Online reading assignment: medium-mass stars, massive stars, neutron stars and black holes (SLO campus)

Astronomy 210, fall semester 2019
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 evolution of medium-mass stars, massive stars, neutron stars and black holes.

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.

"I found the car example to be really interesting. It's cool how we can relate real life things to this subject."

"How the stars can live off of helium after they have depleted all of their hydrogen."

"That helium fuses into heavier elements when it reaches a higher temperature of 100,000,000 K. Chemistry is my favorite subject and I was just very intrigued at that."

"Supernovas are fascinating because they are one of those 'doomsday' events that the sci-fi genre tends to romanticize."

"How in a binary star system, a dying star will begin 'eating' the fuel of its companion star. And if it 'eats' too quick it will explode and kill itself and its partner."

"How sad some white dwarf stars are alone. It's pretty depressing that they starve to death and die alone."

"That when medium-mass stars die they become white dwarfs, and then with a companion star go on to either become a nova or a type Ia supernova."

"The way a white dwarf can suck the hydrogen from a companion star is amazing."

"The death process of the stars, especially, the type II supernova. I did not know anything about how stars die, why they die, and what they become after death."

"Core implosion/explosion is very fun to learn about. I can imagine the outer layers of the star being gravitationally forced to crush the inner core. I can imagine that type II supernova star explosion being fairly colorful and dusty."

"I spent almost my entire high school career researching the death-cycle of stars for my senior project. WAY cool."

"That it would take forever watch something get into the black hole. And the spaghettification effect."

"How black holes can make bipolar jets! That's cool."

"I was always curious as to how black holes formed! They are just so... ominous. I would not want to get near one--they're freaky!"

"I thought this whole lesson was super-interesting, guess I'm goth-ier than I realized haha."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.

"Why a Hummer and a SmartCar can travel the same distance if a Hummer has a larger tank and a SmartCar has a smaller tank."

"Corresponding the correct end-of-life stage to the correct main-sequence star is a bit confusing at first because white dwarfs have technically low mass, but they become one after their medium-mass star depletes its hydrogen and becomes a giant that turns into a white dwarf after all its energy has been exerted."

"Why do massive stars eat anything they can to survive but smaller stars won't eat as much junk?"

"I need more explanation on a star's death and the phases the star takes as it dies."

"How it is possible for a white dwarf (with a companion star) to either flash-fuse or just simply explode. How can it do one or the other? Wouldn't it just do one every time?"

"As much as black holes intrigued me, they also confused the hell out of me. Trying to understand the physics of it all was pretty difficult."

"Time slowing when approaching a black hole's event horizon."

"I'm having trouble wrapping my head around the idea of black holes--why they can't be seen, event horizons, space-time, etc."

"Why the space-time grid is always depicted as a flat surface. I just don't get we they do that. Is it to make it easier to conceptualize?"

"When talking about black holes in space, I understand that we would be able to feel a black hole because of the gravitational pull inward toward it. I'm confused about how the black hole effects space-time."

"A bit of everything since it's all so much to take in."

"Nothing particularly was confusing."

A Hummer H2 and a SmartCar ForTwo can travel the same distance with a full tank of gas. Briefly explain how this is possible.

"The fuel usage for a SmartCar is way lower than the fuel usage of a Hummer, but a Hummer has way more fuel available to it than the SmartCar."

"A Hummer has a larger tank with lower gas mileage while the SmartCar has a smaller tank with higher gas mileage. These factors balance each other out between the two cars and give them both the same traveling distance."

"The Hummer could have a bigger gas tank than the SmartCar. And the SmartCar would have better gas mileage."

"The Hummer can hold a lot of gallons of gas, but it burns through it very quickly (bad gas mileage). A SmartCar doesn't hold very many gallons but burns through it very slowly (good gas mileage)."

"I'm kind of confused on how to explain this. It didn't make sense to me at all."

