teacher guide - stardate.org · the stardate/universo teacher guide is published by the mcdonald...

TEACHER GUIDE

Get Close to McDonald Observatory

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432-426-3640 mcdonaldobservatory.org/teachers

Live and in PersonMcDonald Observatory offers a unique set-ting for teacher workshops: the Observatory and Visitors Center in the Davis Mountains of West Texas. The workshops offer inquiry-based activities aligned with national and Texas science and math standards. Teachers can practice their new astronomy skills under the dark West Texas skies, and partner with trained and nationally recognized astronomy educators.

mcdonaldobservatory.org/teachers/profdev

Live for StudentsThe Frank N. Bash Visitors Center features a full classroom, 90-seat theater, astronomy park with telescopes, and an exhibit hall for groups of 12 to 100 students. These programs offer hands-on, inquiry-based ac-tivities in an engaging environment, provid-ing an informal extension to classroom and science instruction. Reservations are recom-mended at least six weeks in advance.

mcdonaldobservatory.org/teachers/visit

Live on VideoVisit McDonald Observatory from the class-room through an interactive videoconference program, “Live! From McDonald Observato-ry.” The live 50-minute program is designed for Texas classrooms, with versions for grades 3-5, 6-8, and 9-12. Each program is aligned with Texas education standards.

mcdonaldobservatory.org/lfmo

Table of Contents

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To the Teacher 4Resources 38

S ta r D at e / U n i v e r S o t e a c h e r G U i D e 3

The StarDate/Universo Teacher Guide is published by the mcDonald observatory 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 change of address to starDate, the University of texas at austin, 1 University station, a2100, austin, tX 78712. Periodicals Postage Paid at austin, tX. starDate and Universo are trademarks of the University of texas mcDonald observatory.

Visit StarDate Online at stardate.org and Universo Online at radiouniverso.org

Staff eXeCUtiVe eDitor Damond Benningfield eDitor rebecca Johnson art DireCtor tim Jones CUrriCUlUm sPeCialists Dr. mary kay Hemenway kyle fricke Brad armosky CirCUlation manager Paul Previte DireCtor, PUBliC information sandra Preston

Special thanks to all the teachers who evaluated this guide.

Front CoverA Hubble Space Tele-scope view of a swath of the Coma Cluster, a collection of thousands of galaxies. Astrono-mers are studying Coma to learn about the evolution of galax-ies in clusters.

Back CoverWith Earth looming in the background, astro-nauts service Hubble Space Telescope in the cargo bay of space shuttle Discovery.

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5th Edition

TEACHER GUIDE

Support for Program num-ber HST-EO-10861.35-A was

provided by NASA through a grant from the Space Telescope

Science Institute, which is oper-ated by the Association of Univer-

sities for Research in Astronomy, Incorpo-rated, under NASA contract NAS5-26555.

Classroom ActivitiesShadow Play 6

Modeling the Night Sky 8Observing the Moon 11

Planet Tours 14Solar System Science 15Rock Cycle 16Equatorial Sundial 18Scale Models 20

Sunspots 22Spectroscope 24Stars and Galaxies 28Coma Cluster of Galaxies 30

4 S ta r D at e / U n i v e r S o t e a c h e r G U i D e

To the Teacherof the radio program content while providing some idea of how these and similar programs may be incor-porated into lesson plans.

StarDate and Universo provide additional resources through World Wide Web sites in both English and Spanish. These sites provide extensive information on the solar system, stars, galaxies, and other sci-ence topics, as well as daily, weekly, and monthly skywatching tips. Web addresses for these and other sites are provided at the back of this publication.

We occasionally produce printed guides, posters, or other resources as well. These resourc-es are distributed to the teachers who receive the audio CDs.

StarDate/Universo and Your Classroom

Each CD contains a full month of either StarDate or Universo programming. You can integrate the information from the programs into daily learn-ing experiences in your classroom in a variety of ways. You are free to copy the CDs for educational uses. Copies

may be distributed to other teach-ers, placed in your school’s library, or

used for other educational purposes. However,

the copies may not be sold or otherwise distributed for non-educational uses.

Listening SkillsStarDate and Univer-

so provide an opportunity for students to improve their listening skills. Teachers who

preview the daily program may ask questions

about the program to help students focus on the topic. Written scripts are available on-line each day

through the Star-Date Online and Uni-

verso Online web sites. Some teachers broadcast the

program over the school inter-com each day.

Note-Taking and DiscussionTo go beyond passive listening,

have your students take notes. Some teachers have found that students are more prepared to discuss the topic if they listen, take notes, then listen a second time to check their notes.

Extending Class LessonsWith their emphasis on objects in

the sky, StarDate and Universo are great sources for homework assign-ments. For this reason, some teachers play StarDate or Universo at the end of class as they make an assignment.

• Students can keep observing logs to record their observations throughout the year. Their StarDate or Universo notes prepare them to go outside and sketch what they see.

• Create a resource station where students file information they have gathered from the programs. Stu-dents may file their own drawings, data, and papers as well. Keeping your copies of the CDs and a CD player with earphones will allow stu-dents to listen individually to selected programs. Students may create a

StarDate and Universo are daily radio programs that transport listeners into the universe.

Many of the programs point out interesting events or objects in the night sky, with details on the underlying science. Other programs cover the history of astronomy and space exploration, upcoming mis-sions, recent discoveries, and relat-ed topics.

Radio stations receive the programs on monthly compact disks, and these same monthly CDs are made avail-able to teachers around the country. Hundreds of teachers incorporate the programs into their classroom instruction.

The StarDate/Universo Teacher Guide can help you integrate Star-Date and Universo programs into your daily classes. We have provided simple activities for several grade lev-els, most of which require no elabo-rate equipment. These activities are examples upon which to build similar lessons based on current StarDate and Universo episodes. You can inte-grate and apply new skills from other subject areas as you broaden stu-dents’ awareness of astronomy.

A transcript of a related StarDate radio program accompanies most activities. The scripts are boxed and denoted by a small radio transmitter logo. The scripts show the breadth

NatioNal scieNce educatioN staNdards

Each activity in the StarDate/Universo Teacher Guide meets the National Science Education Standards (NSES), which were developed with these guiding 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 the NSES “Physical Science” and “Earth and Space Science” standards. The “Science as Inquiry” standards manifest in the structure and format of the activities. Some activities overlap grade levels; many teachers will find ways to modify the activities to fit the level of their students.


database of the information filed at the resource station. Some teachers use this station as a reference source for assignments.

Bilingual InstructionUniverso can help you meet the

needs of Spanish-speaking students or students who are learning Span-ish.

• Have Universo CDs available at a listening station. Use the programs to introduce the lessons and vocabulary to bilingual students before the les-son in English.

• Have students who need support in Spanish listen to the programs to review concepts taught in English.

• Encourage Spanish students to listen to Universo programs. The written text (in Spanish) may be printed for them to follow. For some programs, students can check their comprehen-sion by listening to or reading the English version of the program after they hear the Universo program.

Cross-Curriculum ConnectionsYou can incorporate

StarDate and Univer-so into many subject areas, including:

Language Arts and Social Studies• Use the programs

on skylore to create interest in mythology and ancient civiliza-tions.• Have students keep a StarDate or Universo journal with their summaries of the programs and answers to the pre-listening questions. Journal entries may consist of phrases, sentences, paragraphs, or drawings to illustrate the core concept.• Encourage students to think on a large scale. For example, in teach-ing a unit on Thoreau, ask them to consider the vastness of the universe, using the radio shows to spark abstract thought and prepare them for existential literature.• Use the scripts from the StarDate or Universo web sites and material from Star-Date magazine as supple-mental reading materials.• Encourage students to explore the historical context and relevance of

the events and lives of the astronomers described in StarDate and Universo pro-grams.• Use the programs to explore the cultural perspectives relating to astronomy and to teach about the impact

of celestial events on cul-tural develop-ment.

Mathematics• Students can use graphs and charts during the skywatch-ing activities in this guide. They can apply concepts of proportion and percentage as

they compare the sizes of planets or the distances between planets within

our solar sys-tem. They can estimate times and relative dis-tances.• Older students can apply princi-ples of geometry and trigonometry as they explore the angles and orientations of planets and satel-lites or the position

of the Sun or Moon in the sky throughout the day or year.

Fine Arts• Encourage students to make drawings of their concepts related to the programs. For example, if the pro-gram is about sunsets,

they can draw their ideal sunset, which might lead into a dis-cussion of the Sun’s color and why it appears redder at sunrise and sunset. Or, for a program about space flight, students might draw a spacecraft vis-iting another planet or a comet.• Astronomy-related music has been popular for centuries. Your students may be more familiar with John Wil-liams’ score for “Star Wars” than Holst’s “The Planets,” but both pieces can be used as a trigger for combin-ing their ideas about astronomy with music.

Individualized LearningBecause StarDate and Universo top-

ics range from basic to more complex concepts, you can use them with stu-dents of all ages and ability levels.

• With a copy of the program’s script, students can highlight key concepts and challenging words as they listen to the program.

• Have students visit StarDate Online or Universo Online as an enrichment activity. They can search the web site for answers to their astronomy ques-tions or read the daily Frequently Asked Question.


