20180517

Astronomy final exam question: comparing temperatures and sizes of main-sequence stars

Astronomy 210 Final Exam, spring semester 2018
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:
Srr: Is it possible for two main-sequence stars to have different temperatures and different sizes but the same luminosity?
Rgr: No, because more massive main-sequence stars are hotter and larger than the lesser massive main-sequence stars, they cannot have the same luminosity.
Discuss why this answer is correct for main-sequence stars, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

[*] answers.yahoo.com/question/index?qid=20110511035317AAeHphE.

Solution and grading rubric:
  • p:
    Correct. Discusses how the Stefan-Boltzmann law and/or H-R diagram shows that along the main-sequence, the more-massive stars will be located in the hotter, larger, brighter upper left-hand corner, while the less-massive stars will be located in the cooler, smaller, dimmer lower right-hand corner, so they cannot have the same luminosity.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May have compared two stars in general, rather than explicitly comparing two stars on the main-sequence line.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30676
Exam code: finalSuB1
p: 24 students
r: 7 students
t: 4 students
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 0707):

Another sample "p" response (from student 0219):

Astronomy final exam question: comparing temperatures and luminosities of main-sequence stars

Astronomy 210 Final Exam, spring semester 2018
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:
NiH: Can a large size main-sequence star have a hotter temperature and brighter luminosity than a smaller size main-sequence star?
Bes: Yes, it could be possible that a large size main-sequence star can have a hotter temperature and brighter luminosity in comparison to a smaller size main-sequence star that has a cooler temperature and dimmer luminosity.
Discuss why this answer is correct for main-sequence stars, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

[*] answers.yahoo.com/question/index?qid=20101127053013AACmzKM.

Solution and grading rubric:
  • p:
    Correct. Discusses how the Stefan-Boltzmann law and/or H-R diagram shows that along the main-sequence, the larger stars will be located in the hotter, brighter upper left-hand corner, while the smaller stars will be located in the cooler, dimmer lower right-hand corner.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May have compared two stars in general, rather than explicitly comparing two stars on the main-sequence line.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30674
Exam code: finaln3sT
p: 9 students
r: 9 students
t: 1 student
v: 0 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 2123):

Astronomy final exam question: type II supernovae in star cluster with white dwarfs?

Astronomy 210 Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:
Pdg: Can there be type II supernovae explosions seen in a star cluster that also has white dwarfs at the same time? Would it have to be a really old or young star cluster?
spota: Yes, if the star cluster is old enough to contain white dwarf stars it will still be young enough to have hydrogen-burning massive stars that can undergo type II supernova explosions.
Discuss why this answer is incorrect, and how you know this. Explain using the properties of mass and stellar lifetimes, evolution of stars, and star cluster ages.

[*] answers.yahoo.com/question/index?qid=20171117015031AAqCPQo.

Solution and grading rubric:
  • p:
    Correct. Understands that star cluster cannot have type II supernovae explosions at the same time as having white dwarfs:
    1. medium-mass stars become white dwarfs well after the end of their main-sequence lifetimes (approximately 10 billion years); and
    2. massive stars will explode as type II supernovae after the end of their main-sequence lifetimes (less than a million years); such that
    3. a star cluster with white dwarfs, will not have any supergiants remaining that can explode as type II supernovae; or a star cluster with supergiants exploding as type II supernovae will have medium-mass stars that have not yet reached the end of their main-sequence lifetimes.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled discussion of properties and evolution of stars. May discuss type Ia supernovae or lookback time.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30674
Exam code: finaln3sT
p: 6 students
r: 3 students
t: 5 students
v: 4 students
x: 1 student
y: 0 students
z: 1 student

Section 30676
Exam code: finalSuB1
p: 13 students
r: 6 students
t: 6 students
v: 6 students
x: 3 student
y: 1 student
z: 1 student

A sample "p" response (from student 1777):

A sample "p" response (from student 1217), discussing the house party model of determining star cluster ages:

A sample "y" response (from student 7237):

Astronomy final exam question: metals breaking down in stars?

Astronomy 210 Final Exam, spring semester 2018
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:
Alexis: Why are metals more abundant in newer stars than older stars?
tdloo: Because the metals haven't had time to break apart yet in newer stars.
Discuss why this answer is incorrect, and how you know this. Explain using the properties of mass and stellar lifetimes, and evolution of stars.

[*] answers.yahoo.com/question/index?qid=20130409190107AA1Ej3v.