Match the end-of-life stage with the corresponding main-sequence star.
(Only correct responses shown.)

Black hole: massive main sequence star [92%]
Neutron star: massive main sequence star [76%]
White dwarf: medium-mass main-sequence star [80%]
(No stellar remnant observed yet): low-mass main-sequence star [72%]

Match the type of explosion (if possible) with the corresponding main-sequence star.
(Only correct responses shown.)

Type II supernova: massive main sequence star: [88%]
Type Ia supernova: medium-mass main-sequence star [92%]
Nova: medium-mass main-sequence star [56%]
Low-mass main-sequence star: (no explosion possible) [56%]

If you were to leap into a black hole, your friends would typically watch you falling in for __________ before you entered the event horizon.

seconds.	* [1]
hours.	** [2]
days.	* [1]
a year.	[0]
many years.	* [1]
forever.	***************** [17]
(Unsure/guessing/lost/help!)	*** [3]

The first rule of astronomy class is...

"Show interest in space."

"Observe the world around you."

"To actually show up and attend class!"

"Don't procrastinate."

"Question everything you thought you knew."

"Read the syllabus and get your starwheel."

"I'm not too sure. Show up early? Wear old clothes? Bring a sledgehammer?"

"A foot-measuring device is for feet only."

"I feel like this was a trick question and I searched the text for it, but ultimately just ended up confused. The first rule is to learn to the best of your abillity?"

"You do not talk about astronomy class."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I need a lot of explanation on the main sequence stars and explosions, plus how the lifetimes work."

"Dying stars are cool."

"Was our solar system (planets, asteroids, etc.) created by another star or from our sun? If by a different star, where is that star now?" (Anything other than hydrogen in our solar system was created by massive stars that exploded a long time ago (we don't know where those first-generation stars that lived and died are anymore). Then when our sun starting forming out of unused hydrogen from those previous stars, it gathered up the elements created by those stars around it to make the planets. #deepthoughts)

"Talk about black holes, I can't get enough."

"'Spaghettification' is my new favorite word."

"Do you like Star Wars? (Well, probably just the original trilogy. And maybe Rogue One.)"

"What is "nothing"? Can there be such a thing? I just watched '2013 Isaac Asimov Memorial Debate: The Existence of Nothing' and now my brain hurts and I'm not satisfied with the answers given there." (Now you're making my brain hurt. #deepthoughts)

Online reading assignment: elasticity

Physics 205A, fall semester 2019
Cuesta College, San Luis Obispo, CA

Students have a bi-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 a presentation on elasticity.


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.

"Tension is when you stretch something as opposed to compression when you squish something. Stress is the applying force to the object and strain is a measure of how the object/material responds."

"The two cases of elasticity, either with a tension force or a compression force. Tensile/compressive stress is the act of applying the force, whereas tensile/compressive strain is how the material behaves under tension/compression."

"When compressing a spring, or when it restores, the displacement of the spring is proportional to the force applied. Also, the tensile force is perpendicular to the area, and the shearing force is parallel with a surface."

"That k is the spring constant and x is the displacement of the spring from its unstrained length. The minus sign indicates that the restoring force always points in an opposite direction to the displacement of the spring from its length."

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.

"Nothing is too confusing to grasp from the text. Just a few equations that are used in certain circumstances."

"Hooke's law. I don't understand how materials with a material-dependent Young's modulus (in units of pascals) that characterizes the response of the material to these stresses."

"Using Hooke's law, and why exactly strain is unitless."

"From the presentation preview I was first confused about the tensile stress example but upon another glance I was able to understand it. The stress causes the object to stretch to a limit that does not cause it to break."

"Putting the complex theories into practical world applications and making the connection to conceptualizing while using the equations correctly."

"The elastic deformation equation is a little confusing because I'm not sure about all the components and variables."

"I don't understand hardly anything, I don't know what the variables stand for."

What is the SI (Système International) unit for stress?

"N/m²."

"Pa."