Everyone and everything has a shadow. Shadows illustrate how three-dimensional objects can be viewed in two dimensions. Younger students can learn about the Sun’s relative motion in the sky as they experiment 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 Sun at noon?” Depending on the age of the child, responses might be “straight up,” “in the sky,” “overhead,” or “in the south.” Ask, “What is a shadow?” 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 still while the other team members trace the outlines of both the statue’s feet and shadow on the pavement. When all the tracings are completed, the entire 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) and hold the same position again.

aNalYsisWhat has changed?

aNswerStudents should notice that the length and position of the shad-ow have changed. Younger chil-dren may think that the “statue” changed position. Ask them to predict where the shadow will be in three hours. Repeat the tracings about once per hour until the end of the school day. The shadows will grow progres-sively shorter in the morning until mid-day, after which they will grow longer. It is best to do the tracings throughout the school day. Note that the shadow never shortens enough to disappear, which means that the Sun doesn’t pass directly overhead at noon (unless you live between the tropics). Depending on the grade, students may

Shadow PlaySunwatcherSUntil well into the last century, one of

the most important people in the pueblos of the southwest was the Sunwatcher. Each day, he watched the Sun rise, using

hills or other objects to track its motion along the horizon. His observations told the tribe when to plant or harvest crops, and when to conduct important ceremonies.

The Sunwatchers may have been carrying on a tradition established by some of the ancestors of the pueblo people — the Anasazi, a Navajo name that means “the ancient ones.” They built a large, well-ordered civi-lization in the Four Corners region a millennium ago.

Archaeological sites at several Ana-sazi villages suggest that they watched the Sun carefully. One example is the Sun room in Hovenweep Castle, a ruin in southeastern Utah. Doorways and windows in the room align with the sun-set on the summer and winter solstices — when the Sun appears farthest north and south in the sky — and the equi-noxes, when it’s half-way between.

Nearby, a pair of buildings atop Cajon Mesa apparently served as a solar calendar. Sunwatchers kept track of the Sun’s motion from a series of windows. They also used the shadows of the two buildings to determine the arrival of the solstices and equinoxes.

The most famous Anasazi sunwatch-ing sites are in Chaco Canyon, in northwestern New Mexico. In fact, quite a few people are visiting the can-yon this week to watch the sunrise on the summer solstice.

This is the transcript of a StarDate radio episode that aired June 19, 2001. Script by Damond Benningfield, ©2001.


measure the lengths of the shadows or even graph the length versus time of day. Discuss the results.

actiVitY twoThis activity demonstrates the daily motion of Earth. We perceive the Sun as rising, crossing the daytime sky, and setting. It is actually Earth that moves.

PreParatioNInside the classroom, arrange all the children in a circle around a lamp, which represents the Sun. The teacher should demonstrate and then ask the children to “spin.” (Young children prefer the term “spin” to “rotate” when thinking about Earth’s motion.)

deMoNstratioNTo find the proper direction, place your right hand over your heart (the position for reciting the Pledge of Allegiance) and rotate in the direction the fingers point. (As an extension, walk around the lamp to model Earth’s annual motion around the Sun. Don’t try to spin and walk at the same time; it takes 365.25 spins to make a year!)

aNalYsisWhat has changed?

aNswerWhen children are facing the lamp, it is day. When they are facing away from the lamp, it is night.

actiVitY tHreePreParatioNInside the classroom, demonstrate the connection between the first two activities. First, tape the action figure onto the globe at your geographic location. Still using the lamp to represent the Sun, place the globe at least 6 feet away from the lamp (ideally with the globe’s spin axis tilted rela-tive to the lamp to represent the current season, so it will be tilted away from the lamp in the winter and toward it in the summer).

exPeriMeNtDarken the room and spin the globe so that everyone can see a change in the length and position of the figure’s shadow.

aNalYsisHow does the figure’s shadow compare to the childrens’ shadows outside?

aNswerThe behavior of the shadows should be similar. Spinning the globe counter-clockwise when looking down on the north pole will show the proper move-ment of 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 day and night.


•ContentStandardinK-4EarthScience (Objects in the sky, ChangesinEarthandsky)

•ContentStandardinK-4Scienceas Inquiry (Abilities necessary to doscientificinquiry)

Light bulb


This activity extends “Shadow Play” (page 6) to include more solar system objects and to examine their motions.

PreParatioNEach individual or group needs one copy of the constellation strip on page 9. The teacher needs individual constellation pictures and cards with the names or pictures of the following objects: Sun, Earth, Mercury, Mars, and Jupiter. Allow each group of 2-3 students to glue or tape the strips togeth-er, 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 the pictures. 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 represent the position of the Sun in relation to the constellations. Then ask them to place the other ball where they think Earth should be in relation to the Sun and the constellations and to explain to their partners why they chose that position. Ask the students to identify which side of Earth will be day and which side will be night. When the Sun is “in” a certain constella-tion (that is, standing on Earth, if you had the ability to see stars in the daytime, which constellation would be behind the Sun), what constella-tion is seen at midnight? Your interactions will depend upon the student responses. If they place Earth rather than the Sun in the center, ask them to explain. For now, accept all answers.

Ancient peoples tracked which constellations appeared in the direction of the Sun. They usually watched the sky near sunrise. For this model, the Sun is in the middle and Earth goes around it (counterclockwise as seen from the north pole). The stars are very distant compared to the Earth-Sun distance.

ACTiviTy 2Cut each figure out of one strip and paste it on an individual card. Pass the cards out to 13 students, who stand in a circle facing inward. (For a small group, post the cards on backs of chairs to make a circle.) Make sure they

follow the same order as the loop. Choose one student to be the Sun and stand in the middle of the circle. Allow anoth-

er student to individually model Earth’s motion throughout the year, recalling that the direc-

tion of rotation and revolution are the same. For Earth, one turn around the Sun takes one year. (Although rotation can be considered

simultaneously, remember that Earth rotates in 24 hours, and anyone who spins 365 times

as they “orbit” the Sun will become dizzy!) As an extension, you may wish to include Earth’s tilt. Choose a

spot 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 10


•ContentStandardinK-4EarthandSpaceScience(ChangesinEarthandsky,Objectsinthesky)

•ContentStandardin5-8Earthand Space Sciences (Earth in the solarsystem)

•ContentStandardinK-4PhysicalScience (Position and motion of objects)

Modeling the Night Sky

Although Ophiuchus (oh-fee-YOO'-kus) is not a traditional constellation of the zodiac, the Sun passes through its borders in December. In one year, the Sun passes through 13 constellations. In classical mythology, Ophi-uchus was known as the serpent bearer.

PISCES AQUARIUS CAPRICORNUS

D C


C B

VIRgO LEO CANCER

B A

gEmINI TAURUS ARIES

A D

SAgITTARIUS OPHIUCHUS LIBRASCORPIUS


OphiuchuS and SerpenS Two constellations that don’t get a lot of respect are in the southwest this evening, above the Moon and the bright planet

Jupiter. One of them is slighted by any-one who can name the 12 signs of the zodiac. The other was slighted by the people who established the constella-tion boundaries: they chopped out its middle.

The constellations are Ophiuchus, the serpent bearer, and Serpens, the serpent.

Ophiuchus is one of the largest con-stellations. More important, it lies along the ecliptic — the Sun’s path across the sky. The constellations along this path form the zodiac. But Ophiuchus isn’t included in the lineup, even though the Sun spends more time inside its borders than in Scorpius, which is next door.

Ophiuchus represents the founder of medicine. In myth, he was such a good healer that he even brought the dead back to life. That was reminiscent of the powers of a snake: It can kill, but it also rejuvenates itself every year when it sheds its skin. So in the sky, the physician is also known as the serpent bearer.

Appropriately enough, he’s holding on to Serpens. The serpent’s head is to the west of Ophiuchus, with the tail to the east — severed by the body of Ophiuchus.

Serpens and Ophiuchus are well up in the southwest at nightfall. Look for the crescent Moon quite low in the sky, with brilliant Jupiter and the bright orange star Antares to its upper left. Ophiuchus and Serpens stretch out above this bright trio.

We see different stars at different times of year because Earth orbits (revolves around) the Sun. Some constellations are small, while others are large. The Sun appears to move from one constellation to another in as few as 6 days or as many as 43.

Add more celestial objects to your model by handing planet cards to more students. These objects orbit the Sun like Earth, but at different rates. This works best if they come in one at a time, each with their own rate of orbit-ing the Sun. The following table recommends some approximations to use, along with the exact values, for periods of revolution (the time it takes for the object to revolve around the Sun one time). Distance scales are not preserved in this activity. For example, tell the students that Mercury orbits the Sun four times in one Earth year. So the person who represents Mercury has to race around the Sun four times while Earth goes around only once. Some students will count this out. For younger students, draw-ing the circles on the floor helps them maintain the proper distances. Stop occasionally to ask, “If you are on Earth, where or when can you see that object?” Add more or fewer objects depending upon the age of the group. For older students, model sunrise/sunset and ask what objects are vis-ible in the sky at various times of day (just after sunset or at midnight, for example) and in which constellations they appear. If you have already studied phases of the Moon (see “Observing the Moon,” page 11), it can be inserted into this model, orbiting Earth in about one month while Earth orbits the Sun in one year.

