THE LIFE AND DEATH OF
BOB (a.k.a. NGC 6397) IN
AN INTRODUCTORY
COLLEGE-LEVEL
ASTRONOMY COURSE
Dr. C. Renee James NASA Top Stars 2010
Hmmm…what would be a good way
to start an introductory stars and
galaxies class for non-science majors
at a state university?
Lots of equations?!?
perhaps not
Pretty pictures?
that’d probably
work, but there are
so many…
Dr. C. Renee James NASA Top Stars 2010
I know! I’ll just scour the Hubble Heritage
Site for something cool-looking that relates to
stars and galaxies.
Dr. C. Renee James NASA Top Stars 2010
Okay…I just spent four hours
looking at a jillion cool photos.
Perhaps I should start smaller.
Maybe with the “stars” part of
“stars and galaxies.”
Aha! Here’s one...
Dr. C. Renee James NASA Top Stars 2010
My new friend: NGC 6397
http://heritage.stsci.edu/2003/21/index.html
• Good colors. Not too
complicated looking.
Stars have a variety
of obvious
differences. Plus
globular clusters
might come in handy
later this semester.
Sure…I’ll start with
this one, but how?
Dr. C. Renee James NASA Top Stars 2010
What does the education research say?
• Let the students ask the questions. (inquiry-based learning)
• Let the students work together to find the answers.
(collaborative learning)
• Just a few of the references on the subject (in 3 point font –
see end of show for a more legible version)
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Klein, C. 1982, Children's Concepts of the Earth and the Sun: A Cross-Cultural Study, Science Education, 65, 95.
Abell, S., George, M., & Martini, M. 2002, The Moon Investigation: Instructional Strategies for Strategies for Elementary Science Methods, Journal of Science Teacher Education, 13(2), 85.
Lightman, A., & Sadler, P. M. 1988, The Earth Is Round? Who Are You Kidding?, Science and Children, 25(5), 24.
Abell, S., Martini, M., & George, M. 2001, 'That's What Scientists Have To Do': Preservice Elementary Teachers' Conceptions of the Nature of Science During a Moon Investigation, International Journal of Science Education, 23(11), 1095.
Lightman, A., & Sadler, P. M. 1993, Teacher Predictions Versus Actual Student Gains, The Physics Teacher, 31, 162.
Lindell, R. S. 2001, Enhancing College Students' Understanding of Lunar Phases, Unpublished doctoral dissertation, University of Nebraska, Lincoln.
Adams, J. P., & Slater, T. F. 1998, Mysteries of the Sky: Activities for Collaborative Groups, Dubuque, IA: Kendall Hunt Publishing, 1998a.
Lindell, R. S., & Olsen, J. P. 2002, Developing the Lunar Phases Concept Inventory, Paper presented at the American Association of Physics Teachers Summer Meeting (Physics Education Research Conference), August, Boise, ID.
Adams, J. P., & Slater, T. F. 1998, Using Action Research To Bring the Large Lecture Course Down to Size, Journal of College Science Teaching, 28, 87, 1998b.
Mali, G., & Howe, A. 1979, A Development of Earth and Gravity Concepts Among Nepali Children, Science Education, 63, 685.
Adams, J. P., & Slater, T. F. 2002, Learning Through Sharing: Supplementing the Astronomy Lecture with Collaborative-Learning Group Activities, Journal of College Science Teaching, 31, 384.
Mallon, G. L., & Bruce, M. H. 1982, Student Achievement and Attitudes in Astronomy: An Experimental Comparison of Two Planetarium Programs, Journal of Research in Science Teaching, 19, 53.
Adams, J. P., & Slater, T. F. 2000, Astronomy in the National Science Education Standards, Journal of Geoscience Education, 48, 39.
Maran, S. P. 2000, 'Hot Topics' in Astrophysics, The Physics Teacher, 38, 550.
Adams, J. P., Brissenden, G., Lindell, R. S., Slater, T. F., & Wallace, J. 2002, Observations of Student Behavior in Collaborative Learning Groups, Astronomy Education Review, 1(1), 25. http://aer.noao.edu/AERArticle.php?issue=1&section=1&article=2.
Morrow, C. A. 2003, Misconceptions scientists often have about the K–12 National Science Education Standards, Astronomy Education Review, 1(2), 84. http://aer.noao.edu/AERArticle.php?issue=2&section=2&article=8.
National Research Council. 1996, National Science Education Standards, Washington, D.C.: National Academy Press.
Adams, J. P., Prather, E. E., & Slater, T. F. 2002, Lecture-Tutorials for Introductory Astronomy, Preliminary Ed., Upper Saddle River, NJ: Prentice Hall.
National Research Council. 1999, How People Learn: Brain, Mind, Experience, and School, Washington, D.C.: National Academy of Sciences.
Albanese, A., Danhoni Neves, M. C., & Vicentini, M. 1997, Models in Science and in Education: A Critical Review of Research on Students' Ideas About the Earth and Its Place in the Universe, Science and Education, 6, 573.
Nussbaum, J. 1979, Children’s Conception of the Earth as a Cosmic Body: A Cross Age Study, Science Education, 63, 83.
American Association for the Advancement of Science Project 2061. 1993, Benchmarks for Science Literacy, New York: Oxford University Press.
Nussbaum, J., & Novak, J. 1976, An Assessment of Children’s Concepts of the Earth Utilizing Structured Interviews, Science Education, 60, 535.
Ashcraft, P., & Courson, S. 2003, Effects of an Inquiry-Based Intervention to Modify Pre-Service Teachers' Understanding of Seasons, Paper presented at the Annual Meeting of theNational Association for Research in Science Teaching, March, Philadelphia, PA.
Nussbaum, J., & Sharoni-Dagan, N. 1983, Changes in Second Grade Children’s Preconceptions About the Earth as a Cosmic Body Resulting from a Short Series of Audio-Tutorial Lessons, Science Education, 67, 99.
Atwood, R. K., & Atwood, V. A. 1996, Preservice Elementary Teachers' Conceptions of the Causes of Seasons, Journal of Research in Science Teaching, 33, 553.
Offerdahl, E. G., Prather, E. E., & Slater, T. F. 2002, Students’ Pre-Instructional Beliefs and Reasoning Strategies About Astrobiology Concepts, Astronomy Education Review, 1(2), 5. http://aer.noao.edu/AERArticle.php?issue=2&section=2&article=1.
Parker, J., & Heywood, D. 1998, The Earth and Beyond: Developing Primary Teachers' Understanding of Basic Astronomical Events, International Journal of Science Education, 20, 503.
