distancefrom Milky WayDistance÷Diameter(no conversion needed)Milky Way ------Andromeda Galaxy 20Large Magellanic Cloud 5.32Small Magellanic Cloud 12.5ExplainHow does the scaled distance of galaxies compare to stars?Galaxies, compared to their size, are much closer together than stars. Neighboringstars are usually millions of star-diameters apart, while galaxies areusually less than 100 galaxy-diameters apart.ElaborateDo you think galaxies collide? Why or why not?Galaxies do collide. They are relatively close to each other and they have thecombined mass of billions of stars. So even over large distances, the attractionbetween galaxies can accelerate them toward each other. Thick of bowling balls(galaxies) versus sand grains (stars) on a trampoline (space). The galaxies stretchand distort the trampoline much more, and over a wider area, than do single stars.Even though galaxies collide, the stars within galaxies seldom collide becausethey are so far away from each other. Clouds of gas and dust in the galaxies docollide, though, giving birth to new stars.EvaluateRubric: Explore = 60 pts (6 pts for each calculation), Explain = 25 pts,Elaborate = 15 ptsS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 29

Coma Cluster of GalaxiesNational Science Education Standards• Content Standard in 9-12 Science asInquiry (Abilities necessary to do scientificinquiry, Understanding aboutscientific inquiry)• Content Standard in 9-12 Earth andSpace Science (Origin and evolutionof the universe)Invisible Clu s t e rIf you aim a big telescope at the ComaCluster, you’ll see galaxies galore— thousands of galaxies of all sizesand shapes, from little puffballs tobig, fuzzy footballs. Even so, you won’tsee most of the cluster because it’s invisibleto human eyes.Some of the cluster’s “dark side” is inthe form of superhot gas that glows in X-rays. All together, the gas is several timesas massive as the galaxies themselves.There’s a dynamic interplay betweenthe hot gas and the galaxies.As galaxies “fall” toward the center ofthe cluster, they fly through the hot gas,which strips away the cold gas insidethe galaxies. Without their cold gas, thegalaxies can’t give birth to new stars. Thathelps transform the appearance of someof the galaxies. Spiral galaxies lose theirspiral arms, so they look like featurelessdisks.But the galaxies may have an effect onthe hot gas, too. Over the eons, it shouldhave cooled, but it hasn’t. Hot “jets” ofparticles from the centers of some galaxiesmay act like big blowtorches, keepingthe gas hot.Yet even the gas and the galaxies combinedmake up only a small fraction of theComa Cluster. As much as 80 percent ofits mass may consist of dark matter — aform of matter that produces no detectableenergy, but that exerts a gravitational pullon the visible matter around it. The darkmatter ensures that most of this impressivecluster remains invisible.In 2006, Hubble Space Telescope aimed at a nearby collection ofgalaxies called the Coma Cluster. Using the HST images, astronomersgained fascinating insights into the evolution of galaxies in densegalactic neighborhoods. In this activity, students will first learn thebasics of galaxy classification and grouping, then use HST images todiscover the “morphology-density effect” and make hypotheses aboutits causes.Materials & Preparation• Each student needs a copy of the next 7 pages (not this page). You maycopy the pages out of this guide, but it is recommended that you go tomcdonaldobservatory.org/teachers/classroom and download the studentworksheets. The galaxy images in the online worksheets are “negatives”of the real images, which provides better detail when printing. Supplementalmaterials for this activity are also available on the website.• Each student or student team will need a calculator and a magnifyingglass (a linen tester works well).• Knowledge of percentages is needed before doing this activity.Suggested Grading• Page 31 (5 pts): Student provides clear explanations of the scheme.• Page 32 (2 pts total, 2 pts each): Answers: (E/S0/SB0 – 2,6,9), (S– 1,8,12), (SB – 3,4,10), (IR – 5,7,11)• Pages 34 and 35: Not graded; based on student’s subjective interpretation.• Page 36 (30 pts): Graded for completion, not accuracy. Students will getdifferent numbers, but math should be correct. Answers for percentagesare typically in the following range: (Cluster: E 50 percent, L 30 percent,S 20 percent) (Field: E 20 percent, L 10 percent, S 70 percent). Studentsusually find a higher percentage of spirals in the field.• Page 37 (bottom, 30 pts): Student hypothesis should mention theeffects of interactions and ram-pressure stripping in changing past gasrichspirals into current gas-poor ellipticals and lenticulars in clusters.This is the transcript of a StarDate radio episode thataired May 6, 2008. Script by Damond Benningfield,©2008.30 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