Solution and grading rubric:
  • p:
    Correct. Discusses why the answer is incorrect by discussing at least one of the following arguments:
    1. metals are produced in the cores of massive stars (and medium-mass supergiants) by fusion, which entails the combination of atoms, rather than in breaking them apart; or that
    2. metals are typically produced in the cores of previous generation ("old") massive stars, which explode as type II supernovae to scatter these metals that get incorporated into the next generation of "new" stars, such that metals are more abundant in newer stars than older stars.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled discussion of properties and evolution of stars, such as breaking down of metals; masses and evolution rates.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30674
Exam code: finaln3sT
p: 16 students
r: 0 students
t: 1 student
v: 1 student
x: 1 student
y: 0 students
z: 1 student

Section 30676
Exam code: finalSuB1
p: 19 students
r: 1 student
t: 2 students
v: 12 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 5069):

20180516

Online reading assignment question: advice to future students

Astronomy 210, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. The following question was asked after the last lecture, but prior to the final exam.

Tell a student who is about to take this course next semester what he/she needs to know or to do in order to succeed in this course. (Graded for completion.)
"Do your readings and show up everyday to class because it helps so much more than thinking you can just read the book and be good."

"Show up to class and study for every quiz, it takes a lot of the stress out of the class and makes it very enjoyable."

"Be curious and ask questions."

"Don't forget that the quizzes are due before each class at midnight! And if you're taking astronomy lab, too, it's easy to forget about those assignments as well."

"Make sure you use the starwheel the right way, read the chapters, study your notes and do EVERY online reading asssignment."

"ASK QUESTIONS AND PUT IN EFFORT! This class is so engaging. You'll learn so much. Do your homework, and come to class. It is all worth it. If you put the effort in you will pass this class easily. P-dog is the best."

"Study StUdY STUDY! Get a group of people from your class and study for all quizzes/exams/midterms, anything! It will help you out a lot and don't slack off."

"Always do the homework assignments, they are super-easy and pay attention in class. This is a great course and you will have a lot of fun."

"In order to succeed in this course you need to do the readings, and the homework is important and reviewing the presentations."

"DO THE READING ASSIGNMENTS. ATTEND EVERY LECTURE. BE AMAZED BY SPACE."

"In order to succeed in this class I urge everyone to look at the quiz study guides and make sure to do the online reading assignments."

"Don't procrastinate, go to class, and do the readings! They help immensely with following along in class."

"In order to succeed, I would recommend that you go to all the class sessions, do not forget a single online reading assignment, do all of the extra credit, and try your best not to procrastinate!"

"Preview then presentation slides online so you can be the more confident while being in class or with in-class activities."

"Read the chapter before class and keep your quizzes."

"If one is going to be enrolled in astronomy with Dr. Len, the most important thing to know in order to succeed is to follow @Patrick_M_Len on Twitter. He also posts everything on blogs, from former test questions with correct answers, along with the reading assignments and basically everything related to the course. And being aware of the blogs and what is posted there might help. Former midterm questions are good study guides and Dr. Len shows examples of students answers and grading rubric really shows how he grades and what he looks for."

"Please please PLEASE do the reading assignments and come to class."

"They need to be able to show up to class to get the points that are handed out. It really isn't that hard yet to just do the work that is asked of you."

"Study and listen during lectures."

"Do the homework."

"Read, read, read, and study...by reading."

"Don't get behind on the reading and ask a lot of questions."

"Keep up with reading, get as many points as possible."

"Come to class, do your reading, study for quizzes!"

"Take lots and lots of notes and seriously read the book. Plus make sure you draw the drawings P-dog does in class, they help."

20180509

Astronomy quiz question: spiral arm composition

Astronomy 210 Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA

The spiral arms of a galaxy are primarily composed of:
(A) dark matter.
(B) massive stars.
(C) globular clusters.
(D) type Ia and type II supernovae.

Correct answer (highlight to unhide): (B)

Massive main-sequence stars, which are the brightest and shortest-lived stars, form and die within a short time, essentially traveling the width of a spiral arm. Dark matter and globular clusters are mainly found in the halo of a galaxy, above and below the disk.

Section 30674
Exam code: quiz07nen4
(A) : 2 students
(B) : 8 students
(C) : 9 students
(D) : 2 students (No responses: 1 student)

Success level: 41% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.86

Section 30676
Exam code: quiz07SumM
(A) : 3 students
(B) : 16 students
(C) : 17 students
(D) : 2 students

Success level: 46% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.48

Astronomy quiz question: red dwarf metallicity

Astronomy 210 Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA

The amount of metals in the outer layers of metal-poor red dwarf will __________ over time.
(A) increase.
(B) remain constant.
(C) decrease.
(D) (A red dwarf cannot be metal-poor.)

Correct answer (highlight to unhide): (B)

Medium-mass and massive stars produce metals (elements heavier than hydrogen and helium) in their cores during their giant/supergiant phases, up through type Ia/II supernovae explosions. Along with their unused hydrogen, these metals are then scattered into the interstellar medium, which are then incorporated into later generations of stars. However, a red dwarf (low-mass star) will only be able to fuse hydrogen to helium, and does not produce more metals.