Atwood, V. A., & Atwood, R. K. 1995, Preservice Elementary Teachers' Conceptions of What Causes Night and Day, School Science and Mathematics, 95, 290.
Pasachoff, J. M. 2001, What Should Students Learn?, The Physics Teacher, 39, 381.
Bailey, J. M. 2000, On the Nature of Moonquakes, The Physics Teacher, 38, 522.
Pasachoff, J. M. 2002, Pasachoff's Points, The Physics Teacher, 40, 197, 2002a.
Baker, B., & Heruth, D. 2000, An Interdisciplinary Approach to Stargazing, The Physics Teacher, 38, 555.
Pasachoff, J. M. 2002, What Should College Students Learn? Phases and Seasons? Is Less More or Is Less Less?, Astronomy Education Review, 1(1), 124. http://aer.noao.edu/AERArticle.php?issue=1&section=4&article=3, 2002b.
Ball, N., Coyle, H. P., & Shapiro, I. I. (Eds.). 1994, Project SPICA: A Teacher Resource to Enhance Astronomy Education, Dubuque, IA: Kendall-Hunt Publishing.
Prather, E. E., Slater, T. F., & Offerdahl, E. G. 2002, Hints of a Fundamental Misconception in Cosmology, Astronomy Education Review, 1(2), 28. http://aer.noao.edu/AERArticle.php?issue=2&section=2&article=2.
Barba, R., & Rubba, P. A. 1992, A Comparison of Preservice and In-Service Earth and Space Science Teachers' General Mental Abilities, Content Knowledge, and Problem-Solving Skills, Journal of Research in Science Teaching, 29, 1021.
Reed, G., & Campbell, J. R. 1972, A Comparison of the Effectiveness of the Planetarium and the Classroom Chalkboard and Celestial Globe in the Teaching of Specific Astronomical Concepts, School Science and Mathematics, 72, 368.
Roettger, E. E. 1998, Changing View of the Universe, Paper presented at the American Association of Physics Teachers Winter Meeting, January, New Orleans, LA.
Barnett, M., & Morran, J. 2002, Addressing Children's Alternative Frameworks of the Moon's Phases and Eclipses, International Journal of Science Education, 24(8), 859.
Sadler, P. M. 1992, The Initial Knowledge State of High School Astronomy Students, Unpublished doctoral dissertation, Harvard University, Cambridge, MA.
Baxter, J. 1989, Children's Understanding of Familiar Astronomical Events, International Journal of Science Education, 11, 502.
Sadler, P. M. 1998, Psychometric Models of Student Conceptions in Science: Reconciling Qualitative Studies and Distractor-Driven Assessment Instruments, Journal of Research in Science Teaching, 35(3), 265.
Bieniek, R. J., & Zeilik, M. 1976, Follow-up Study of a PSI Astronomy Course, American Journal of Physics, 44(7), 695.
Sadler, P. M. 2001, Choosing Between Teaching Helioseismology and Phases of the Moon, The Physics Teacher, 39, 554.
Bisard, W. J., Aron, R. H., Francek, M. A., & Nelson, B. D. 1994, Assessing Selected Physical Science and Earth Science Misconceptions of Middle School Through University Preservice Teachers: Breaking the Science 'Misconception Cycle', Journal of College
Science
Teaching,
24, 38.Discussion, The Physics Teacher, 40, 198.
Sadler,
P. M.
2002, Further
Bishop, J. E. 1977, United States Astronomy Education: Past, Present, and Future, Science Education, 61, 295.
Safko, J. L. 1998, Self-Paced Astronomy at the University of South Carolina—A Twenty-Five Year Retrospect, Poster session presented at the American Association of Physics Teachers Winter Meeting, New Orleans, LA.
Samarapungavan, A., Vosniadou, S., & Brewer, W. F. 1996, Mental Models of the Earth, Sun, and Moon: Indian Children's Cosmologies, Cognitive Development, 11(4), 491.
Bobrowsky, M. 2000, Teaching Evolutionary Processes to Skeptical Students, The Physics Teacher, 38, 565.
Schneps,
M.
P.
1989,
A
Private Universe, Video. San Francisco: Astronomical Society of the Pacific.
Brickhouse, N. W., Dagher, Z. R., Letts IV, W. J., & Shipman, H. L. 2000, Diversity of Students' Views About Evidence, Theory, and the Interface Between Science and Religion in an Astronomy Course, Journal of Research in Science Teaching, 37(4), 340.
Schoon, K. J. 1992, Students’ Alternative Conceptions of Earth and Space, Journal of Geological Education, 40(3), 209.
Brickhouse, N. W., Dagher, Z. R., Shipman, H. L., & Letts IV, W. J. 2002, Evidence and Warrants for Belief in a College Astronomy Course, Science and Education, 11(6), 573.
Shawl, S. J. 2000, 'It’s ONLY a Theory': What Do Students Know About the Scientific Enterprise?, Poster session presented at the 195th Meeting of the American Astronomical Society, January, Atlanta, GA.
Brissenden, G. 2001, SABER Astronomy Online Database: Searchable Annotated Bibliography of Education Research, Retrieved February 15, 2002, from http://www.cdes-astro.com/saber/index.htm.
Skala, C., Slater, T. F., & Adams, J. P. 2000, Qualitative Analysis of Collaborative Learning Groups in Large Enrollment Introductory Astronomy, Publications of the Astronomical Society of Australia, 17, 185.
Callison, P. L., & Wright, E. L. 1993, The Effect of Teaching Strategies Using Models on Preservice Elementary Teachers' Conceptions About Earth-Sun-Moon Relationships, Paper presented at the Annual Meeting of the National Association for Research in Science
Skam, K.Teaching,
1994, Determining
April, Atlanta,
Misconceptions
GA.
About Astronomy, Australian Science Teachers Journal, 40(3), 63.
Slater, T. F. 2000, K-12 Astronomy Benchmarks from Project 2061, The Physics Teacher, 38, 538.
Casey, T. L., & Slater, T. F. 2002, A Comparison of Group and Individually Completed Course Evaluations in Introductory Astronomy, Astronomy Education Review, 1(2), 1. http://aer.noao.edu/AERArticle.php?issue=2&section=2&article=3.
Slater, T. F., & Adams, J. P. 2002, Mathematical Reasoning over Arithmetic in Introductory Astronomy, The Physics Teacher, 40, 268.
Comins, N. F. 2000, A Method To Help Students Overcome Astronomy Misconceptions, The Physics Teacher, 38, 542, 2000a.