GEMS COLLABORATIONEngageThe diagram above shows a mosaic of40 galaxies. These images were takenwith Hubble Space Telescope and showthe variety of shapes that galaxiescan assume. When astronomer EdwinHubble first started studying these varioustypes of galaxies in the 1920s, herealized he needed to develop a way toorganize and categorize them. He createda classification scheme in which hegrouped similar galaxies together. Yourjob is to do the same thing. In the chart,invent your own four galaxy types andprovide a description and three examplesfor each one.Galaxy Type(name and draw)Defining Characteristics(write a short description, provide enough detailso that anyone could use your scheme)Three Examples(give 3 gridcoordinates)S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 31

John Kormendy/Tim JonesELLIPTICAL GALAXIESBoxy Disky SBOORDINARY SPIRALSExploreThe image on the left is the classification scheme that Hubble himselfcame up with. He thought that the “tuning fork” sequence represented theevolutionary progression of galaxies. This concept turnedout to be wrong, although astronomers still use thesegeneral categories and labels to describe galaxies.The Main Galaxy TypesSOSb• Elliptical (E): Spherical or elliptical shape (likeSaSc Ima football), has no flat disc or spiral armsSBaSBbIBmSBc• Lenticular (S0): Smooth, flat disk shape withoutspiral structure, often hard to distinguishfrom ellipticals• Barred Lenticular (SB0): Same as above, but with anelongated (barred) nucleus• Spiral (S): Flat disk shape with notable spiral patterns inthe outer disk, also contains a large bright1 2 3central bulge• Barred Spiral (SB): A special type of spiralcharacterized by an elongated nucleus withthe spiral arms springing from the ends ofthe barBARRED SPIRALSIRREGULARS4 5 67 8 9There are two other categories for classifyinggalaxies:• Irregular (IR): An oddly shaped galaxythat doesn’t fit into any other category• Interacting (INT): Two or more galaxiesthat are so close together that they areaffecting each other’s shapeUsing the definitions above, place the 12 galaxieson the left into their proper morphologycategories:MorphologyPicture Numbers (3 each)ESO (top right); all others NASA10 11 12E/S0/SB0SSBIRThe smallest galaxies are often called dwarfgalaxies (No. 5 and No. 7 are dwarf galaxies).These contain only a few billion stars— a small number compared to the MilkyWay’s 200 billion. The largest ellipticals containseveral trillion stars.32 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

The Coma Galaxy ClusterThe Coma Cluster, which is centered about 320 million light-years away,contains several thousand individual galaxies. The cluster has a roughlyspherical shape and is about 20 million light-years across. (For comparison,the Milky Way is 100,000 light-years across). That many galaxiesin a relatively small space makes the Coma Cluster one of the richest anddensest galaxy clusters in our region of the universe.ArcturusCOMA BERENICESBIG DIPPEROn the following pages you will be asked to count differenttypes of galaxies. Use the labels on this picture as an exampleof how to count the various objects.I) Ellipticals or LenticularsIt can be hard to tell these apart. If you know it’s either anE or S0/SB0, it is okay toguess between these two.II) Spirals and Barred SpiralsIt can be hard to tell theseapart. If you know it’seither an S or SB, it is okayI ??to guess between these two.?III) Irregular galaxyIV) UncertainAn edge-on view of a galaxythat could possibly beIan S0, SB0, S, SB, or IR.There are too many possibilities,Starso do not countthese.Star)Any object that has“crosshairs” sticking out ofIit is a foreground star in theMilky Way galaxy, so do notcount these.IV IV I?)Don’t count small, faintStarobjects like these that areIItoo hard to classify.IIIIVWIIII?IIIII?NWStarIINASA/STScI/Coma HST ACS Treasury Team (3) Tim JonesS t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 33

ACount the number of galaxies of eachmorphological type and write down thenumber in the correct spot in the table.Use the guidelines on page 4 to help youdecide which objects to count.Top Image (A)Bottom Image (B)E S0 /SB0 S SB IR / INTB34 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

CTop Image (C)Bottom Image (D)E S0 /SB0 S SB IR / INTCount the number of galaxies of eachmorphological type and write down thenumber in the correct spot in the table.Use the guidelines on page 4 to helpyou decide which objects to count.DNASA/STScI/Coma HST ACS Treasury Team (4)S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 35