Object Approximate period Actual period

Mercury 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 years

eValuate

The asteroid Ceres has a period of 4.6 years. Where would it go in this • scheme? (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 would be difficult to model and adding Venus would make it crowded. The other planets orbit so slowly that they would barely move!)

Place a plain piece of paper under the loop and sketch the number of • orbits (or partial orbits) for Earth and two other objects.

Teaching note: Although this activity does not indicate relative distanc-es, it is correct that all of the planets orbit the Sun in approximately the same plane. That is why we can limit ourselves to just the constellations that form one great circle on the celestial sphere.

This is the transcript of a StarDate radio episode that aired September 17, 2007. Script by Damond Benningfield, ©2007.


Does the Moon always look the same? Does its surface look differ-ent at different times? What will your students say when you ask them these questions?

Many students are aware that the Moon goes through phases, but except for the “man in the Moon” — which many admit they have a hard time seeing — they probably haven’t thought about the surface of the Moon and how we view it from Earth. Some students may men-tion that the Moon changes colors. It actually doesn’t — the Moon’s color changes due to the effects of our own atmosphere, not anything intrinsic to the Moon.

MaterialsClear skies•

Notebook•

Soft drawing pencil•

Binoculars•

Chart on page 13•

PreParatioNFirst, figure out when you can see the Moon. Use the StarDate Sky Alma-nac or a calendar to find the Moon’s phase on the day you will carry out this 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 activ-• ity, it really isn’t. “New Moon” means “no Moon.” During this phase, the Moon is in the sky all day, but it lies in the direction of the Sun and its night side is facing Earth. That means no lunar surface features will be visible.

During full Moon, patterns of dark and light on its surface are easy to • distinguish. That’s when the “maria” — smooth, almost crater-free regions on the Moon — are easiest to see.

During crescent or quarter phases, the craters and mountains cast dis-• tinct shadows and become more noticeable.

Once you know the Moon’s phase, the chart provided here will help you decide the best time of day (or night!) for lunar viewing.

actiVitYDraw two 10-cm circles in your observing notebook. List the time, date, sky conditions, and location. Indicate the phase of the Moon within your circle. Now, sketch in the light and dark areas. A soft pencil works best. Some students like to smudge their lines to show light and dark. If you have binoculars, repeat the activity using them. Binoculars will allow you to see a lot more detail. At another phase (at least five days later), repeat the activity.


•ContentStandardinK-4EarthandSpaceScience(ChangesinEarthandsky,Objectsinthesky)

•ContentStandardin5-8EarthandSpace Sciences (Earth in the solar system)

•ContentStandardin5-8Scienceas Inquiry (Abilities necessary to doscientificinquiry)

Observing the Moon

Lunar eclipse

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Phase New First Quarter Full Last Quarter

Rise Sunrise Noon Sunset Midnight

Highest in Sky Noon Sunset Midnight Sunrise

Set Sunset Midnight Sunrise Noon

aNalYsisCompare the naked-eye and binocular drawings done on the same date with each other. What details are visible? Can you identify any features from the lunar map? Now compare the drawings from one date to the other.

exteNsioNFor an in-class activity, make craters by dropping marbles or pebbles into a deep basin of flour sprinkled with dry chocolate milk mix. You should get nice craters with elevated edges, and some with a series of splashed out materials centered on the crater. In a darkened room, shine a flashlight onto the cratered surface and show how the angle of the flashlight deter-mines the length of the shadows. Students can research the surface of the Moon in the library or on the Internet.

As a math extension, calculate the angle between the Sun and Moon for different phases.

For English, write a poem about the Moon.

Full earth The Moon is AWOL right now. It pass-

es between Earth and the Sun early tomorrow, so it’s hidden in the Sun’s glare. And even if the Sun wasn’t in the way, there

wouldn’t be much to see: It’s night on the lunar hemisphere facing our way, so the entire disk is dark.

Well, almost dark. The Sun is shining on the far side of the Moon, so it’s not lighting up the side that faces Earth. But the side that does face Earth is getting some sunshine — reflected off of Earth.

We can see this “earthshine” when there’s a crescent Moon in the sky, because it makes the dark portion of the lunar disk look like a gray phantom.

Right now, the earthshine is at its most intense. That’s because there’s a full Earth in the lunar sky. Earth covers an area more than 13 times greater than the Moon does. And on average, each square mile of Earth’s surface reflects more than three times as much sunlight back into space. So a full Earth is about 40 times brighter than a full Moon.

While a full Moon always looks the same, a full Earth is constantly chang-ing. Anyone standing on the Moon would see the entire surface of Earth as our planet turns on its axis. So they’d see different continents and oceans, plus the unceasing motions of clouds in the atmosphere. And since the same side of the Moon always faces Earth, our planet would always appear in exactly the same spot in the sky — a bright blue and white ball spinning in the sunlight.


Above: Impact craters and volcanic valleys on the lunar surface.Right: An Apollo 15 astro-naut salutes the flag.

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This is the transcript of a StarDate radio episode that aired May 7, 2005. Script by Damond Benningfield, ©2005.


learNiNG tHe luNar laNdscaPe

Ocean of Storms

Seaof Rains

Sea of Tranquility

Sea of FertilitySea of

Nectar

Sea of Clouds

Sea of Moisture

Sea of Serenity

Sea of Vapors

Sea of Cold

Bay of Dew

Tycho Tycho

Copernicus

Langrenus

Taruntius

Kepler

Aristarchus

Plato

Archimedes

Ocean of Storms

Seaof Rains

Sea of Tranquility

Sea of FertilitySea of

Nectar

Sea of Clouds

Sea of Moisture

Sea of Serenity

Sea of Vapors

Sea of Cold

Bay of Dew

Copernicus

Langrenus

Taruntius

Kepler

Aristarchus

Plato

Archimedes

Sea of CrisesSea of Crises

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Planning to take a vacation soon? Visit Phobos! Small and cozy, Pho-bos orbits the fourth planet from the Sun in less than eight hours. From your observation deck on Phobos, you will have a superb view of Mars. You will see its mountains, polar ice caps, and the largest vol-cano in the solar system. Call your cosmic travel agent today!Try this creative activity to help your students explore the solar system in an imaginative manner.

PreParatioNUse StarDate or Universo CDs or printed materials such as StarDate: The Solar System or the StarDate/Universo websites to find information about solar system objects. As an aid, provide some examples of real travel bro-chures or websites with travel ads available for students to preview. For secondary classrooms, a good resource is Active Physics: Sports by Arthur Eisenkraft (ISBN 1-891629-04-02).

actiVitYBreak the class into teams that will research one planetary body (if you have a large number of teams, you can include some of the moons of the solar system, or comets and asteroids). The students use the information they collect to create travel posters, brochures, or television or radio com-mercials for their object.

Each project should include real facts about the solar system object, but may use “far-out” features to form the basis of unusual recreation oppor-tunities. When everyone is finished, each team presents its product to the rest of the class.

assessMeNtDevelop a grading rubric for dif-ferent grades, keeping in mind the standards. In addition to “facts” about solar system objects, the rubric should ascertain whether students use physical data to make compari-sons. Making comparisons is the key to learning science in this activity. Some teachers may be comfortable with allowing the students to design the rubric for their class after they have started the project; others may want to pass the rubric out at the beginning of the assignment. One teacher had students make Power-Point presentations and gave extra credit for working some mythology and images into the presentation.

Planet Tours

MOOn and Jupiter On the scale of our everyday lives,

Earth is a big place. It’s so big, in fact, that an airliner, flying nonstop, would take about two days to circle its equator. But

our planet is tiny compared to Jupiter, the giant of the solar system. It’s 11 times bigger around than Earth is, so that airliner would need about three weeks to circle Jupiter’s equator.

And the sights out the window would be spectacular.

Jupiter doesn’t have a solid surface, so you wouldn’t see any mountains, deserts, or oceans. But the Jovian atmo-sphere is filled with giant storms, and with belts of clouds that race around the planet at hundreds of miles an hour.

To avoid turbulence, you’d have to go around the biggest storm systems. That could add days to the trip, though, because the storms can be as big as Earth. And they produce lightning bolts that are hundreds of times as powerful as those on Earth. At night, such blasts might be visible for thousands of miles.

Different chemicals in the atmosphere add color to the clouds, so you’d see shades of yellow, brown, and red mixed with the white clouds that’re made of water vapor.

And if you’re afraid of heights, you wouldn’t want to look down: the cloud layers atop the Jovian atmosphere are scores of miles thick, so it would be a long way down.

Future tourists may detour around Jupiter’s Great Red Spot, a storm that is larger than Earth.

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•ContentStandardin5-8EarthandSpace Science (Earth in the solar system)

•ContentStandardin5-8PhysicalScience (Properties of objects and materials)

This is the transcript of a StarDate radio episode that aired February 19, 2006. Script by Damond Benningfield, ©2006.


In this activity, students explore and compare planets in our solar system. Each student becomes the “ambassador” for a planet and pre-pares by researching their planet, then meets with other ambassadors to 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. Stu-dents in 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 or striking about their planet — an impression.

Have one ambassador from each group join with ambassadors from other groups. Each group need not have exactly the same planet mix, but there should not be duplicates of a planet within a solar-system group. The ambassadors interview each other to exchange information and impres-sions.