Slater, T. F., & Adams, J. P. 2003, Learner-Centered Astronomy: Strategies for Teaching ASTRO 101, Upper Saddle River, NJ: Prentice Hall.
Comins, N. F. 2000, An In-Your-Face Approach to Student Misconceptions About Astronomy, Unpublished manuscript, 2000b.
Slater, T. F., Adams, J. P., Brissenden, G., & Duncan, D. 2001, What Topics are Taught in Introductory Astronomy Courses?, The Physics Teacher, 39, 52.
Comins, N. F. 2001, Heavenly Errors: Misconceptions About the Real Nature of the Universe, New York: Columbia University Press.
Slater, T. F., Carpenter, J. R., & Safko, J. L. 1996, Dynamics of a Constructivist Astronomy Course for In-Service Teachers, Journal of Geoscience Education, 44, 523.
DeLaughter, J. E., Stein, S., Stein, C. A., & Bain, K. R. 1998, Preconceptions Abound Among Students in an Introductory Earth Science Course, EOS Transactions, 79, 429.
Slater, T. F., Jones, L. V., Bailey, J. M., Jaeggli, S. A., & Lee, A. C. 2003, An Online Interactive Astronomy Course for Non-Science Majors, Poster session presented at the 201st Meeting of the American Astronomical Society, January, Seattle, WA.
Slater, T. F., Prather, E. E., Bailey, J. M., & Adams, J. P. 2003, Effectiveness of a Lecture-Tutorial Approach to Large Enrollment Introductory Astronomy, Paper presented at the Annual Meeting of the National Association for Research in Science Teaching, March, Philadelphia, P
Deming, G., & Hufnagel, B. 2001, Who's taking ASTRO 101?, The Physics Teacher, 39, 368.
Slater, T. F., Safko, J. L., & Carpenter, J. R. 1999, Long-Term Attitude Sustainability from a Constructivist-Based Astronomy-for-Teachers Course, Journal of Geoscience Education, 47, 366.
diSessa, A. 1993, Toward an Epistemology of Physics, Cognition and Instruction, 10, 105.
Sneider, C. I., & Ohadi, M. M. 1998, Unraveling Students' Misconceptions About the Earth's Shape and Gravity, Science Education, 82(2), 265.
Dunlop, J. 2000, How Children Observe the Universe, Publications of the Astronomical Society of Australia, 17, 194.
Sneider, C. I., & Pulos, S. 1983, Children's Cosmographies: Understanding the Earth's Shape and Gravity, Science Education, 67(2), 205.
Fanetti, T. M. 2001, The Relationships of Scale Concepts on College Age Students' Misconceptions About the Cause of Lunar Phases, Unpublished master's thesis, Iowa State University, Ames.
Stahly, L. L., Krockover, G. H., & Shepardson, D. P. 1999, Third Grade Students' Ideas About the Lunar Phases, Journal of Research in Science Teaching, 36(2), 159.
Finegold, M., & Pundak, D. 1990, Students' Conceptual Frameworks in Astronomy, Australian Science Teachers Journal, 36, 76.
Treagust, D. F., & Smith, C. L. 1989, Secondary Students' Understanding of Gravity and the Motion of Planets, School Science and Mathematics, 89(5), 380.
Trumper, R. 2000, University Students' Conceptions of Basic Astronomy Concepts, Physics Education, 35(1), 9.
Fletcher, J. K. 1980, Traditional Planetarium Programming Versus Participatory Planetarium Programming, School Science and Mathematics, 80, 227.
Trumper, R. 2001, A Cross-Age Study of Junior High School Students' Conceptions of Basic Astronomy Concepts, International Journal of Science Education, 23(11), 1111, 2001a.
Fraknoi, A. 1998, Astronomy Education: A Selective Bibliography, Retrieved April 6, 2003, from http://www.astrosociety.org/education/resources/educ_bib.html.
Trumper, R. 2001, A Cross-Age Study of Senior High School Students' Conceptions of Basic Astronomy Concepts, Research in Science and Technological Education, 19(1), 97, 2001b.
Fraknoi, A. 2002, Enrollments in Astronomy 101 Courses: An Update, Astronomy Education Review, 1(1), 121. http://aer.noao.edu/AERArticle.php?issue=1&section=4&article=2.
Trumper, R. 2001, A Cross-College Age Study of Science and Nonscience Students' Conceptions of Basic Astronomy Concepts in Preservice Training for High-School Teachers, Journal of Science Education and Technology, 10(2), 189, 2001c.
Gregory, B., Luzader, W. M., & Coyle, H. P. 1995, Project STAR: The Universe in Your Hands, Dubuque, IA: Kendall-Hunt Publishing.
Trundle, K. C., Atwood, R. K., & Christopher, J. E. 2002, Preservice Elementary Teachers' Conceptions of Moon Phases Before and After Instruction, Journal of Research in Science Teaching, 39(7), 633.
Haupt, G. W. 1948, First Grade Concepts of the Moon, Science Education, 32(4), 258.
Trundle, K. C., Atwood, R. K., & Christopher, J. E. 2003, Preservice Elementary Teachers' Conceptions of Moon Phases: A Longitudinal Study, Paper presented at the Annual Meeting of the National Association for Research in Science Teaching, March, Philadelphia, PA.
Vosniadou, S., & Brewer, W. F. 1987, Theories of Knowledge Restructuring in Development, Review of Educational Research, 57(1), 51.
Haupt, G. W. 1950, First Grade Concepts of the Moon: Part II: By Interview, Science Education, 34(4), 224.
Vosniadou, S., & Brewer, W. F. 1992, Mental Models of the Earth: A Study of Conceptual Change in Childhood, Cognitive Psychology, 24(4), 535.
Hemenway, M. K., Straits, W. J., Wilke, R. R., & Hufnagel, B. 2002, Educational Research in an Introductory Astronomy Course, Innovative Higher Education, 26(4), 271.
Vosniadou, S., & Brewer, W. F. 1994, Mental Models of the Day/Night Cycle, Cognitive Science, 18(1), 123.
Hufnagel, B. 2002, Development of the Astronomy Diagnostic Test, Astronomy Education Review, 1(1), 47. http://aer.noao.edu/AERArticle.php?issue=1&section=1&article=4.
Wall, C. A. 1973, A Review of Research Related to Astronomy Education, School Science and Mathematics, 73(8), 653.
Hufnagel, B., Slater, T. F., Deming, G., Adams, J. P., Adrien, R. L., Brick, C., & Zeilik, M. 2000, Pre-Course Results from the Astronomy Diagnostic Test, Publications of the Astronomical Society of Australia, 17, 152.