Explain why strain is a unitless quantity.

"Strain is unitless because it is a proportion of two quantities with the same dimensions."

"It's a unitless quantity because it deals with the fractional change of length or volume."

"I am not sure."

"I don't know."

What is the SI (Système International) unit for Young's modulus?

"N/m²."

"Pa."

The __________ lengths of vertical suspension bridge cable are stretched by a greater amount ∆L from their original lengths.

shorter.	***** [5]
longer.	**************************** [28]
(There is a tie.)	*** [3]
(Unsure/lost/guessing/help!)	***** [5]

The __________ columns of 2×4s support the least amount of force.

narrower (two 2×4s).	****************** [18]
wider (three 2×4s).	******** [8]
(There is a tie.)	********** [10]
(Unsure/lost/guessing/help!)	***** [5]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Need some clearing up, book kind of went off the rails."

"Please go over these in class, I am confuuuuuused ):"

"I understand that Young's modulus is the ability of a material to withstand changes in length when under tension. Will this value always be provided for an individual material? Does it matter what the material is resting on... for example a piece of steel on concrete vs a wood table?" (Yes, the Young's modulus values will always be given for a problem (unless you need to solve for it); and no, it doesn't matter what the material (being tested) is resting on, provided that the supporting object is strong enough to handle whatever is being done to the material being tested.)

"Will we be doing a simple harmonic motion lab?" (Yes, for Lab 12.)

I don't have anything to say."

"Yay physics :)"

"I'm just enjoying the day."

"This irregular weather is killing me."

Online reading assignment: medium-mass stars, massive stars, neutron stars and black holes (NC campus)

Astronomy 210, fall semester 2019
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 evolution of medium-mass stars, massive stars, neutron stars and black holes.


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.

"How a low-mass star will take much longer to run out of hydrogen to fuse. How does it take longer, since it's smaller? "

"How a Hummer and SmartCar are able to travel same distance even with the Hummer having a larger tank."

"The lifetimes of the stars. I just find it cool how it's the bigger stars that burn out and die off the quickest compared to the small stars who live on for much longer."

"In a long time the sun will eventually expand into a red giant and that is when Earth will come to an end."

"That a star's mass determines what happens when the star runs out of fuel, and what type of 'corpse' it will become after its death."

"That when a star is about to die it goes into 'starvation' mode."

"Learning more about stars like our own really puts our existence into some perspective."

"That different mass stars die different ways, because I had just assumed that they would just stop glowing, but I was way wrong."

"The types of supernovas/novas, because those were cool images."

"Black holes."

"Black holes are invisible, kinda ominous and scary, but interesting nonetheless."

"The escape velocity of a black hole blows my mind that even light cannot escape."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.

"How convection currents work internally in the stars."

"I'm confused about binary systems and how they keep going even after the nova that occurs from the white dwarf."

"I'm not grasping the different types of supernovas/novas."

"The lighthouse model! What is it trying to explain?"

"Black holes and neutron stars. I don't know the models made a little sense but I think spending a little more time on it and further explanation on it that would help because I am a little lost."

"How a black hole works."

"Nothing in particular."

A Hummer H2 and a SmartCar ForTwo can travel the same distance with a full tank of gas. Briefly explain how this is possible.

"The Hummer H2 has a bigger gas tank but uses it faster. The SmartCar has a smaller gas tank and uses it slower."

"The Hummer has lower mileage than the SmartCar but, it has a bigger fuel tank."

"It's possible because the SmartCar has better fuel efficiency with its smaller tank."

"I honestly don't know; I'm slightly confused."

"Don't know yet."

Match the end-of-life stage with the corresponding main-sequence star.
(Only correct responses shown.)

Black hole: massive main sequence star [76%]
Neutron star: massive main sequence star [59%]
White dwarf: medium-mass main-sequence star [53%]
(No stellar remnant observed yet: low-mass main-sequence star [35%]

Match the type of explosion (if possible) with the corresponding main-sequence star.
(Only correct responses shown.)