Section 30674
Exam code: quiz07nen4
(A) : 8 students
(B) : 10 students
(C) : 3 students
(D) : 1 student

Success level: 49% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.38

Section 30676
Exam code: quiz07SumM
(A) : 14 students
(B) : 9 students
(C) : 12 students
(D) : 3 students

Success level: 27% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

Astronomy quiz archive: Milky Way, nucleosynthesis, cosmology

Astronomy 210 Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz07nen4


Section 30674
0- 8.0 :  
8.5-16.0 :   ******** [low = 9.5]
16.5-24.0 :   **** [mean = 22.5 +/- 9.1]
24.5-32.0 :   *******
32.5-40.0 :   *** [high = 40.0]


Section 30676, version 1
Exam code: quiz07SumM


Section 30676
0- 8.0 :   ** [low = 7.5]
8.5-16.0 :   ***********
16.5-24.0 :   ************ [mean = 21.5 +/- 8.0]
24.5-32.0 :   ********
32.5-40.0 :   ***** [high = 40.0]

Online reading assignment: origin of life, are we alone? (SLO campus)

Astronomy 210, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on the origin of life, a "Here Is Today" timeline, LEGO® washing tips and the extraterrestrial hypothesis.

Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"The age of this world; I think that it's interesting Earth has been through many stages."

"That chemical evolution is not considered being alive even though it should be. It is creating something or changing something which makes it seem alive."

"Your pictures are cool because it helps me to visualize what we are learning about and I like that."

"The timeline of Earth, and when life starting appearing, because it is really mind-blowing to see it on a timeline."

"Learning about carbon molecule chains was really interesting. The fact that all the information needed to survive and reproduce is stored on those simple chains is sort of mind-boggling."

"Possible life on other planets because I believe it's kinda scary."

"Origin of life on Earth. Its interesting because it has brought much debate from the science and religious societies."

"The definition of life is interesting. Thinking about life in the way that it does versus what it is."

"I find the history of life on Earth very interesting and the fact that we are such a small part of our history as a planet, yet we will probably be the ones to destroy it, very sad."

"I'm super-interested in the idea of intelligent life throughout our universe, such as traveling between the stars, it's crazy that the fastest human device launched will take about 90,000 years to travel to the nearest star."

"There is an equation for finding the number of communicative civilizations in our galaxy."

"I really enjoyed learning about the Drake equation because though there is no way of using it currently, it is interesting to hear that there is an active search of other advanced life and that it is thought of as a serious possibility."

"I definitely thought that the Drake equation was very interesting. I did not know that it was possible to even form such an equation, yet here it is! I love it."

"I've always found extraterrestrial life interesting and think that it would completely change our lives and culture if we actually were able to converse or communicate with what's out there."

"That this is our last lecture."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I don't understand the timeline you inserted. Like why? What does it mean?"

"I didn't really understand the process in which Julia Child went through to describe the how life on Earth begun."

"I am so CONFUSED of how we haven't been around for that long."

"Traveling between stars because of how long it seems to take to get to each one."

"Carbon molecule chains. 'In order to do things that livings things do, and more importantly, to make sure that a future generation is able to continue doing these things requires a lot of instructions to be stored.' MIND BLOWN."

"I was confused on the chemical evolution portion of this assignment. I thought it was really hard to grasp the idea of things naturally joining together in the fact of adapting to certain area's around Earth. Thus, evolution."

"How the chemistry works with molecules, this is confusing because I need it to be explained since for me chemistry is hard."

"The Drake equation was really confusing for me. I don't know how exactly all those variables are expressed or how they constrain the probability of life in a real sense."

"As usual, the thing I find the most interesting is the same thing that confuses me the most. I do not know what makes up the Drake equation, or how someone even came up with it."

"Everything confused me."

"Nothing really."

Briefly describe a difference between life and non-living things.
"Living things breathe and can reproduce, while non-living things cannot."

"Living things are organisms that are made up of atoms and cells that allow life to move and talk and feel. Inanimate and non-living objects cannot do this."

"A living thing has to be able to adapt in the environment but dose not have to if it is non-living."

"Living things can adapt themselves and their surroundings to accommodate survival, non-living things may last for centuries, but could eventually fade away."

"Life is the ability for cells to grow, develop, manipulate its environment, and have future generations while non-living things have no live cells."

"Living things can evolve and adapt whereas non-living things cannot. One way to tell whether or not something is non-living is to play the song 'Hey Ya!' by OutKast. If the thing does not dance or sing along to the song, it is non-living."

"Living things are alive, non-living things are not."