Wandersee, J. H., Mintzes, J. J., & Novak, J. D. 1994, Research on Alternative Conceptions in Science, In Handbook of Research on Science Teaching and Learning, D. L. Gabel (Editor), New York: MacMillan Publishing, 177.
Janke, D. L., & Pella, M. O. 1972, Earth Science Concept List for Grades K–12 Curriculum Construction and Evaluation, Journal of Research in Science Teaching, 9, 223.
Yost, M. 1973, Similarity of Science Textbooks: A Content Analysis, Journal of Research in Science Teaching, 10(4), 317.
Zeilik, M. 1974, A PSI Astronomy Course, American Journal of Physics, 42(12), 1095.
Jones, B. L., Lynch, P. P., & Reesink, C. 1987, Children's Conceptions of the Earth, Sun and Moon, International Journal of Science Education, 9, 43.
Zeilik, M. 1981, Flexible, Mastery-Oriented Astrophysics Sequence, American Journal of Physics, 49(9), 827.
Kikas, E. 1998, The Impact of Teaching on Students' Definitions and Explanations of Astronomical Phenomena, Learning and Instruction, 8, 439.
Zeilik, M. 1998, Interactive Lesson Guide for Astronomy, Revised Ed., Santa Fe, NM: The Learning Zone.
Zeilik, M. 2002, Birth of the Astronomy Diagnostic Test: Prototest Evolution, Astronomy Education Review, 1(2), 46. http://aer.noao.edu/AERArticle.php?issue=2&section=2&article=5.
Zeilik, M., & Bisard, W. J. 2000, Conceptual Change in Introductory-Level Astronomy Courses, Journal of College Science Teaching, 29(4), 229.
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Dr. C. Renee James NASA Top Stars 2010
Sounds reasonable enough…
• My very first “Stars & Galaxies” class ran
in fall 2006.
• After having attended a workshop on
learner-center astronomy during Summer
2006, I was determined to give it a shot.
• I began the semester with the following
slide:
Dr. C. Renee James NASA Top Stars 2010
A jillion points of
light (stars)
What can you tell from just
this picture?
Are all stars the same?
What’s different?
WHAT SPECIFIC
INFORMATION DO YOU
THINK WOULD HELP
YOU UNDERSTAND
MORE ABOUT THESE
STARS?
Dr. C. Renee James NASA Top Stars 2010
First group assignment:
• Name five things that you can tell about
NGC 6397 JUST BY LOOKING AT THIS
PHOTO. Think small (very small) like a child.
Dr. C. Renee James NASA Top Stars 2010
At this point, the class chats.
• I encourage them to exchange contact
information so that they have study
partners.
• I tell them that no observation is too
obvious.
• I warn them that some conclusions cannot
be made on the basis of the photo.
Dr. C. Renee James NASA Top Stars 2010
What the students said:
• You can tell stars are different colors.
• Stars look different sizes or brightnesses.
(at which point I ask if they can really determine size
or absolute brightness)
• Stars are really clumped together in the middle of the
picture.
• Some stars look closer than others.
(at which point I ask if they can really determine
distance)
• Orange stars tend to be brighter and bigger-looking
than white stars.
Dr. C. Renee James NASA Top Stars 2010
Phew – one collaboration down.
Now what? Oh yes…inquiry
based learning.
• I want my students to ‘own’ the class from
the first day, so I let them decide the
direction of class from there with the
following question:
Dr. C. Renee James NASA Top Stars 2010
NOW DECIDE WHAT YOU
WANT TO KNOW
• WITH YOUR GROUP decide what
aspect of this photo you think will best
help you understand it.
Dr. C. Renee James NASA Top Stars 2010
And the nominees are…
• The piece of information that will help us
understand more about this picture is…
–
–
–
–
–
–
–
–
–
Why so many?
Why different colors?
How far from us? Distance norms?
Why brighter/dimmer?
Why clustered in the middle/dispersed outside?
Why appear different sizes?
Can you tell temps?
How far from each other?
How old?
Dr. C. Renee James NASA Top Stars 2010
MY SECRET WEAPON
• I don’t tell the students this, but there are
typically only two basic things they will
ever want to explore: Distances (or
anything spatial about the picture) or light
(anything relating to the colors or
brightness). I prepare the two “lectures”
ahead of time, but it’s up to them which one
they begin with.
• Then I hold a vote. This semester they
chose…
Dr. C. Renee James NASA Top Stars 2010
WHICH ONE??
1.Light
2. Distances
Dr. C. Renee James NASA Top Stars 2010
At this point, they think they’ve
probably seen the last of NGC 6397.
• Boy are THEY wrong! BWAHAHAHAA!
• To be honest, though, I had no idea that this
image would get so enmeshed in my entire
semester.
• For the classes that begin exploring light,
we play with light bulbs on dimmer
switches and get some info about
color/temperature/brightness relationships.
• Once that’s done, I ask the following:
Dr. C. Renee James NASA Top Stars 2010
Two stars are exactly the same size and distance
from us. One appears orange. The other appears
white. ASSUMING THAT STARS BEHAVE
LIKE LIGHT BULBS, which one do you THINK
will appear brighter?
1.
2.
3.
4.
The orange one
The white one
They’ll both be the same brightness
Need more information
Dr. C. Renee James NASA Top Stars 2010
Voting Questions
• The previous slide is an example of a ‘voting
question’ that I present often in class.
• Students simply hold the number of fingers to
their chest to indicate their answer.
• If the vote is mostly correct, we can move on.
If not, well…looks like I need to explain
things better.
• Then I hit them with this:
Dr. C. Renee James NASA Top Stars 2010
Do THESE
behave the way
you expect if stars
act like light
bulbs?
If not, what is
different from
what you expect?
Dr. C. Renee James NASA Top Stars 2010
Thank you, NGC 6397
• One of the more obvious features in this
Hubble photo is that the orange stars tend to
appear brighter. And yet my students have
found that for light bulbs, white is brighter
than orange.
• This leads to possible solutions:
– Orange stars in that photo are closer
– Orange stars in that photo are bigger
– Stars don’t behave like light bulbs
Dr. C. Renee James NASA Top Stars 2010
SEVERAL CLASSES LATER…
• Students are convinced that stars do in fact
get their colors from their temperatures and
not from their composition (e.g. discharge
tubes like neon or helium lights), leaving
only the size and distance issues.
• We explore size first with an group exercise
from Prather, et al’s Lecture Tutorials for
Intruductory Astronomy.
• Then we see the cluster again…
Dr. C. Renee James NASA Top Stars 2010
Orange stars – like
orange light bulbs – are
cool.