ExplainGalaxies in Clusters, Groups, and the FieldGalaxies are found throughout the universe, from our next door neighbors— the Magellanic Clouds and Andromeda — all the way out to the edgeof the visible universe 13 billion light years away. Nobody knows for sure,but it is estimated that there are 100 billion galaxies or more in the visibleuniverse, and many more beyond that. Galaxies live in a variety of environments.Sometimes large numbers of them are packed close together inclusters, such as the Coma Cluster; sometimes they gather in smaller numberscalled groups, like the Local Group that contains our Milky Way; andsometimes they are isolated far from one another in the field.Galaxy ClusterLarge and denseGalaxy GroupSmall and denseThe FieldLarge and desertedNumber ofGalaxiesMinimum Numberof Non-dwarfGalaxiesDiameter(1 Mpc = 3.26million light years)50 to thousands 6 2 to 10 Mpcless than 50 3 1 to 2 Mpcvery few 0Voids, can be largerthan 100 MpcTotal Mass10 14 to 10 15solar masses10 13 solarmasses< 10 10Clusters, groups, and some isolated galaxies can all be part of even largerstructures called superclusters. At the largest scales in the visible universe,superclusters are gathered into filaments and walls surrounding vastvoids, often described as resembling large soap bubbles. This structureoften is referred to as the “cosmic web.”On the previous two pages, the images on the top (A&C) show the densecentral core of the Coma Cluster, and the images on the bottom (B&D)show galaxies out in the field. Fill in the table below using the numbersyou wrote down on the previous two pages:Morphology→Image AImage CEEllipticalsS0 & SB0LenticularsS & SB (sum both together)Regular and Barred SpiralsTotal(E+S0+SB0+S+SB)Sum Total FromA + C (e) (f) (g) (h)Image BImage DSum Total FromB + D (i) (j) (k) (m)Using a calculator, find the percentagesof each galaxy type in the cluster versusthe field (ignore IRs and INTs). Fill ineach of the boxes on the right:— im j— m—m k Where did you find a higher percentage of spirals — in the Cluster or in the Field? Answer: __________________________36 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

The percentages that you just found tell us which types of galaxies arecommon in the Coma Cluster versus which types are common in the field.Astronomers have done this same exercise on hundreds of thousands ofgalaxies in the nearby universe, and discovered that the following percentagesare pretty typical:• In dense clusters, 40 percent of the galaxies are ellipticals, 50 percentare lenticulars, and 10 percent are spirals.• In the field, 10 percent of the galaxies are ellipticals, 10 percent are lenticulars,and 80 percent are spirals.When galaxies are found very close together there are more ellipticalsand lenticulars. When galaxies are far apart there are morespirals. Astronomers call this the “morphology-density effect” (the wordmorphology means “type” or “class,” not “transformation,” as in biology).The term basically means that in crowded galaxy neighborhoods, like clusters,there are different types of galaxies than are found in open areas, likethe field.ExtendThe clues needed to answer the last question are in the following paragraphs.Please read the paragraphs carefully and then answer the questionat the right.As a general rule, spiral galaxies (S and SB) have a lot of gas and are stillforming lots of new stars. Elliptical and lenticular galaxies (E, S0, and SB0)are gas poor and are not making many new stars.Spirals are Gas-richBoth Ellipticals and Lenticulars are Gas-poorGalaxies that are very close to each other, suchas those in clusters, often undergo many violentinteractions with each other. When a gas-richspiral galaxy interacts with another galaxy, ittends to quickly use up most of its gas to makenew stars, leaving little gas behind. Galaxy-galaxyinteractions often change gas-rich galaxies intogas-poor galaxies. Many lenticular galaxies are theremains of old spirals that have lost their gas, andmany elliptical galaxies are the remains of severalspiral galaxies that have collided.Galaxy clusters are usually filled with a lot ofextremely hot gas that is spread between galaxiesthroughout the cluster. However, there is no hotgas like this out in the field. When the radiationfrom this hot gas hits a spiral galaxy, it strips thespiral galaxy of its much cooler gas in a processcalled ram-pressure stripping. This process quicklyconverts a gas-rich spiral galaxy into a gas-poorlenticular galaxy. Spiral galaxies have a hard timesurviving in the superheated gas environment.Using what you’ve learned, write a hypothesis that might explain why we seethe morphology-density effect. In other words, why do we see more ellipticaland lenticular galaxies in clusters and more spiral galaxies in the field? Rememberthat galaxies change and evolve over time, and these galaxies have had avery long time to get to this point.S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e 37