Once they have shared their information, the ambassadors should consider how they could organize themselves. Some might want to arrange them-selves in order of distance from the Sun. Others might notice that some planets are small and rocky and others large and gaseous. “Solar systems” may invent several organization schemes. They will note interesting or unexpected planetary features. For instance, Olympus Mons, a “super vol-cano” 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 sys-tem. The teacher should help students sum up the results, noting similarities and differences among the schemes. Most planetary scientists organize planets into two divisions: terrestrial (like Earth) and Jovian (like Jupiter). Terrestrial planets are small and rocky with few or no moons, and they are close to the Sun. Jovian planets are gaseous giants with many moons, and are farther from the Sun.

exteNsioNWhat planet or object should NASA choose for future human exploration? Ask the “solar system” to choose a planet or moon. With pictures and text describing its features, design a spacesuit for the visit. For instance, Jupiter poses a serious challenge — it’s mostly high-pressure gas. What materials would the astronaut need to stay alive? How would the suit help the astronaut explore Jupiter? Would wings help?

Compare planets in our solar system to new extrasolar planets that astronomers have discovered.

Solar System Science

The solar system is filled with amaz-ing sights, including (from top), an avalanche beneath a Martian ice cap, the surface of Saturn’s big moon Titan, and Saturn‘s bright rings.


•ContentStandardin5-8Earthand Space Science (Earth in the solarsystem)


•ContentStandardin5-8Physi-cal Science (Properties of objects andmaterials)

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This activity combines the concept of Earth’s rock cycle with the char-acteristics of other planets in the solar system. After learning about Earth’s rock cycle and the basic characteristics of objects in the solar system, students can consider how to extend this concept to other objects. The student’s goal is to create a rock cycle for each selected solar system object.

PreParatioNFirst, as a class, students should agree on a course of action based on their own 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 their peers. This involves not just presentation, but also discussion about the supporting evidence for their rock cycle claims. As an extension, stu-dents can investigate the case for Pluto and come up with their own con-clusion — what is Pluto?

Materials

• StarDate: The Solar Sys-tem (or Universo Guía del Sistema Solar)

• Slide projector and slides (optional)

• Internet access, com-puter, and browser (optional)

ACTiviTyeNGaGe Begin by reviewing the basics of Earth’s rock cycle. Then pose a question about other members of our solar system (not just planets): do they have rock cycles, too? Record students’ driving questions and discuss ways to go about answering those questions. You may wish to reserve Pluto as a spe-cial solar system member for later investigation (see the Extend section).

exPloreDivide students into small groups of four to six. Each group should inves-tigate a different planet, depending on the result of the class brainstorm. StarDate: The Solar System will help students gather information about planetary features that provide clues to the planet’s rock cycle. If students have trouble, help them consider Earth’s rock cycle and how it relates to

Rock Cycleplanetary therMOStat Even on a winter day, our Earth is a

fairly warm, comfortable home for life. That’s thanks in part to the carbon dioxide in our air. Although it accounts for only

a tiny fraction of the atmosphere, it warms our planet by about 50 degrees Fahrenheit, and keeps Earth from turn-ing into a ball of ice.

Carbon dioxide is called a green-house gas. Like the glass in a green-house, it traps heat, in the form of infrared energy. So sunlight can come in, but much of the heat can’t get out.

In the distant past, the atmosphere contained much more carbon dioxide. But rain washed most of it out of the air. It combined with other chemicals to form carbonate rocks, such as limestone. Today, some carbon dioxide is pumped back into the air by volcanoes.

There’s also carbon dioxide in the atmospheres of our two closest plan-etary neighbors, Venus and Mars.

Mars may have undergone the same process as Earth, with almost all of its carbon dioxide now locked up in rocks. The Martian atmosphere is thin, so Mars is cold and desolate, and temperatures normally stay well below zero.

On Venus, though, the carbon diox-ide remained in the atmosphere. Today, Venus’s atmosphere is 90 times thicker than Earth’s, and it’s made almost entirely of carbon dioxide, so the sur-face temperature is about 860 degrees Fahrenheit.

Only on Earth is the balance just right to provide a comfortable home for life.

Earth’s Rock Cycle

SEDIMENTARY

METAMORPHIC IGNEOUS

exposure & erosion

melting

melting

heat & pressure

cooling &chemical change

exposure & erosion

tim

Jon

es

This is the transcript of a StarDate radio episode that aired February 22, 2000. Script by Damond Benningfield, ©1999.


Earth’s features. Air and water erode rocks into sediments. Earth’s mantle heats buried rocks to make metamorphic rocks. Continents collide and raise mountains for water and air to erode.

exPlaiNThe planets closest to the Sun (Mercury, Venus, Earth, and Mars) are rocky; they will most likely show evidence of a rock cycle. The gas giants (Jupiter, Saturn, Uranus, and Neptune) won’t. But these gas giants have rocky moons that can be investigated. For each solar system object, infor-mation about its surface features, agents of erosion, and geologic structure under the crust will provide the major clues necessary to construct a possi-ble rock cycle. Check your school’s library for available resources. A wealth of information about the planets resides on StarDate Online. One effective way to organize the research is to break the class into research groups, with each focusing on one planet or moon.

exteNdBreak the students into another set of groups with each member being an expert on a different planet. These groups discuss some of the following questions:

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 your • object, such as adding liquid water to Mars or changing Earth’s atmo-sphere. Would these changes affect the rock cycles on these bodies?

eValuateAfter their investigation, each group presents its object’s rock cycle to the class. During their presentation, students should point to particu-lar features of their planet as evidence that supports different phases of their hypothetical rock cycle. This could be a presentation involving posters or computer graphics. Or it could be something else a bit more interactive, such as a poem or song.

Rain, wind, rivers, and ocean tides erode surface rocks, washing mate-rial into the oceans to begin the rock cycle anew (below). Volcanoes on Io (lower left), Earth (bottom), and other bodies deposit new rocks on the surface.


•ContentStandardin5-8Scienceas Inquiry (Abilities necessary to do scientific inquiry, Understand-ingaboutscientificinquiry)

•ContentStandardin5-8EarthandSpace Science (Earth in the solar system, Structure of Earth system)

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egyptian StOnehenge Summer arrives in the northern hemi-

sphere today, as the Sun appears farthest north for the entire year.

In centuries long past, skywatch-ers around the world watched for the solstice at special observatories — circles of stones. The most famous is Stonehenge in England, but circles of much smaller stones were found in the Americas, too.

The oldest of these stone observatories may have been built in southern Egypt, at a site called Nabta. It was used 6,000 years ago, and perhaps even ear-lier — at least a thousand years before Stonehenge.

Anthropologist Fred Wendorf of South-ern Methodist University discovered the site in 1973. Last year, studies by Wen-dorf and Colorado astronomer J. McKim Malville confirmed that Nabta had an astronomical function.

Among other artifacts, the site contains a 12-foot-wide “calendar circle” of small stones. Two pairs of stones stand across the circle from each other. If you look through the spaces between each pair, you’ll see the point where the Sun rose on the summer solstice thousands of years ago. This alignment was important to the people who lived at Nabta because mon-soons brought a few inches of rain to the region soon after the solstice.

Over the centuries, though, the rains dried up and Nabta was abandoned. But the people of Nabta may have left a legacy. Their culture may have stimulated the formation of Egypt’s Old Kingdom — the civilization that built the great pyramids.


One of astronomy’s first tools to measure the flow of time, a sundial is simply 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 many types of sundials; an equatorial sundial is easy to make and teaches fun-damental astronomical concepts. The face of the sundial represents the plane of Earth’s equator, and the stick represents Earth’s spin axis.

PreParatioNFirst, find your latitude and longitude and an outdoor observing site in a clear (no shadows) area. Determine north (from a map, or by finding the North Star at night and marking its location). Assemble the equipment as described below. Use a flashlight to demonstrate how to position and read the 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 tem-plate, making sure the dial faces are lined up. Cut a cross in the center hole where the straw will be snuggly inserted. Mark the straw using the latitude strip as a guide. First mark the bottom of the straw at one end, then mark a line corresponding to your latitude. Place the straw in the template hole at the line marking your latitude. The south face of the template should aim toward the bottom of the straw. Make sure the stick and template are perpendicular. 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 surface with the bottom of the straw and the folded edge of the template both resting on the ground. Aim the straw with the top pointing due north. (If done correctly, the straw will point at the celestial north pole, where we see the North Star at night.) Record the time on the sundial at least four times in one day, with measurements at least an hour apart. Each time, also record the “clock” time for your date and location. Try this experi-ment during 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 longitude difference from the center of the time zone), there is a correction of four min-utes. Also, the Sun’s location in the sky changes with the seasons, and a correc-tion of up to about 15 minutes for the “equation of time” must be made. Read the correction from the graph on page 19. Daylight Saving Time changes results by one hour.

2. The shadow of the straw is cast on the north face from March 21 to Septem-ber 21, and the south face from September 21 to March 21. The plane of the template is aligned with the celestial equator. The Sun is north of the celestial equator during the first period (spring and summer) and south of the celestial equator during the second (fall and winter).

Equatorial SundialNatioNal scieNce educatioN staNdards

•ContentStandardin5-8EarthandSpace Science (Earth in the solar system)


This is the transcript of a StarDate radio episode that aired June 22, 2003. Script by Damond Benningfield, ©1998, 2003.