>So each square inch
of an orange star is
DIMMER than each
square inch of a white
star.
>But there are zillions
more square inches in
these orange stars (not
a general rule about
orange stars)
Dr. C. Renee James NASA Top Stars 2010
If you’re keeping score at
home…
• We’ve now looked at the image of NGC
6397 three times in class, and we’re only a
few days into the semester.
• Students are suggesting that we give it a
new name like “Bob.”
• Might not be a bad idea because, after all…
Dr. C. Renee James NASA Top Stars 2010
Her name is Polly
Puffball. I can keep
her…Right, Mom?
…naming things gives them a special place in your
heart.
But…is it possible that NGC 6397 would ever hold a
special place in their hearts? Hmmm…
Dr. C. Renee James NASA Top Stars 2010
Back to Bob…er, NGC 6397
• It IS still possible that the orange stars are
simply closer (although that’s a really
creepy proposition since they’d be ganging
up on us).
• So we spend some time going over stellar
distance determinations via parallax.
• Everyone’s happy with parallax because
you can personally observe “finger
parallax.”
Dr. C. Renee James NASA Top Stars 2010
Then the hammer
falls…
• At 8200 light years,
Bob is too far away
for our current
technology to detect
stellar parallax.
• But somehow we
KNOW how far away
it is.
• Is Bob lying to us??
Dr. C. Renee James NASA Top Stars 2010
This opens another door
• Parallaxes and colors are just the first step.
• Now we can explore stellar spectra,
including spectral types and luminosity
classes, always hearkening back to Bob.
• Spectroscopic parallax can be applied to
this cluster, yielding a distance.
• In addition, we can explore Bob’s HR
Diagram.
Dr. C. Renee James NASA Top Stars 2010
So many
awesome
features to
figure out!
From “The CM diagram of the nearby globular cluster NGC 6397” 1987. AJ, vol 94. Authors:
Alcaino, G.; Buonanno, R.; Caloi, V.; Castellani, V.; Corsi, C. E.; Iannicola, G.; Liller, W.
Dr. C. Renee James NASA Top Stars 2010
Questions from the students include…
• What the heck is B-V?
• Why isn’t this a pretty HR Diagram like the
ones in the book?
• Why does the main sequence just quit
halfway up?
• Why is there a “wishbone” shape in the upper
right?
• What are the stars that look like they’re in the
main sequence, but hotter?
Dr. C. Renee James NASA Top Stars 2010
Clearly Bob is thwarting their
attempts to understand stars
• Fortunately, we can then go into stellar
masses, stellar evolution, main sequence
turnoffs, and how to determine cluster ages
(pretty standard for intro astronomy course)
• But we ALSO can go into blue stragglers,
age determination from white dwarfs
(which are plentiful in Bob), and a host of
other more “cutting edge” topics that arise
from studying this cluster.
Dr. C. Renee James NASA Top Stars 2010
Assessing the Value of Bob
• It’s all well and good to say Bob has
dominated the semester, but how does this
get assessed?
– Informally via voting questions and group
work, such as listing what can be determined
about Bob.
– Formally via homework and exam questions.
• Here are some examples (in slide form):
Dr. C. Renee James NASA Top Stars 2010
The next slide is a group
discussion question
Dr. C. Renee James NASA Top Stars 2010
BACK TO THAT FIRST PICTURE…
• ALL of the stars in
this photo have
essentially the same
PARALLAX.
• WHAT DOES THIS
TELL YOU ABOUT
THE ACTUAL
BRIGHTNESS OF
THESE OBJECTS?
• What do you think
this means about
their relative SIZES?
Dr. C. Renee James NASA Top Stars 2010
The next two slides are sample
voting questions from class
Dr. C. Renee James NASA Top Stars 2010
Bob has a distance of 8200 light
years. Approximately what is the
parallax to one of its stars?
1.
2.
3.
4.
5.
1/8200 arcseconds
8200 arcseconds
1/2700 arcseconds
2700 arcseconds
Need more info
Dr. C. Renee James NASA Top Stars 2010
If Bob’s orange stars
have an apparent
magnitude of 12.3,
what would be an
appropriate apparent
magnitude for the
white ones?
1)16
2)12.3
3) 9
Dr. C. Renee James NASA Top Stars 2010
Another discussion question,
followed quickly by a voting
question, and some more
discussion (Bob really takes over
this class day):
Dr. C. Renee James NASA Top Stars 2010
The HR
Diagram for
Bob
• In your groups,
list some features
that you can see in
this diagram.
Which ones are
unexpected?
• What do you want
to learn next?
Dr. C. Renee James NASA Top Stars 2010
From Bob’s HR-Diagram:
• No stars hotter than B-V of about 0.5 on
MS
• This is equivalent to spectral type F7, give
or take.
• Sun is G2V, and has a mass of 1.0 solar
masses (by definition).
Dr. C. Renee James NASA Top Stars 2010
What does this say about the masses of Bob’s
Main sequence stars?
1. There are no MS stars more massive than
about 1.4x the mass of the Sun
2. There are no MS stars less massive than about
1.4x the mass of the Sun the Sun
3. The MS stars in NGC 6397 have a wide range
of masses from much more to much less
massive than the Sun
Dr. C. Renee James NASA Top Stars 2010
• CAN YOU THINK OF ANY POSSIBLE
REASONS WHY THIS CLUSTER DOESN’T
HAVE ANY MAIN SEQUENCE STARS
GREATER THAN 1.4 SOLAR MASSES?
• DISCUSS…
• (Proposed solutions typically include possibility
that cluster is too YOUNG and high-mass stars
haven’t formed yet; too OLD and high-mass stars
have died; region of the galaxy was abnormal and
high-mass stars couldn’t form to begin with. Or a
giant space echidna ate them.)
Dr. C. Renee James NASA Top Stars 2010
And, after a couple of weeks of
stellar formation and evolution, a
couple more voting questions.
Dr. C. Renee James NASA Top Stars 2010
Why doesn’t Bob have any stars
greater than 1.4 solar masses on the
main sequence?
1. The cluster is too young to have pulled
enough material to form high-mass stars.
2. The higher mass stars are too dim to see.
3. The higher mass stars have already used up
their core hydrogen fuel and left the MS.
4. The higher mass stars broke apart into lowmass stars.
Dr. C. Renee James NASA Top Stars 2010
BOB
• MS ends around
B-V = +0.5
• This is about
spectral type F7.
• Sun is G2.
IS NGC6397
1) older than
2) younger than
10 billion years
old??
