20160503

Astronomy midterm question: IAU classification of centaurs

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

In our solar system, "centaurs" are objects that:
...circulate between Jupiter and Neptune on unstable orbits that cross the paths of one of the jovian planets. That means they're probably doomed, within ten million years or so, to be flung into the inner solar system or out into interstellar space... There's a lot that's not known about centaurs, including how many have enough gravity to pull themselves into a round shape, which would earn them the title of "dwarf planet."[*]
Discuss how centaurs that are not dwarf planets should be classified. Explain using the International Astronomical Union classification scheme.

[*] Marcus Woo, "First Asteroid With Rings Discovered" (March 26, 2014), on.natgeo.com/1h3G1oI.

Solution and grading rubric:
  • p:
    Correct. Of the three IAU requirements (orbits the sun directly, has a rounded shape, cleared/dominates its orbit), a dwarf planet satisfies the first two. A centaur that is not able to be a dwarf planet would then not be rounded in shape, but still share an orbit around the sun with the jovian planets, classifying it as solar system debris.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Understands how IAU requirements apply in correctly categorizing centaurs that aren't dwarf planets must be solar system debris, but discussion of requirements is not explicit, or only implied.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Explicitly lists IAU requirements, but does not apply them correctly/consistently.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion only tangentially related to the IAU classification scheme.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the IAU classification scheme.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30674
Exam code: midterm02n4s5
p: 10 students
r: 3 students
t: 7 students
v: 2 students
x: 0 students
y: 0 students
z: 0 students

Section 30676
Exam code: midterm02sLoX
p: 28 students
r: 6 students
t: 18 students
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1597) using the IAU classification flowchart:

Astronomy midterm question: same luminosity, but different temperature and size stars

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:
??: If two stars have the same luminosity, is it always true that the star with the lower temperature must be bigger?
qcp: Yes, that's true. A cooler star means that it must be bigger to be of equal 
luminosity.
Discuss why this answer is correct, 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=20160402221522AAZkrDm.

Solution and grading rubric:
  • p:
    Correct. Uses Wien's law, the Stefan-Boltzmann law and/or interprets H-R diagram to demonstrate how a cooler star must be bigger than a hotter star to have the same luminosity.
  • 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. 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: midterm02n4s5
p: 12 students
r: 3 students
t: 3 students
v: 1 student
x: 2 students
y: 1 student
z: 0 students

A sample "p" response (from student 1503), using both the "box method" to fill in relative Stefan-Boltzmann law parameters, along with using the diagonal lines on an H-R diagram to compare size:

A sample "x" response (from student 1096), appealing to recent tragic events in pop culture:

Astronomy midterm question: red dwarf same size as white dwarf?

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:
??: Can a red dwarf have the same size as a white dwarf?
Bpt: They can have the same size if the red dwarf was dimmer than the white dwarf.
Discuss why this answer is correct, 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=20160402083607AA27vRN.

Solution and grading rubric:
  • p:
    Correct. Uses Wien's law, the Stefan-Boltzmann law and/or interprets H-R diagram to demonstrate how a red dwarf can be the same size as a white dwarf by recognizing that:
    1. from Wien's law, the red dwarf is cooler than the white dwarf;
    2. from the Stefan-Boltzmann law (or interpreting an H-R diagram), the lower temperature red dwarf must have a lower luminosity than a white dwarf of the same size.
  • 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. 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: midterm02sLoX
p: 37 students
r: 8 students
t: 4 students
v: 3 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 0796), using the "box method" to fill in relative Stefan-Boltzmann law parameters:

A sample "p" response (from student 5713), using the diagonal lines on an H-R diagram to compare size:

A sample "p" response (from student 8041):

Astronomy midterm question: star cluster with white dwarfs?

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

Discuss which H-R diagram is more likely to be a star cluster with type II supernovae (which are deliberately not shown). Explain using the properties of mass and stellar lifetimes, evolution of stars, and star cluster ages.

Solution and grading rubric:
  • p:
    Correct. Understands that:
    1. stars in the same cluster are all born at the same time, but massive stars evolve faster than medium-mass stars, which evolve faster than low-mass stars (the "house party" analogy);
    2. medium-mass stars end their main-sequence lifetimes by becoming giants, planetary nebulae, and then white dwarfs;
    3. such that for medium-mass stars to have reached their end stage, massive stars have already gone through all their stages and have exploded as type II supernovae (and no longer appear on an H-R diagram), while low-mass stars have just begun their main-sequence life as red dwarfs.
  • 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. Typically at least understands correlation between mass and main-sequence lifetimes.
  • 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.
  • 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 30676
Exam code: midterm02n4s5
p: 3 students
r: 6 students
t: 10 students
v: 3 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1503) discussing the "house party model":

Another sample "p" response (from student 1758):

Astronomy midterm question: star cluster with type II supernovae?