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Correction for the “Equation of Time”

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latitude striP


Without being informed of the expected product, the students will make a Play-doh model of the Earth-Moon system, scaled to size and distance. The facilitator will reveal the true identity of the system at the conclusion of the activity. During the construction phase, students try to guess what members of the solar system their model represents. Each group receives different amounts of Play-doh, with each group assigned a color (red, blue, yellow, white). At the end, groups set up their models and inspect the models of other groups. They report pat-terns of 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 the • same color.

Large paper sheet as a work surface for rolling and shaping the Play-doh•

PreParatioNColor code each amount of Play-doh: red, 2 cans; blue, 1.5 cans; yellow, 1 can; 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. Distribute Play-doh and one large piece of paper to each group.

actiVitYIntroduce the problem Tell the groups that they will make a scale model of two members of our solar system. Do not reveal that it is the Earth and Moon — that’s the sur-prise that makes this activity memorable. Along the way, they can make guesses about what the model represents.

Divide the Play-doh Tell groups to divide their Play-doh into five equal pieces. They may use whatever creative and clever means they can think of to solve this problem. Example solution: Roll the Play-doh into a long cyl-inder, then divide it into pieces. A 50-cm cylinder can be cut into 10-cm lengths, then formed into spheres. Tell groups to divide up one of the larg-er pieces 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 piece previously set aside) into one big sphere. Roll the remaining small piece into a little sphere.

Scale ModelsSOlar eclipSeThe Moon will cover up the Sun early

tomorrow, briefly turning day to night. Unfortunately, though, it’ll happen while it’s already night here in the United States, so

we’ll miss out on the show.The event is a total solar eclipse. It

happens thanks to a coincidence in the way the solar system is laid out: Even though the Sun is about 400 times wider than the Moon, it’s also about 400 times farther away. So when the geometry is just right, the Moon can just cover the solar disk.

As the Sun disappears, the air gets cooler, and the sky turns dark. The Sun’s hot but thin outer atmosphere, the corona, forms delicate streamers of light around the Moon. And the first or last moment of sunlight can form a “diamond ring” — a thin ring of light around the Moon, with a bright burst where sunlight streams through canyons or between mountains.

The Moon’s orbit is tilted a little, so most months the Moon passes just above or below the Sun, and there’s no eclipse. But two or more times a year, the Moon’s orbit lines up just right, creating an eclipse. Many eclipses are partial, so the Moon appears to only nick the Sun. But this month it goes right across the heart of the Sun, creating a beautiful eclipse.

The total eclipse is visible along a thin path that runs through China and Russia, across the tip of northern Green-land, and just into Canada. The partial eclipse is visible across a much wider area, but it doesn’t include the U.S.

This is the transcript of a StarDate radio episode that aired July 31, 2008. Script by Damond Benningfield, Copyright 2008.


Make a guessAfter they have made two Play-doh spheres, ask each group to write down three guesses about what these solar system objects might represent. Dis-cuss the guesses with the students. At least one student will guess they are Earth and the Moon. Next, ask them to make a guess of how far apart to put their Earth and Moon spheres to make a true model. A scientist follows up and tests guesses with observations and measurements.

Measure the big sphere diameter; this is the diameter of EarthTell each group to measure the diameter of the Earth sphere. They may cut the sphere in half. They may measure with a string and mark off the diameter or use a meter stick.

Separate the big and little spheresAfter students have measured the Earth and Moon sphere diameters, ask each group to place the big and little spheres apart by 30 Earth-sphere diameters. Groups with the least Play-doh will probably be able to lay out their models on the table top. The two-can group might have to lay out its model on the floor.

Inspect other models, compare, and analyzeAfter all the groups have laid out their models, ask everyone to inspect other groups’ models. Discuss the results. Models will differ in three main ways, besides the color of the Play-doh: the relative sizes of the Earth spheres, the relative sizes of the Moon spheres, and the distance between the spheres. But all of these differences are related to the same set of pro-portions. The ratios of Earth diameter:Moon diameter and Earth diameter:separation distance are the same for each model.

exteNdThe Sun is about 150 million km from Earth. Estimate how many Earth diameters and Earth-Moon distances in your system would be needed to put the Sun in your model. Compare the sizes of the Sun and the Moon’s orbit around Earth.

BacKGrouNd

Earth to Moon RatioEarth Moon Ratio

Diameter (km) 12,756 3,475 3.7

Volume (m3)V= 4/

3r3

1.08 x 1021 2.2 x 1019 49

Since spherical volume is 4/3 r3, the ratio of Earth-to-Moon volume is 49.5. The mean separation between Earth and the Moon is 384,500 km. So the ratio of the Earth-Moon separation to Earth’s diameter is:

In round numbers, Earth’s volume is 50 times that of the Moon, and the Moon is about 30 Earth diameters away. The Sun is 11,759 Earth diameters, or 390 Earth-Moon distances away from Earth. The diameter of the Moon’s orbit is twice the Earth-Moon distance (384,500 km x 2 = 769,000 km); the diameter of the Sun is 1,392,000 km. The Moon’s orbital path around Earth is about half the diameter of the Sun.


•ContentStandardin5-8EarthScience (Earth in the solar sys-tem)

•ContentStandardin5-8Scienceand Technology (Students should develop abilities of technological design)


384,500 km12,756 km = 30 Earth diameters.


The Sun is a huge sphere of gas. The visible layer of the Sun, which we view as the surface, is the photosphere. Its temperature is about 6,200 degrees Celsius (10,340 degrees Fahrenheit). Above the surface are the chromosphere and corona. Sunspots are some of the most noticeable features of the Sun.

Materials

• Telescope (with finder covered)

• Piece of white cardboard mounted on a tripod

PreParatioNThe 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 until its shadow is smallest. If your telescope doesn’t have a special motor, the image will slowly track across the cardboard as Earth rotates. You may use binoculars, although too much sunlight can cause heat to build up inside the binoculars and dam-age them. For binoculars, the standard size (7x35) works satisfactorily.

exPeriMeNtDraw a circle around the edge of the Sun on some paper placed over the cardboard. Now quickly sketch the positions and sizes of all the vis-ible sunspots. Write the time and date on the edge of the paper. Repeat your observations over several days or weeks. (If you trace the images on very thin paper, you can later overlap them to see changes.) Be careful to include the fine detail that surrounds some sunspots. An alternative is to download images from web sites each day to use for this activity or to com-pare to your own data.

aNalYsis1. Can you identify any sunspots or sunspot groups? Did they change shape, size, or position over time?

2. If you move the cardboard screen farther away, what happens to the image?

3. (Advanced) The diameter of the Sun is about 1.4 million km (864,000 miles). Measure the diameter of your image and estimate the physical size of your largest sunspot. Earth is 12,700 km (7,900 miles). Compare your largest sunspot with the size of Earth. Find the size of the sunspot with a proportion equation:

4. Why are sunspots dark?

SunspotsreverSed pOlarityWhen a character in TV science fiction

faces a tough technical prob-lem, one solution always seems to work: reverse the polarity.

That may not fix problems in real life, but for the scientists who study the Sun, reversing the polarity is a big event. It signals that the Sun has started a new 11-year cycle of magnetic activ-ity.

A new cycle began in January, when telescopes on the ground and in orbit measured a small sunspot — a rela-tively cool, dark magnetic “storm” on the surface of the Sun. The observations showed that the polarity of the sunspot was reversed from that of the sunspot before it.

As the Sun spins on its axis, different layers of hot gas spin at different rates. That generates a powerful magnetic field around the Sun.

Over a period of several years, the lines of magnetic force get twisted and tangled. That produces many more sunspots. The lines can also cross each other, creating “short circuits” — pow-erful explosions of energy and particles. These outbursts can disrupt communica-tions and electrical systems on Earth.

At the end of a cycle, the Sun’s mag-netic field flips over: magnetic north becomes magnetic south, and vice versa.

The Sun has been quiet for the last few years. But the start of a new cycle means that it’ll get busier in the years ahead. The new cycle should peak around 2012, and end around 2019 — when scientists will once again be waiting for the Sun to reverse polarity.

1,390,473 km

diameter of Sun’s image in mm

sunspot diameter in km

sunspot image in mm=

This is the transcript of a StarDate radio episode that aired June 13, 2008. Script by Damond Benningfield, ©2008.


aNswers1. Sunspots change size and

shape over a period of days. The Sun rotates on its axis in

about 25 days (its equator rotates faster than its poles). Observations taken over a period of several days should

show this.

2. As you move the cardboard screen back, the image becomes

fainter and larger.

3. Large sunspots can equal Earth in diameter.

4. Do the following demonstration to illustrate that sunspots appear dark since they are cooler than the photosphere (they are about 4,500 degrees C/7,100 degrees F). Attach a dimmer switch or rheostat to a clear incan-descent light bulb. Place the bulb on its side on an overhead projector. With the projector on, focus the bulb so that the filament appears as a sharp silhouette on the screen. Turn up the power until the filament glows against the screen, then turn the power down until the filament is just barely dark against the background. Turn off the projector and the bulb will seem to glow dimly by itself. Sunspots are only “dark” with respect to the hotter, brighter back-ground of the photosphere.