Dr. C. Renee James NASA Top Stars 2010
Then the
inevitable…
Dr. C. Renee James NASA Top Stars 2010
Here lies Bob.
But before we bid adieu to our
friend Bob (nee NGC 6397), let’s say
some kind words about it…
Dr. C. Renee James NASA Top Stars 2010
Goodbye, Bob. We’ll miss you. We
really enjoyed finding out about your…
• (and the students get together and list
EVERYTHING that they have learned about this
cluster from day one through this point in class,
which is about 9 or 10 weeks later. They are truly
astonished at how much of a stars and galaxies
class can be pulled together from just one cluster
and a simple question at the beginning of the
semester).
Dr. C. Renee James NASA Top Stars 2010
AND HERE’S WHAT
THEY LIST:
Luminosity
Temperature
Size
Magnitudes (absolute and
apparent)
Parallax and Spectroscopic
Parallax
Stellar Masses
Stellar Evolution
Age of the cluster
White dwarfs
Blue Stragglers
…and much, much more!
Dr. C. Renee James NASA Top Stars 2010
Good ol’ Bob…
• Virtually half of a college-level introductory
astronomy class for non-majors derives
from a single photo from the Hubble
Heritage.
• Bob turns out to be quite the conceptual
anchor (and not so much of a ‘bob.’)
Dr. C. Renee James NASA Top Stars 2010
REFERENCES
• How to locate Bob:
http://heritage.stsci.edu/2003/21/index.html
• And his HR Diagram:
“The CM diagram of the nearby globular cluster
NGC 6397” 1987. AJ, vol 94. By
Alcaino, G.; Buonanno, R.; Caloi, V.;
Castellani, V.; Corsi, C. E.; Iannicola, G.;
Liller, W.
Dr. C. Renee James NASA Top Stars 2010
Educational Resources (in slightly larger font than before)
•
•
•
•
•
•
•
•
•
Abell, S., Martini, M., & George, M. 2001, 'That's What Scientists Have To Do': Preservice
Elementary Teachers' Conceptions of the Nature of Science During a Moon Investigation,
International Journal of Science Education, 23(11), 1095.
Adams, J. P., & Slater, T. F. 1998, Mysteries of the Sky: Activities for Collaborative Groups,
Dubuque, IA: Kendall Hunt Publishing, 1998a.
Adams, J. P., & Slater, T. F. 1998, Using Action Research To Bring the Large Lecture Course Down
to Size, Journal of College Science Teaching, 28, 87, 1998b.
Adams, J. P., & Slater, T. F. 2002, Learning Through Sharing: Supplementing the Astronomy
Lecture with Collaborative-Learning Group Activities, Journal of College Science Teaching, 31, 384.
Adams, J. P., Brissenden, G., Lindell, R. S., Slater, T. F., & Wallace, J. 2002, Observations of
Student Behavior in Collaborative Learning Groups, Astronomy Education Review, 1(1), 25.
http://aer.noao.edu/AERArticle.php?issue=1&section=1&article=2.
Adams, J. P., Prather, E. E., & Slater, T. F. 2002, Lecture-Tutorials for Introductory Astronomy,
Preliminary Ed., Upper Saddle River, NJ: Prentice Hall.
Albanese, A., Danhoni Neves, M. C., & Vicentini, M. 1997, Models in Science and in Education: A
Critical Review of Research on Students' Ideas About the Earth and Its Place in the Universe, Science
and Education, 6, 573.
American Association for the Advancement of Science Project 2061. 1993, Benchmarks for Science
Literacy, New York: Oxford University Press.
Ashcraft, P., & Courson, S. 2003, Effects of an Inquiry-Based Intervention to Modify Pre-Service
Teachers' Understanding of Seasons, Paper presented at the Annual Meeting of theNational
Association for Research in Science Teaching, March, Philadelphia, PA.
Dr. C. Renee James NASA Top Stars 2010
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•
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•
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Ball, N., Coyle, H. P., & Shapiro, I. I. (Eds.). 1994, Project SPICA: A Teacher Resource to Enhance
Astronomy Education, Dubuque, IA: Kendall-Hunt Publishing.
Bieniek, R. J., & Zeilik, M. 1976, Follow-up Study of a PSI Astronomy Course, American Journal of
Physics, 44(7), 695.
Bisard, W. J., Aron, R. H., Francek, M. A., & Nelson, B. D. 1994, Assessing Selected Physical
Science and Earth Science Misconceptions of Middle School Through University Preservice
Teachers: Breaking the Science 'Misconception Cycle', Journal of College Science Teaching, 24, 38.
Bishop, J. E. 1977, United States Astronomy Education: Past, Present, and Future, Science
Education, 61, 295.
Bobrowsky, M. 2000, Teaching Evolutionary Processes to Skeptical Students, The Physics Teacher,
38, 565.
Brissenden, G. 2001, SABER Astronomy Online Database: Searchable Annotated Bibliography of
Education Research, Retrieved February 15, 2002, from http://www.cdes-astro.com/saber/index.htm.
Casey, T. L., & Slater, T. F. 2002, A Comparison of Group and Individually Completed Course
Evaluations in Introductory Astronomy, Astronomy Education Review, 1(2), 1.
http://aer.noao.edu/AERArticle.php?issue=2&section=2&article=3.
Comins, N. F. 2000, A Method To Help Students Overcome Astronomy Misconceptions, The
Physics Teacher, 38, 542, 2000a.
Comins, N. F. 2000, An In-Your-Face Approach to Student Misconceptions About Astronomy,
Unpublished manuscript, 2000b.
Comins, N. F. 2001, Heavenly Errors: Misconceptions About the Real Nature of the Universe, New
York: Columbia University Press.
Dr. C. Renee James NASA Top Stars 2010
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Finegold, M., & Pundak, D. 1990, Students' Conceptual Frameworks in Astronomy, Australian
Science Teachers Journal, 36, 76.
Fraknoi, A. 1998, Astronomy Education: A Selective Bibliography, Retrieved April 6, 2003, from
http://www.astrosociety.org/education/resources/educ_bib.html.
Hemenway, M. K., Straits, W. J., Wilke, R. R., & Hufnagel, B. 2002, Educational Research in an
Introductory Astronomy Course, Innovative Higher Education, 26(4), 271.
Kikas, E. 1998, The Impact of Teaching on Students' Definitions and Explanations of Astronomical
Phenomena, Learning and Instruction, 8, 439.
Lightman, A., & Sadler, P. M. 1993, Teacher Predictions Versus Actual Student Gains, The Physics
Teacher, 31, 162.