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

Discuss which H-R diagram is more likely to be a star cluster with type II supernovae (which are deliberately not shown). Explain using the properties of mass and stellar lifetimes, evolution of stars, and star cluster ages.

Solution and grading rubric:
  • p:
    Correct. Understands that:
    1. stars in the same cluster are all born at the same time, but massive stars evolve faster than medium-mass stars, which evolve faster than low-mass stars (the "house party" analogy);
    2. massive stars end their main-sequence lifetimes by becoming supergiants, then explode as type II supernovae;
    3. such that for massive stars to have reached their end stage, medium-mass have just begun their main-sequence life, while low-mass stars have not yet begun their main-sequence life as red dwarfs.
  • 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. Typically at least understands correlation between mass and main-sequence lifetimes.
  • 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.
  • 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 30676
Exam code: midterm02sLoX
p: 11 students
r: 15 students
t: 23 students
v: 3 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 7074) discussing the "house party model":

Online reading assignment: Milky Way history, big bang clues (NC campus)

Astronomy 210, spring semester 2016
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 history of the Milky Way and big bang clues, a comic strip adaptation of of Neil deGrasse Tyson's "The Most Astounding Fact" 2008 interview for TIME magazine, and Minute Physics' video explanation of Olbers' paradox.


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.
"What I found intereating was that the early universe started out with just only hydrogen, and the first-generation massive stars then gathered this hydrogen and promptly got to work, fusing it into heavier elements in their cores, while their outer layers remained relatively pristine, free of metals (and the picture was really pretty)."

"The big bang, it is interesting to learn about the very beginning."

"The big bang was pretty neat. I've never really heard the lesson behind why it is possible."

"How they described telescopes as time machines."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Olber's question. I was reading it then lost interest."

"Metallicity was a little confusing to me."

"The big bang."

"Telescopes are time machines?"

"Metal-poor versus metal-rich."

"What I found confusing was the big bang theory. I found this more I guess you could say complicated in a way than confusing. I've just never understood how scientists can come up with some random theory. Theorys are based on facts and no one was able to witness this big bang. I don't know Ive always been curios about everything and question everything, well almost everything."

Indicate how the amount of these elements in the universe have changed over time.
(Only correct responses shown.)
Hydrogen: decreased [36%]
Metals (elements heavier than hydrogen and helium): increased [64%]

The outermost layers of __________ are more abundant in metals (elements heavier than hydrogen and helium).
extremely old stars that formed a long time ago.  **** [4]
young stars that formed very recently.  ****** [6]
(There is a tie.)  [0]
(Neither, as stars cannot have metals.)  [0]
(Unsure/guessing/lost/help!)  * [1]

Indicate what produced these elements.
(Only correct responses shown.)
Helium in the sun's core: the sun [18%]
Carbon in your body: another star, in the past [18%]
Calcium in your bones: another star, in the past [9%]
Iron in your blood: another star, in the past [18%]
Gold and silver from mines: another star, in the past [27%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I really don't know what to put down in this box anymore. Maybe I'll get creative for next weeks. :)"

20160502

Online reading assignment: Feynman diagram vertices

Physics 205B, spring semester 2016
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 presentations Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"The lines with arrows are matter particles. The wiggly line is a force particle which mediates electromagnetic interactions: it is the photon."

"Mostly just the basics of a Feynman diagram. The x-axis represents time and the y-axis represents direction. A straight line with a right-facing arrow is an electron, and straight line with a left-facing arrow is a positron, and a squiggly line is a photon. You can connect the straight lines as long as they also connect to a squiggly line, and all the pieces in a diagram have to be connected in some way, and there can't be any excess curves."

"Squiggles..."

"I'm fairly lost at this point."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"What I found confusing about this reading was trying to apply the chemistry to these diagrams that we are reading about. I can understand how these diagrams help explain decay sequences of particles. But I am just really trying to figure how I can draw one of these things for an actual reaction/decay. Also, I am starting to study for our midterm this upcoming Friday and I am still catching up with all of the magnetic stuff we've been talking about in class so I just really can't focus on this stuff, yet."

"I don't quite get all the rules for how to read the diagrams. More explanation on that would be great."

"Basically everything except the basics of the Feynman diagrams. I was horribly deceived into thinking that I would actually understand this stuff by the sentence near the beginning of the first post: "Particle physics: fun for the whole family.' Yeah right."

"I do not understand what 'annihilated by positron' is."