Spanning more than 13 times the total area of Earth’s surface, this large group of sunspots photographed in 2001 coincided with the peak of the 11-year solar cycle (see sunspot number chart below). Inset: Close-up view of a typical sunspot.

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Do not look directly at the Sun, especially with a telescope. You can PERMANENTLY DAMAGE YOUR EYES! When working with students, it’s best to cover the finder telescope completely so that they cannot look through it. Never trust filters that

go into the eyepiece or that cover the objective.


Just as a geologist collects rocks or minerals and a botanist collects plants, an astronomer collects light. Astronomers usually cannot touch the objects they study, like stars or galaxies. But they can analyze the light these celestial objects radiate using a spectroscope. When an astronomer looks at a star through a spectroscope, he or she sees a colorful spectrum that is full of information.

Students will construct their own spectroscope as they explore and observe spectra of familiar light sources. Extension activities expand their understanding of different kinds of spectra and sharpen their observing skills. You may challenge more advanced students to make technological improvements to their instruments.

Materials

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. This will help fasten the card onto the spectroscope tube.

2. Fold each 3x2.5-inch card in half along the short side, then snip a slit perpendicular to the fold about half a centimeter from either corner of the fold. Punch a hole about two centimeters down in the fold. The open-ing should be about a centimeter wide.

Preparing the grating1. Sandwich the transmission

grating material between two sheets of transparency mate-rial. Try not to touch the very sensitive grating with your fingers.

2. Cut the “sandwich” into 1x2-cm pieces.

3. Tape it into place over the viewing hole on the index card along the edges. Do not put tape OVER the hole or small slit.

electrOMagnetic SpectruM Scientists learn much about the world

by splitting things apart. A geol-ogist can split rocks, a botanist can split seeds, and a physicist can split atoms. About the only

thing an astronomer can split is a beam of light, but even that reveals a great deal — from the temperature of a star to the final moments of matter falling into a black hole.

Our eyes perceive the light from a star as a single color. But instruments split the light into its individual wave-lengths or colors. The intensity of each wavelength tells astronomers how hot the star is, what it’s made of, how it’s moving, and whether it has compan-ions, like other stars or even planets.

Visible light is just one of the forms of energy that make up the electromag-netic spectrum. Other forms include infrared and radio waves, which have a longer wavelength than visible light, and ultraviolet, X-rays, and gamma rays, which are shorter than light.

Telescopes on the ground or in space detect these forms of energy and split them into their component wavelengths, too. Each type of energy tells us about the environment in which it was cre-ated. Infrared, for example, comes from relatively cool objects like gas clouds and planets. And X-rays come from some of the most violent objects in the universe, like disks of hot gas spiraling into black holes.

By splitting each form of energy, astronomers build a more complete understanding of the universe — one wavelength at a time.

Spectroscope

2.5 inpaperclipslit

punchedholes3 in

For 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)

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 puncher

This is the transcript of a StarDate radio episode that aired in July 2004. Script by Damond Benningfield, ©2001, 2004.


ACTiviTyeNGaGeDistribute individual grating cards to the students. Let them look around the room. You may wish to have a light bulb (e.g. 60- 100-watt frosted bulb) or string of holiday lights available.

exPlore With gratings in hand, ask students to look at an incandescent light source (light bulb with a filament) through the grating while holding it close to their eye.

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 are best viewed against a dark background. Ask for alternatives to darkening the room. If necessary, hint at something hand-held, since this instrument should be portable. If no one mentions it, suggest that a tube, with the grat-ing fixed at one end, will block stray light from the view of the spectrum and provide the structural support for the spectroscope components.

What could you use to block out the stray light to make a dark back-ground for viewing spectra?

Attach the grating to one end of a tube. Cut a manila folder in half along the fold. Place a black sheet of construction paper on top of the manila folder half. Roll them together along the long side so that the black paper lines the inside of the tube. Secure with rubber bands or tape.

Attach the grating card to the tube (see figure, right). Fasten a paper clip to one end of the tube, leaving a bit of the clip end over the tube edge. Fas-ten the grating card to the paper clip and secure with a folded card strip.

Have the students look at the incandescent bulb through the tube (with the 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 fluorescent bulb. Does the spectrum of the fluorescent bulb look like that of the incandescent bulb? What is the same or different? (Students should see a continuous spread of color in both bulbs’ spectra. They also may see separate bands of color only in the fluorescent bulb spectrum.)

Finished spectroscope

Paper Clip

Grating card

FoldedStrip


•ContentStandardin9-12PhysicalScience (Interactions of energy andmatter)

•Content Standard in 9-12 Earthand Space Science (Origin and evolutionoftheuniverse)

•ContentStandardin9-12Science and Technology (Abilities of technicaldesign)

sandwich spectrumspectrum


Cover up part of the fluorescent light bulb so that a narrow slit of light is seen. Try making a slit in a double-thick manila folder and holding it in front of the fluorescent source. Compare the incandescent light and the fluorescent light. Do you see color bands now in one of the lights? Which one? Color bands appear dimmer and thinner with the slit in place for the fluorescent bulb. The incandescent bulb has no bands.

Which observing method renders the best detail view of the spectrum fea-ture — with or without the slit? With the slit. There is a limit — if the slit is too narrow, the spectrum appears too faint.

Where is a better place to put the slit, so that an observer can view other light sources? At the opposite end of the tube.

Make an adjustable slit from two index cards. Cut identical rectangular slots, about 1x3 cm, into the center of two index cards. Stack the cards

then fold both cards together along both long sides. The cards should now slide across each other. Adjust the size of the slit by sliding one slot over the other.

Hold the adjustable slit at the opposite end of the tube from the grating and open and close it until you find a position that shows detail and still allows enough light through to see the spectrum clearly. Rotate it if necessary so that the spectrum

has its largest height. This insures the parallel grooves in the grating run in the same direction as the slit.

Congratulations! You have constructed a working spectroscope.

exPlaiN This is a transmission grating. Its surface is scored or etched with thou-sands of parallel grooves per centimeter. As light travels through the nar-row grooves, diffraction effectively turns each groove into a new source of light. As the light spreads out, it interacts or interferes with light of the same wavelength from other grooves. Sometimes the light waves reinforce each other (constructive interference), other times they cancel out and become invisible (destructive interference). Collectively, the constructive interference pattern directs a particular color along a unique angle from the grating. The result is a color spectrum. That’s why blue light appears closest to the image of the source, while red is farthest away. Along those angles, 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 easily seen. It also acts as a structure to attach the grating. The slit allows the wavelengths (colors) of light to be resolved. The diffraction grating is allowing 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 pair of lines in what appeared as a single emission feature viewed through a


tecHNical Notes For cHeMistrY/PHYsics teacHers

•Thisactivityfitswellwithyourexploration of atomic structure, spectra of various elements, how spectra vary for isotopes, and Kirchhoff’slaws.

wide slit. But as the slit narrows, less light passes through. So an observer must strike a balance between the spectrum’s resolution and brightness.

The incandescent light has a hot filament which produces a continuous spectrum (hot liquids also produce continuous spectra). The fluorescent light is made of a tube of hot gas which produces an emission spectrum — more energy is released at certain wavelengths than at others so those colors are more distinct. Which wavelengths are produced depends upon the nature of the gas within a tube. Each gas has its own “fingerprint” or pattern of wavelengths. In a fluorescent light, the gas is mercury.

[For some grade levels, the above explanation is too technical; the teacher may wish to demonstrate constructive and destructive interference with water waves.]

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 the bulb by itself or from the fluorescent bulb. (The Glo-Doodler absorbs cer-tain wavelengths, which show as black bands in the spectrum.)

Think of a safe way to view the spectrum of the Sun — DON’T LOOK AT THE SUN DIRECTLY!! For instance, point the spectroscope at brightly lit clouds or the full Moon (which shines by reflected sunlight). What type of spectrum does the Sun produce? (The Sun produces an absorption spec-trum. The Sun’s photosphere, the solar layer where the Sun radiates most of its light, is cooler than deeper solar layers. The hotter, deeper layers of the Sun act like the light bulb filament while the photosphere acts like the Glo-Doodler. Atomic elements in the photosphere selectively absorb certain wavelengths of light. The resulting spectrum shows the absorbed wave-lengths as diminished bands, or lines, as astronomers call them.)

Scientists use spectroscopes to safely explore any heated object, from the surface of the Sun to a chemical heated by a flame. How could a scientist determine what elements may exist in the Sun’s photosphere? What pro-cess would you suggest?

The spectroscope that the students construct in this activity does not allow for direct measurement of wavelengths. Based on their knowledge of spec-troscope construction and their observations of spectra, ask students how they would improve their spectroscope. Could it allow an observer to mea-sure the 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 the main parts: slit, tube, and grating or prism. Early spectroscopes used a prism instead of a grating.

A portion of our Sun’s spectrum reveals dark lines representing specific elements present in the Sun’s atmosphere.

no

ao

/nsf


studeNt PaGeA galaxy is a gravitationally bound system of stars, gas, and dust. Gal-axies range in diameter from a few thousand to a few hundred thou-sand light-years. Each galaxy contains billions (10 9) or trillions (1012) of stars. In this activity, you will apply concepts of scale to grasp the distances between stars and galaxies. You will use this understanding to elaborate on the question, Do galaxies collide?

exPloreOn a clear, dark night, you can see hundreds of bright stars. The next table shows some of the brightest stars with their diameters and distances from the 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. One light-year equals 9.46 x 1015 meters, and the Sun’s diameter is 1.4 x 109 meters.