Rank the time it takes for each of the following to have occurred on Earth.
(Only correct responses shown.)
Time after the formation of Earth for single-cell life to arise: about 1 billion years [13%]
Time for the first types of simple single-cell life to evolve into fishlike creatures: about 3 billion years [4%]
Time for fishlike creatures to evolve into more complex land-based animals today: about 0.5 billion years [38%]

How important is it to you to know whether or not there may be life elsewhere other than on Earth?
Unimportant.  * [1]
Of little importance.  **** [4]
Somewhat important.  **** [4]
Important.  ****** [6]
Very important.  ********* [9]

Briefly explain your answer regarding the importance of knowing whether there may be life elsewhere other than on Earth.
"I feel like Earth is the only place where people can actually survive. It would interesting to know what new discoveries scientists would make but it's not like it would benefit me in anyway. You know what I mean."

"I just want to verify that there are other living organisms in the universe, even if this is as simple as a single-celled organism. Only because that organism can evolve just like we did."

"Because it'd be cool to know of other life forms and see how they live and see if their lifestyle is better than ours."

"Life elsewhere scares me. You don't know if they're gonna be friendly or not."

"I think that there's no way that we are the only living things in this universe, or anywhere other than Earth. It's interesting to think about what it may be, it's (probably) not little green aliens in a flying saucer, but who knows?"

"I think it is important because I don't think that we are alone. Knowing if there is life on other planets could help us answer a lot of questions that we have about our galaxy and may help us with things we are trying to research and fix."

"Other life forms could possibly inform us about how our universe was created, or how life itself has turned into what we know today. finding other organisms would be a huge development in human existence."

"Knowing that there is life elsewhere doesn't change my daily life here."

"I struggled between selecting 'somewhat important' and 'important.' I think that life elsewhere could potentially help but I'm not sure to what extent."

"We are wired for discovery and the fascination of being able to prove life elsewhere is something humans will strive to learn."

"My own personal reason would be existence and the meaning of it. I sometimes go down the rabbit hole of intense thought surrounding this. If we found out that there was life elsewhere I believe it would provide some comfort to me knowing that we aren't in this alone. Not necessarily that there's a purpose to all this but it might create more meaning to our own existence."

"There is no way that we are the only living beings in the universe. I want to know what else is out there."

"It would be very important to know if there was life on other planets or further in the universe. This mostly is because of the natural feeling we get as humans wanting to know more and more in life and where people and living being exist at."

"I love aliens, I love X-Files, and everyone needs to know that life beyond Earth life is important and cool and amazing. The truth is out there."

Which type of star would be least likely to have a planet that could support life?
Although not totally unimportant, right now it does not affect the way I live.
Massive.  ******** [8]
Medium-mass.  ****** [6]
Low-mass (red dwarf).  ***** [5]
(Unsure/guessing/lost/help!)  ****** [6]

Briefly explain your answer to the previous question (type of star least likely to have a planet that could support life).
"Massive stars, because they have a very short life span so they wouldn't be very likely for life to exist on a planet around them."

"It would take about a billion years or so for life to develop elsewhere and massive star wouldn't live that long."

"Because a massive star dies too quickly."

"Massive stars would have the lowest chance of hosting life because they would offer the shortest window of time for life to form because of its shorter main sequence lifetime."

"A low mass star would more than likely not be able to generate enough heat to create life on a terrestrial planet."

"Medium-mass stars would most likely have a planet with complex lifeforms because they wouldn't die as quickly as massive stars, and not be as dim as low-mass stars."

"I don't think any of the stars would have life."

"Wouldn't all of them be unable to have complex forms of life? Since that would be my answer, and it is not even an option, I am wrong and confused lol."

"I guessed."

Describe what the Drake equation is used for.
"A serious look at the possibility of life elsewhere in the Milky Way."

"It is a equation used to figure out now many extraterrestrial intelligent civilizations are out there that we can communicate with in the Milky Way."

"I have no idea."

In your opinion, how plausible is it that the Chilbolton message is a reply from extraterrestrials?
Implausible.  *** [3]
Not very plausible.  ************ [12]
Somewhat plausible.  ****** [6]
Very plausible.  * [1]
(Unsure/guessing/lost/help!)  ** [2]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Do you believe in extraterrestrial life?" (Eh, maybe. We won't really know unless we keeping looking, though.)

"How long do you think it will take most people to do the final exam? (About the same amount of time as a midterm, anywhere from 15-80 minutes, although you are allotted 120 minutes to take the final.)

"Do you think it's plausible that the Chilbolton message is a reply?" (Yes, it's a reply from the radio astronomers who work next door to that field. #mischiefmanaged)

"I'm really enjoying this class." (Now that it's nearly over?)

Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz07N4ci



Sections 30882, 30883 results
0- 6 :   ***** [low = 3]
7-12 :   ******
13-18 :   ******** [mean = 16.2 +/- 7.7]
19-24 :   ********
25-30 :   **** [high = 30]