"What are we going to be applying this in class for? It's scary to ponder."

When reading Feynman diagrams, time runs from:
bottom to top.  * [1]
top to bottom.  [0]
left to right.  ******************************** [32]
right to left.  * [1]
(Unsure/guessing/lost/help!)  *** [3]

Describe how the path of an electron and the path of a positron are drawn differently on a Feynman diagram. (Note that both paths have the same "e" labels.)
"The path of an electron is drawn with its arrow pointing to the right, while the path of a positron is drawn with its arrow pointing to the left."

"I thought it was labeled e+ and e- for positron and electron respectively, but it would appear it can be labeled depending on the arrows as well."

"Not sure."

Describe what will happen if an electron meets a positron.
"They annihilate each other and produce energy?"

"They will annihilate each other and produce a photon."

"Boom! There goes the gamma ray."

The above (valid) Feynman diagram depicts an electron:
absorbing a photon.  * [1]
emitting a photon.  ******************************** [32]
annihilated by a positron.  ** [2]
(Unsure/guessing/lost/help!)  ** [2]

The above (valid) Feynman diagram depicts an electron:
absorbing a photon.  ***** [5]
emitting a photon.  ****** [6]
annihilated by a positron.  ************************ [24]
(Unsure/guessing/lost/help!)  ** [2]

The above (valid) Feynman diagram depicts an electron:
absorbing a photon.  ************************** [26]
emitting a photon.  ****** [6]
annihilated by a positron.  ** [2]
(Unsure/guessing/lost/help!)  *** [3]

Explain why the above Feynman diagram is invalid.
"Two elections do not form a photon. An electron can only emit a photon and then keep going."

"It says that two electrons come together to produce a photon which is (I hope) impossible."

"It violates rule number 2: 'You must have exactly one arrow going into the vertex and exactly one arrow coming out.'"

"I'm not really sure."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I only understood about 50% of the reading. Is that bad?"

"Seriously, can school be over?!?"

"I am freaking out a bit for the exam. Some of the material looks like from forever ago(?) and I have a calculus exam just before the physics exam. Trying not to have a panic attack."

"If we could just work on some review for the midterm, that'd be tight."

"Review pleassseeeee!"

20160501

Astronomy current events question: "Breakthrough Starshot" proposal

Astronomy 210L, spring semester 2016
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Geoff Brumfiel, "Stephen Hawking's Plan for Interstellar Travel Has Some Earthly Obstacles" (April 14, 2016)
npr.org/sections/thetwo-way/2016/04/14/474227319/stephen-hawkings-plan-for-interstellar-travel-has-some-earthly-obstacles
Theoretical physicist Stephen Hawking and Russian billionaire Yuri Milner proposed using a __________ to accelerate small spacecraft to the Alpha Centauri star system.
(A) giant laser.
(B) matter-antimatter reactor.
(C) fusion engine.
(D) hydrogen ramjet.
(E) reactionless thruster.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 23 students
(B) : 3 students
(C) : 12 students
(D) : 1 student
(E) : 3 students

Astronomy current events question: super-Earth 55 Cancri e climate

Astronomy 210L, spring semester 2016
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Felicia Chou and Whitney Clavin
, "NASA’s Spitzer Maps Climate Patterns on a Super-Earth" (March 30, 2016)
nasa.gov/press-release/nasa-s-spitzer-maps-climate-patterns-on-a-super-earth
NASA's Spitzer Space Telescope mapped the climate of super-Earth 55 Cancri e as it:
(A) emitted greenhouse gases.
(B) orbited around its star.
(C) erupted volcanically.
(D) changed its seasons.
(E) experienced erosion.

Correct answer: (B)

Student responses
Sections 30678, 30679, 30680
(A) : 6 students
(B) : 19 students
(C) : 6 students
(D) : 8 students
(E) : 3 students

Astronomy current events question: dark dwarf galaxy in gravitational lens SDP.81

Astronomy 210L, spring semester 2016
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Charles Blue
, "Dwarf Dark Galaxy Hidden in ALMA Gravitational Lens Image" (April 14, 2016)
public.nrao.edu/news/pressreleases/2016-sdp81-halo
A dark-matter dwarf galaxy was discovered by the Atacama Large Millimeter/submillimeter Array (ALMA) from how it __________ a more distant galaxy.
(A) cloaked.
(B) redshifted.
(C) sent back in time.
(D) destroyed.
(E) distorted.

Correct answer: (E)

Student responses
Sections 30678, 30679, 30680
(A) : 5 students
(B) : 7 students
(C) : 0 students
(D) : 3 students
(E) : 27 students