ResourcesPr i n t e d m at e r i a l sStarDate magazine1-800-STARDATEstardate.org/magazineStarDate: The Solar System1-800-STARDATEstardate.org/resources/ssguideStarDate: Beyond the Solar System1-800-STARDATEstardate.org/resources/btssThe Universe at Your FingertipsAstronomical Society of the Pacific, 1995ISBN 1-886733-00-7www.astrosociety.orgEl Universo a Sus PiesAstronomical Society of the Pacific, 2002ISBN 1-58381-199-0www.astrosociety.orgObserver’s Handbook(for advanced stargazers)Royal Astronomical Society of Canadawww.rasc.caPrinceton Field Guides: Stars &Planets, 4th ed.by Ian Ridpath and Wil Tirion, 2007ISBN 978-0-691-13556-4The Young Oxford Book of Astronomyby Simon and Jacqueline Mitton, 1995ISBN 0-19-521169-3Unfolding our Universeby Iain Nicolson, 1999ISBN 0521-59270-4National Science EducationStandardsNational Research Council, 1996ISBN 0309053269www.nap.edu/html/nses/htmlThe Stars: A New Way to See Themby H. A. Rey, 1976ISBN 0395245087Nearest Star: The Surprising Scienceof our Sunby Leon Golub and Jay M. Pasachoff, 2001ISBN 0-674-00467-1Cambridge Encyclopedia of the Sunby Kenneth R. Lang, 2001ISBN 0-521-78093-4Galaxies in Turmoilby Chris Kitchin, 2007ISBN 1-84628-670-0Lawrence Hall of Science:Great Explorations in Mathand Sciencewww.lawrencehallofscience.org/gemsAu d i oStarDate radio1-800-STARDATEstardate.org/radioUniverso radio1-800-STARDATEradiouniverso.org/radio/In t e r n e tStarDate Onlinestardate.orgUniverso Onlineradiouniverso.orgMcDonald Observatory Visitors Centermcdonaldobservatory.orgNational Science Teachers Associationwww.nsta.orgNASAwww.nasa.govPowers of Tenpowersof10.comNASA resources for saleeducation.nasa.gov/edprograms/core/home/NASA Education Resourceseducation.nasa.govAAS Education Resourceswww.aas.org/education/EducatorResources.phpASP Education Resourceswww.astrosociety.org/education.htmlSpanish Language Astronomy Materials Centerwww.astronomyinspanish.orgGalaxies and Cosmos Explorerwww.as.utexas.edu/gcetThe Solar System: A Firefly Guideby Giovanni Caprara, 2003ISBN 10: 155297679338 S t a r D a t e /Un i v e r s o Te a c h e r Gu i d e

More Resourcesfrom McDonald ObservatoryMcDonald ObservatoryGuidebookOur 36-page guidebook covers allaspects of McDonald Observatory,from the telescopes to the community,from history to today’s research projects.Makes a great keepsake.SKU 50401 $5.95McDonald Observatory DVDThis DVD contains two programs. In“Understanding the Universe,” tourMcDonald Observatory (14 minutes).In “Telling Secrets,” learn about theHobby-Eberly Telescope (8 minutes).SKU 50209 $10.95Subscribe to StarDateEach issue of our bimonthly magazine includes feature articles,astronomy news, skywatching information, and beautifulastrophotography. Articles are written in non-technical languageso they make good classroom resources, and the starcharts and sky calendars will help students navigate aroundthe night sky.CALL 1-800-STARDATE(8-5, Monday-Friday Central Time)Subscribe to StarDate Today!Send order to: McDonald ObservatoryUniversity of Texas at Austin1 University Station, A2100Austin, TX 78712Please make checks payable to the University of Texas at AustinNameAddressCity State ZipPhone ( ) - AMEX VISA MC DISCCard No.Cardholder SignatureExp. dateOrder Online at stardate.org/giftshopMerchandise orders (432) 426-3640Magazine subscriptions (800) 782-7328Fax orders & subscriptions (512) 471-5060Subscribe to StarDate(U.S. subscribers)•1 year $24 •2 years $42 •3 years $60QUANTITY SKU DESCRIPTION UNIT PRICECHECK ONE1yr 2yr 3yrSUBTOTALShipping & handling from chart belowTX residents, add 8.25% sales taxCurrent Sky Almanac @ $5 ea.TOTALPurchase Under $20.01 $50.01 $75.01 $100.01 Overto to to toTOTALTotal $20.00 $50.00 $75.00 $100.00 $200.00 $200.00Tax and Shipping charged on allShipping $8.00 $9.00 $10.00 $12.00 $14.00 $16.00 but StarDate subscription.UPS 2 day air add $15.00 to above rates • Canada/Mexico/Hawaii and foreign countries - triple charges

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