Star (Constellation)

Diameter (Sun=1)

Distance (light-years)

Scaled Distance(distance÷diameter)

Spica (Virgo) 8 261

Betelgeuse (Orion) 600 489

Deneb (Cygnus) 200 1,402

Altair (Aquila) 2 17

Vega (Lyra) 2.7 26

Sirius (Canis Major) 1.6 8.6

There are three galaxies beyond the Milky Way that you can see without optical aid: the Andromeda galaxy, the Small Magellanic Cloud, and the Large Magellanic Cloud. Figure the scaled distance to these galaxies (how many times you could fit the galaxy between itself and the Milky Way).

Galaxy Diameter (light-years)

Distance (light-years)

Scaled Distance (distance÷diameter)(no conversion needed)

Milky Way 100,000 0

Andromeda Galaxy 125,000 2,500,000

Large Magellanic Cloud 31,000 165,000

Small Magellanic Cloud 16,000 200,000

exPlaiNHow does the scaled distance of galaxies compare to stars?

elaBorateDo you think galaxies collide? Why or why not?

Stars and GalaxiesSeeing intO the paSt We can’t travel into the past, but we

can get a glimpse of it. Every time we look at the Moon, for example, we see it as it was a little more than a second ago.

That’s because sunlight reflected from the Moon’s surface takes a little more than a second to reach Earth. We see the Sun as it looked about eight minutes ago, and the other stars as they were a few years to a few centuries ago.

And then there’s M31, the Androm-eda galaxy — the most distant object that’s readily visible to human eyes. This great amalgamation of stars stands almost directly overhead late this eve-ning. When viewed from a dark sky-watching location, far from city lights, it looks like a faint, fuzzy blob. But that blob is the combined glow of hundreds of billions of stars — seen as it looked more than two million years ago.

Andromeda is like a larger version of our own Milky Way galaxy. It’s a flat disk that spans more than a quarter-mil-lion light-years. Its brightest stars form spiral arms that make the galaxy look like a pinwheel. Yet the galaxy is so far away that its structure is visible only through telescopes.

The light from M31 has to travel about two and a half million light-years to reach us — about 15 quintillion miles — the number 15 followed by 18 zeroes. Yet even across such an enormous gulf, the galaxy is so bright that we can see it — faintly — with our own eyes, crossing high overhead late tonight.

This is the transcript of a StarDate radio episode that aired October 14, 2006. Script by Damond Benningfield, ©2006.


teacHer lessoN KeY

oBjectiVesCalculate 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 circum-ference (such as a water bottle, tennis ball, or soda can). We will use a tennis ball 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 the other? In other words, how many tennis balls across is the table?” Accept all answers. Then find the answer in front of the class by moving the ball across the table one space at a time, counting each move out loud.

exPlore (aNswers)


•ContentStandardin9-12Scienceas Inquiry (Understanding about scientificinquiry)

•Content Standard in 9-12 Earthand Space Science (Origin and evolutionoftheuniverse)

Stars To convertDistance (ly) x 9.46 x 1015 (m/ly) Diameter (Suns) x 1.4 x 109 (m/Sun)

Scaled DistanceDistance÷Diameter

(both must be in the same units, do conversions first)

Spica (Virgo) 2.22 x 108

Betelgeuse (Orion) 5.51 x 106

Deneb (Cygnus) 4.74 x 107

Altair (Aquila) 5.74 x 107

Vega (Lyra) 6.51 x 107

Sirius (Canis Major) 3.59 x 107

GalaxiesDistance÷Diameter(no conversion needed)

Scaled Distance from Milky Way

Distance÷Diameter(no conversion needed)

Milky Way ------

Andromeda Galaxy 20

Large Magellanic Cloud 5.32

Small Magellanic Cloud 12.5

exPlaiNHow does the scaled distance of galaxies compare to stars?

Galaxies, compared to their size, are much closer together than stars. Neigh-boring stars are usually millions of star-diameters apart, while galaxies are usually 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 the combined mass of billions of stars. So even over large distances, the attraction between galaxies can accelerate them toward each other. Thick of bowling balls (galaxies) versus sand grains (stars) on a trampoline (space). The galaxies stretch and distort the trampoline much more, and over a wider area, than do single stars. Even though galaxies collide, the stars within galaxies seldom collide because they are so far away from each other. Clouds of gas and dust in the galaxies do collide, though, giving birth to new stars.

eValuate Rubric: Explore = 60 pts (6 pts for each calculation), Explain = 25 pts, Elaborate = 15 pts


In 2006, Hubble Space Telescope aimed at a nearby collection of galaxies called the Coma Cluster. Using the HST images, astronomers gained fascinating insights into the evolution of galaxies in dense galactic neighborhoods. In this activity, students will first learn the basics of galaxy classification and grouping, then use HST images to discover the “morphology-density effect” and make hypotheses about its causes.

Materials & PreParatioN

Each student needs a copy of the next 7 pages (not this page). You may • copy the pages out of this guide, but it is recommended that you go to mcdonaldobservatory.org/teachers/classroom and download the student worksheets. The galaxy images in the online worksheets are “negatives” of the real images, which provides better detail when printing. Supple-mental materials for this activity are also available on the website.

Each student or student team will need a calculator and a magnifying • glass (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 interpreta-tion.

Page 36 (30 pts):• Graded for completion, not accuracy. Students will get different numbers, but math should be correct. Answers for percentages are 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). Students usually find a higher percentage of spirals in the field.

Page 37 (bottom, 30 pts):• Student hypothesis should mention the effects of interactions and ram-pressure stripping in changing past gas-rich spirals into current gas-poor ellipticals and lenticulars in clusters.

Coma Cluster of GalaxiesNatioNal scieNce educatioN staNdards

•ContentStandardin9-12ScienceasInquiry (Abilities necessary to do sci-entific inquiry, Understanding about scientificinquiry)

•Content Standard in 9-12 Earth andSpace Science (Origin and evolution oftheuniverse)

inviSible cluSterIf you aim a big telescope at the Coma

Cluster, you’ll see galaxies galore — thousands of galaxies of all sizes and shapes, from little puffballs to

big, fuzzy footballs. Even so, you won’t see most of the cluster because it’s invis-ible to human eyes.

Some of the cluster’s “dark side” is in the form of superhot gas that glows in X-rays. All together, the gas is several times as massive as the galaxies themselves.

There’s a dynamic interplay between the hot gas and the galaxies.

As galaxies “fall” toward the center of the cluster, they fly through the hot gas, which strips away the cold gas inside the galaxies. Without their cold gas, the galaxies can’t give birth to new stars. That helps transform the appearance of some of the galaxies. Spiral galaxies lose their spiral arms, so they look like featureless disks.

But the galaxies may have an effect on the hot gas, too. Over the eons, it should have cooled, but it hasn’t. Hot “jets” of particles from the centers of some galax-ies may act like big blowtorches, keeping the gas hot.

Yet even the gas and the galaxies com-bined make up only a small fraction of the Coma Cluster. As much as 80 percent of its mass may consist of dark matter — a form of matter that produces no detectable energy, but that exerts a gravitational pull on the visible matter around it. The dark matter ensures that most of this impressive cluster remains invisible.

This is the transcript of a StarDate radio episode that aired May 6, 2008. Script by Damond Benningfield, ©2008.


eNGaGeThe diagram above shows a mosaic of 40 galaxies. These images were taken with Hubble Space Telescope and show the variety of shapes that galaxies can assume. When astronomer Edwin Hubble first started studying these vari-ous types of galaxies in the 1920s, he realized he needed to develop a way to organize and categorize them. He cre-ated a classification scheme in which he grouped similar galaxies together. Your job is to do the same thing. In the chart, invent your own four galaxy types and provide a description and three examples for each one.

Galaxy Type(name and draw)

Defining Characteristics (write a short description, provide enough detail so that anyone could use your scheme)

Three Examples (give 3 grid coordinates)

gem

s C

oll

aBo

rat

ion


exPloreThe image on the left is the classification scheme that Hubble himself came up with. He thought that the “tuning fork” sequence represented the

evolutionary progression of galaxies. This concept turned out to be wrong, although astronomers still use these

general categories and labels to describe galaxies.

tHe MaiN GalaxY tYPes

Elliptical (E):• Spherical or elliptical shape (like a football), has no flat disc or spiral arms

Lenticular (S0):• Smooth, flat disk shape with-out spiral structure, often hard to distinguish

from ellipticals

Barred Lenticular (SB0):• Same as above, but with an elongated (barred) nucleus

Spiral (S):• Flat disk shape with notable spiral patterns in the outer disk, also contains a large bright

central bulge

Barred Spiral (SB):• A special type of spiral characterized by an elongated nucleus with the spiral arms springing from the ends of the bar

There are two other categories for classifying galaxies:

• Irregular (IR): An oddly shaped galaxy that doesn’t fit into any other category

• Interacting (INT): Two or more galax-ies that are so close together that they are affecting each other’s shape

Using the definitions above, place the 12 gal-axies on the left into their proper morphol-ogy categories:

Morphology Picture Numbers (3 each)

E/S0/SB0

S

SB

IR

The smallest galaxies are often called dwarf galaxies (No. 5 and No. 7 are dwarf galax-ies). These contain only a few billion stars — a small number compared to the Milky Way’s 200 billion. The largest ellipticals con-tain several trillion stars.