Maran, S. P. 2000, 'Hot Topics' in Astrophysics, The Physics Teacher, 38, 550.
National Research Council. 1996, National Science Education Standards, Washington, D.C.:
National Academy Press.
National Research Council. 1999, How People Learn: Brain, Mind, Experience, and School,
Washington, D.C.: National Academy of Sciences.
Offerdahl, E. G., Prather, E. E., & Slater, T. F. 2002, Students’ Pre-Instructional Beliefs and
Reasoning Strategies About Astrobiology Concepts, Astronomy Education Review, 1(2), 5.
http://aer.noao.edu/AERArticle.php?issue=2&section=2&article=1.
Pasachoff, J. M. 2001, What Should Students Learn?, The Physics Teacher, 39, 381.
Dr. C. Renee James NASA Top Stars 2010
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•
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•
•
Pasachoff, J. M. 2002, Pasachoff's Points, The Physics Teacher, 40, 197, 2002a.
Pasachoff, J. M. 2002, What Should College Students Learn? Phases and Seasons? Is Less More or Is
Less Less?, Astronomy Education Review, 1(1), 124.
http://aer.noao.edu/AERArticle.php?issue=1&section=4&article=3, 2002b.
Schneps, M. P. 1989, A Private Universe, Video. San Francisco: Astronomical Society of the Pacific.
Shawl, S. J. 2000, 'It’s ONLY a Theory': What Do Students Know About the Scientific Enterprise?,
Poster session presented at the 195th Meeting of the American Astronomical Society, January,
Atlanta, GA.
Skala, C., Slater, T. F., & Adams, J. P. 2000, Qualitative Analysis of Collaborative Learning Groups
in Large Enrollment Introductory Astronomy, Publications of the Astronomical Society of Australia,
17, 185.
Skam, K. 1994, Determining Misconceptions About Astronomy, Australian Science Teachers
Journal, 40(3), 63.
Slater, T. F., & Adams, J. P. 2003, Learner-Centered Astronomy: Strategies for Teaching ASTRO
101, Upper Saddle River, NJ: Prentice Hall.
Slater, T. F., Adams, J. P., Brissenden, G., & Duncan, D. 2001, What Topics are Taught in
Introductory Astronomy Courses?, The Physics Teacher, 39, 52.
Slater, T. F., Carpenter, J. R., & Safko, J. L. 1996, Dynamics of a Constructivist Astronomy Course
for In-Service Teachers, Journal of Geoscience Education, 44, 523.
Slater, T. F., Prather, E. E., Bailey, J. M., & Adams, J. P. 2003, Effectiveness of a Lecture-Tutorial
Approach to Large Enrollment Introductory Astronomy, Paper presented at the Annual Meeting of
the National Association for Research in Science Teaching, March, Philadelphia, PA.
Dr. C. Renee James NASA Top Stars 2010
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•
•
•
•
Trumper, R. 2001, A Cross-College Age Study of Science and Nonscience Students' Conceptions of
Basic Astronomy Concepts in Preservice Training for High-School Teachers, Journal of Science
Education and Technology, 10(2), 189, 2001c.
Vosniadou, S., & Brewer, W. F. 1987, Theories of Knowledge Restructuring in Development,
Review of Educational Research, 57(1), 51.
Zeilik, M. 1981, Flexible, Mastery-Oriented Astrophysics Sequence, American Journal of Physics,
49(9), 827.
Zeilik, M. 1998, Interactive Lesson Guide for Astronomy, Revised Ed., Santa Fe, NM: The Learning
Zone.
Zeilik, M., Schau, C., Mattern, N., Hall, S., Teague, K. W., & Bisard, W. J. 1997, Conceptual
Astronomy: A Novel Model for Teaching Post-Secondary Science Courses, American Journal of
Physics, 65, 987.
I think that about does it….
Dr. C. Renee James NASA Top Stars 2010
APPENDIX
• The following slides are taken directly from
the first couple of days of the semester
(assuming they choose “light” as the
direction at the beginning of class)
• If you would like to see how NGC 6397
keeps cropping up in my classes, or if you
wish to see how I tackle a vote of
“distance,” feel free to contact me.
Dr. C. Renee James NASA Top Stars 2010
A jillion points of
light (stars)
What can you tell from just
this picture?
Are all stars the same?
What’s different?
WHAT SPECIFIC
INFORMATION DO YOU
THINK WOULD HELP
YOU UNDERSTAND
MORE ABOUT THESE
STARS?
Dr. C. Renee James NASA Top Stars 2010
First group assignment:
• Name five things that you can tell about
NGC 6397 JUST BY LOOKING AT THIS
PHOTO. Think small (very small) like a child.
Dr. C. Renee James NASA Top Stars 2010
Now for a more involved group
assignment:
• Several things might help you better understand that
picture. For instance, finding out what makes the stars
different colors could help, or perhaps if you knew how far
away these things are from Earth, or if you knew about the
actual sizes of these dots... There are tons of things that
could help you find out what’s really being shown in this
picture.
• WITH YOUR GROUP – come up with WHAT YOU
WANT TO KNOW ABOUT THIS PICTURE and what
that knowledge will help you understand. For example, “I
want to know how fast sound travels. That way I can tell
how far away a lightning strike is simply by counting the
seconds until the sound (thunder) gets to me.”
Dr. C. Renee James NASA Top Stars 2010
And the class vote is…
• The piece of information that will help us
understand more about this picture is…
– (students offer their answers)
Dr. C. Renee James NASA Top Stars 2010
WHICH ONE??
1.Light
2. Distances
Dr. C. Renee James NASA Top Stars 2010
IN YOUR EXPERIENCE
what causes things to appear
orange?
• (again, students offer their own observations, but
here’s what I got last semester)
• Paint, orange – reflecting stuff.
– YOU’LL HAVE TO TAKE MY WORD FOR
NOW THAT THE STARS ARE NOT
REFLECTING LIGHT LIKE MARS DOES.
They make their own.
• Fire, neon sign, stove burner, glow in the dark
thingies – stuff that makes its OWN light.
vDr. C. Renee James NASA Top Stars 2010
So what kind of info can we get
from things giving off their own
light? Let’s start simple…
• An incandescent (filament) light bulb on dimmer
switch.
• Turn it low. Look at it. Put your hand near it.
What does it look like (color, brightness)? How
hot does it feel (warmish, hot, very hot)?
• Turn it medium.
• Turn it high.
• What conclusions can you draw about objects that
behave like LIGHT BULBS?