1 2 3

4 5 6

7 8 9

10 11 12

ORDINARY SPIRALS

BARRED SPIRALS

ELLIPTICAL GALAXIES

Boxy Disky SBO

SO

SBa SBb SBcIBm

ImSaSb

Sc

IRR

EG

UL

AR

S

eso

(to

P r

igH

t);

all

ot

Her

s n

asa

JoH

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tHe coMa GalaxY clusterThe Coma Cluster, which is centered about 320 million light-years away, contains several thousand individual galaxies. The cluster has a roughly spherical shape and is about 20 million light-years across. (For compari-son, the Milky Way is 100,000 light-years across). That many galaxies in a relatively small space makes the Coma Cluster one of the richest and densest galaxy clusters in our region of the universe.

On the following pages you will be asked to count different types of galaxies. Use the labels on this picture as an example of how to count the various objects.

I) Ellipticals or Lenticulars

It can be hard to tell these apart. If you know it’s either an E or S0/SB0, it is okay to guess between these two.

II) Spirals and Barred Spi-rals

It can be hard to tell these apart. If you know it’s either an S or SB, it is okay to guess between these two.

III) Irregular galaxy

IV) Uncertain

An edge-on view of a gal-axy that could possibly be an S0, SB0, S, SB, or IR. There are too many pos-sibilities, so do not count these.

Star)

Any object that has “crosshairs” sticking out of it is a foreground star in the Milky Way galaxy, so do not count these.

?)

Don’t count small, faint objects like these that are too hard to classify.

NWW

Arcturus

COMA BERENICESBIG DIPPER

I ?

?

?

I

I

I

I

II

II

Star

II

I

I

IV III

??

II

II

StarStar

IV IV

na

sa/s

tsc

i/Co

ma

Hst

aC

s t

rea

sUry

tea

m (

3)t

im Jo

nes


E S0 /SB0 S SB IR / INT

Top Image (A)

Bottom Image (B)

Count the number of galaxies of each morphological type and write down the number in the correct spot in the table. Use the guidelines on page 4 to help you decide which objects to count.

A

B


E S0 /SB0 S SB IR / INT

Top Image (C)

Bottom Image (D)

Count the number of galaxies of each morphological type and write down the number in the correct spot in the table. Use the guidelines on page 4 to help you decide which objects to count.

C

D

na

sa/s

tsc

i/Co

ma

Hst

aC

s t

rea

sUry

tea

m (

4)


exPlaiN Galaxies 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 edge of 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 visible universe, and many more beyond that. Galaxies live in a variety of envi-ronments. Sometimes large numbers of them are packed close together in clusters, such as the Coma Cluster; sometimes they gather in smaller num-bers called groups, like the Local Group that contains our Milky Way; and sometimes they are isolated far from one another in the field.

Number of Galaxies

Minimum Number of Non-dwarf

Galaxies

Diameter (1 Mpc = 3.26

million light years)Total Mass

Galaxy ClusterLarge and dense 50 to thousands 6 2 to 10 Mpc 1014 to 1015

solar masses

Galaxy GroupSmall and dense less than 50 3 1 to 2 Mpc 1013 solar

masses

The FieldLarge and deserted very few 0 Voids, can be larger

than 100 Mpc < 1010

Clusters, groups, and some isolated galaxies can all be part of even larger structures called superclusters. At the largest scales in the visible universe, superclusters are gathered into filaments and walls surrounding vast voids, often described as resembling large soap bubbles. This structure often is referred to as the “cosmic web.”

On the previous two pages, the images on the top (A&C) show the dense central 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 numbers you wrote down on the previous two pages:

Morphology→E

EllipticalsS0 & SB0Lenticulars

S & SB (sum both together) Regular and Barred Spirals

Total(E+S0+SB0+S+SB)

Image A

Image C

Sum Total From A + C (e) (f) (g) (h)

Image B

Image D

Sum Total From B + D (i) (j) (k) (m)

i—mi—mj—mj—mk—mk—m

Using a calculator, find the percentages of each galaxy type in the cluster versus

the field (ignore IRs and INTs). Fill in each of the boxes on the right:

Where did you find a higher percentage of spirals — in the Cluster or in the Field? Answer: _________________________

The percentages that you just found tell us which types of galaxies are common in the Coma Cluster versus which types are common in the field. Astronomers have done this same exercise on hundreds of thousands of galaxies in the nearby universe, and discovered that the following percent-ages are pretty typical:

In dense clusters, 40 percent of the galaxies are ellipticals, 50 percent • are lenticulars, and 10 percent are spirals.

In the field, 10 percent of the galaxies are ellipticals, 10 percent are len-• ticulars, and 80 percent are spirals.

When galaxies are found very close together there are more ellip-ticals and lenticulars. When galaxies are far apart there are more spirals. Astronomers call this the “morphology-density effect” (the word morphology means “type” or “class,” not “transformation,” as in biology). The term basically means that in crowded galaxy neighborhoods, like clus-ters, there are different types of galaxies than are found in open areas, like the field.

exteNdThe clues needed to answer the last question are in the following para-graphs. Please read the paragraphs carefully and then answer the question at the right.

As a general rule, spiral galaxies (S and SB) have a lot of gas and are still forming 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-rich Both Ellipticals and Lenticulars are Gas-poor

Galaxies that are very close to each other, such as those in clusters, often undergo many violent interactions with each other. When a gas-rich spiral galaxy interacts with another galaxy, it tends to quickly use up most of its gas to make new stars, leaving little gas behind. Galaxy-galaxy interactions often change gas-rich galaxies into gas-poor galaxies. Many lenticular galaxies are the remains of old spirals that have lost their gas, and many elliptical galaxies are the remains of several spiral galaxies that have collided.

Galaxy clusters are usually filled with a lot of extremely hot gas that is spread between galaxies throughout the cluster. However, there is no hot gas like this out in the field. When the radiation from this hot gas hits a spiral galaxy, it strips the spiral galaxy of its much cooler gas in a process called ram-pressure stripping. This process quickly converts a gas-rich spiral galaxy into a gas-poor lenticular galaxy. Spiral galaxies have a hard time surviving in the superheated gas environment.


Using what you’ve learned, write a hypothesis that might explain why we see the morphology-density effect. In other words, why do we see more elliptical and lenticular galaxies in clusters and more spiral galaxies in the field? Remem-ber that galaxies change and evolve over time, and these galaxies have had a very long time to get to this point.


Printed materialsStarDate magazine 1-800-STARDATE stardate.org/magazine

StarDate: The Solar System 1-800-STARDATE stardate.org/resources/ssguide

StarDate: Beyond the Solar System 1-800-STARDATE stardate.org/resources/btss

The Universe at Your Fingertips Astronomical Society of the Pacific, 1995 ISBN 1-886733-00-7 www.astrosociety.org

El Universo a Sus Pies Astronomical Society of the Pacific, 2002 ISBN 1-58381-199-0 www.astrosociety.org

Observer’s Handbook (for advanced stargazers) Royal Astronomical Society of Canada www.rasc.ca

Princeton Field Guides: Stars & Planets, 4th ed. by Ian Ridpath and Wil Tirion, 2007 ISBN 978-0-691-13556-4

The Young Oxford Book of Astronomy by Simon and Jacqueline Mitton, 1995 ISBN 0-19-521169-3

Unfolding our Universe by Iain Nicolson, 1999 ISBN 0521-59270-4

National Science Education Standards National Research Council, 1996 ISBN 0309053269 www.nap.edu/html/nses/html

The Solar System: A Firefly Guide by Giovanni Caprara, 2003 ISBN 10: 1552976793

ResourcesThe Stars: A New Way to See Them by H. A. Rey, 1976 ISBN 0395245087

Nearest Star: The Surprising Science of our Sun by Leon Golub and Jay M. Pasachoff, 2001 ISBN 0-674-00467-1

Cambridge Encyclopedia of the Sun by Kenneth R. Lang, 2001 ISBN 0-521-78093-4

Galaxies in Turmoil by Chris Kitchin, 2007 ISBN 1-84628-670-0

Lawrence Hall of Science: Great Explorations in Math and Science www.lawrencehallofscience.org/gems

audioStarDate radio 1-800-STARDATE stardate.org/radio

Universo radio 1-800-STARDATE radiouniverso.org/radio/

internetStarDate Online stardate.org

Universo Online radiouniverso.org

McDonald Observatory Visitors Center mcdonaldobservatory.org

National Science Teachers Association www.nsta.org

NASA www.nasa.gov

Powers of Ten powersof10.com

NASA resources for sale education.nasa.gov/edprograms/core/home/

NASA Education Resources education.nasa.gov

AAS Education Resources www.aas.org/education/EducatorResources.php

ASP Education Resources www.astrosociety.org/education.html

Spanish Language Astronomy Materials Center www.astronomyinspanish.org

Galaxies and Cosmos Explorer www.as.utexas.edu/gcet

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