Dr. C. Renee James NASA Top Stars 2010
RESULTS
COLOR
BRIGHTNESS TEMP
LOW
Orange
Dim
MED
Whitish
Kinda brighter
orangeish
yellowish
beige salmony
color.
White
Blinding
HIGH
Dr. C. Renee James NASA Top Stars 2010
Lukewarm
Warm to hot
Really hot
Two stars are exactly the same size and distance
from us. One appears orange. The other appears
white. ASSUMING THAT STARS BEHAVE
LIKE LIGHT BULBS, which one do you THINK
will appear brighter?
1.
2.
3.
4.
The orange one
The white one
They’ll both be the same brightness
Need more information
Dr. C. Renee James NASA Top Stars 2010
Do THESE
behave the way
you expect if stars
act like light
bulbs?
If not, what is
different from
what you expect?
Dr. C. Renee James NASA Top Stars 2010
COLOR = TEMPERATURE?
• From light bulbs, we see a nice correlation
between color and temperature (white =
OW!; yellow = hot; orange = coolish)
• Temperature also affects BRIGHTNESS.
• But the orange stars in the photo tend to be
BRIGHT, rather than dim; the white stars
tend to be DIM, rather than bright.
– So maybe stars DON’T behave like light bulbs.

Dr. C. Renee James NASA Top Stars 2010
Let’s look at a different type of light
source:
• “Discharge” tubes (hydrogen, mercury, helium).
• Different composition tubes appear different colors.
• What does spectrum (as seen through the diffraction
grating) look like?
• What does a normal LIGHT BULB look like through
diffraction grating? [all students have a diffraction
grating passed out to them at the beginning of class]
Dr. C. Renee James NASA Top Stars 2010
2 Mechanisms to Produce Light
• One relates to TEMPERATURE (e.g. light bulb)
and gives continuous spectrum:
• Other relates to COMPOSITION (e.g. discharge
tubes) and gives emission spectrum:
• So which one is responsible for the different
colors of stars?
Dr. C. Renee James NASA Top Stars 2010
Do stars display a spectrum more
like the emission spectrum or more
like a light bulb’s spectrum?
• You’ve probably all seen at least one star’s
spectrum in your lives.
• Which star? What does its spectrum look
like? [they’ll usually get it after a tiny bit of
prompting]
Dr. C. Renee James NASA Top Stars 2010
STELLAR SPECTRUM =
RAINBOW!
• Sun gives one off.
• Stars do, too.
(to a first approximation,
at least, but all those
dark lines have to wait
for another class)
Dr. C. Renee James NASA Top Stars 2010
Now it’s time for a fleet of voting
questions. Personal response
devices ready???? [in my classes,
the students use their hands to
indicate their answers]
Dr. C. Renee James NASA Top Stars 2010
A light bulb's color is a result of its...
1. composition
2. temperature
A discharge tube (e.g. those long glass tubes I
plugged into that big power supply) gets its color
from its... (Same choices as above)
Dr. C. Renee James NASA Top Stars 2010
A light bulb's spectrum looks like ____, while
a discharge tube's spectrum looks like ___.
1. a rainbow; a rainbow
2. a series of different colored lines; a
series of different colored lines
3. a rainbow; a series of different colored
lines
4. a series of different colored lines; a
rainbow
Dr. C. Renee James NASA Top Stars 2010
A STAR'S spectrum (think of the Sun) looks
like...
1. a rainbow
2. a series of different
colored lines
THEREFORE a star's light must be produced
the same way a _____'s light is produced.
1. light bulb
2. discharge tube
Dr. C. Renee James NASA Top Stars 2010
AND THIS MEANS a star's color is related to
its...
1. temperature
2. composition
Dr. C. Renee James NASA Top Stars 2010
WHAT HAVE WE FOUND
OUT SO FAR?
• We’ve demonstrated that the Sun and stars
produce light the same way that a LIGHT
BULB does.
• (but we haven’t shown that the sun is a star.
We also haven’t shown that the Sun is a
light bulb)
• Thus their COLORS must be related to their
TEMPERATURES, not their compositions.
• But then we still have a problem…
Dr. C. Renee James NASA Top Stars 2010
SO HOW CAN THE ORANGE
STARS BE THE BRIGHT
ONES???
• Lower temp light bulb = orange, but dim.
• Higher temp light bulb = white, but bright.
• In NGC 6397, orange stars are the bright
ones, not the dim ones.
• ??????? ANY IDEAS????? [again, class
discussion ensues]
Dr. C. Renee James NASA Top Stars 2010
• Now it’s time to get into the Lecture Tutorials.
Please get with a couple of people and work your
way through questions 1-9 pp 53-55. Take this
and all LT exercises pretty seriously – it’ll all
come back to haunt you. (BWAHAHAHAHA!!)
• Dr. Miller has made a series of videos to help
illustrate astronomical concepts:
http://video.google.com/videoplay?docid=669073
0625344739278&ei=YKy-SKuMH4zqAGyl_31CQ&q=%22astronomy+001%22
Dr. C. Renee James NASA Top Stars 2010
LUMINOSITY
• Fancy term for how much energy a star is
pumping out each second.
• Does NOT depend on distance (it’s the
WATTAGE. A 100-W light bulb is still
100-W light bulb even if it’s in Chicago)
• TWO THINGS INFLUENCE
LUMINOSITY. You can make a star
MORE LUMINOUS by doing what?
Dr. C. Renee James NASA Top Stars 2010
Still assuming that stars behave like
light bulbs, how can an orange star
APPEAR brighter than a white star?
1.
2.
3.
4.
The orange star is more distant
The orange star is larger
The orange star is hotter
There is no mystery here – from what we
know of light bulbs, orange stars
SHOULD be brighter than white stars.
Dr. C. Renee James NASA Top Stars 2010
Orange stars – like
orange light bulbs – are
cool.
>So each square inch
of an orange star is
DIMMER than each
square inch of a white
star.
>But there are zillions
more square inches in
these orange stars (not
a general rule about
orange stars)
Dr. C. Renee James NASA Top Stars 2010
How big are
they?
The harsh
reality:
The Sun
compared to
a red giant
Dr. C. Renee James NASA Top Stars 2010
CONCLUSIONS
• Light bulbs, the Sun, and stars give off continuous
spectra (i.e. rainbows)
– Colors of these objects arise from differences in
temperature, not composition.
– This is not yet conclusive evidence that the Sun is a star,
though!
• Can make light bulbs – or STARS – brighter by
increasing temp OR size.
– Orange stars in the photo in question are cool, but
HUGE! (they’re red giants, in fact)
Dr. C. Renee James NASA Top Stars 2010