Type II supernova: massive main sequence star: [88%]
Type Ia supernova: medium-mass main-sequence star [82%]
Nova: medium-mass main-sequence star [35%]
Low-mass main-sequence star: (no explosion possible) [53%]

If you were to leap into a black hole, your friends would typically watch you falling in for __________ before you entered the event horizon.

seconds.	** [2]
hours.	* [1]
days.	[0]
a year.	[0]
many years.	* [1]
forever.	********** [10]
(Unsure/guessing/lost/help!)	*** [3]

The first rule of astronomy class is...

"Persistence?"

"Ask questions?"

"Earth is flat?"

"To build telescopes?"

"Come to each and every class?"

"Dome prepared and ready to learn?"

"Look up at the stars, because that is where the answers are?"

"You do not talk about astronomy class.' (Fight Club, 1999)"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"How are cars related to astronomy?"

"For a medium-mass star, how come the convection current doesn't work in the similar way a low mass star works?" (Convection is a surface effect for a star, so for a medium-mass or massive star, convection (the "miso soup effect") is right at the "skin" of those stars. However, for a low mass star, it is so small that the "skin" and core are basically touching, such that the convection currents are able to affect the core.)

"What is space-time and how can gravity affect it?"

"I'd like to go over black holes a bit more."

"Will we get into black holes more or will we just get a brief talk about them?

"Have humans ever sent anything into a black hole?" (No, but we have observed stars being shredded apart as they get too close, and their material falls in towards black holes.)

"Can you please go over these slides in class, there was a lot, thank you."

Online reading assignment: ideal fluid flow

Physics 205A, fall semester 2019
Cuesta College, San Luis Obispo, CA

Students have a bi-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 a presentation on ideal fluid flow.


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.

"Fluid flow can be steady or unsteady. Velocity at any point is constant as time passes for a steady flow. Unsteady flow exists whenever the velocity at a point in the fluid changes as time passes. Fluids can also be compressible or incompressible, most being nearly incompressible. Fluid flow can be viscous or nonviscous. A viscous fluid does not flow readily but a non-viscous one, like water, does."

"Ideal fluid flow has the following characteristics; incompressible, laminar, and non-viscous. I understand how volume flow rate conservation law that comes from its incompressible nature uses the continuity equation. And how the energy density conservation law uses Bernoulli's equation."

"Fluid flow can be steady or unsteady; Unsteady flow exists whenever the velocity at a point in the fluid changed as time passes, Turbulent flow is an extreme kind of unsteady flow and occurs when there are sharp obstacles or bends in the path of a fast moving fluid. Fluid can be compressible or incompressible, fluid flow can be viscous or non-viscous."

"I understand that when an ideal fluid flows through a pipe with a widening cross sectional area, the velocity of the fluid will slow down, kinetic energy decreases and the pressure will increase. When an ideal fluid flows through a pipe with a narrowing cross sectional area, the velocity of the fluid will increase, kinetic energy is increases and the pressure will decrease."

"As the area decreases the fluid speed increases. when elevation decreases the fluid speed also increases. Bernoulli's equation relates the density, pressure, fluid speed and elevation at two separate points."

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.

"I seemed to understand this subject, but completely differentiating between the properties of ideal fluid flow will need more practice. What seemed somewhat confusing or a little more review in class are volume flow conservation and energy density conservation, and exactly how to apply the continuity equation to volume flow rate conservation law and the Bernoulli's equation to energy density conservation law."

"Bernoulli's equation definitely seems ominous. I can see the relation between energy conservation and this topic. However, hopefully after the homework problems I'll be more comfortable with it."

"I am confused about when to use Bernoulli's equation and how the concepts of the work-energy theorem relates to this equation. I am confused by what is meant by how elevation changes the various variables as well."

"I don't understand when the pressure or density changes, or how to know when y changes, how that works with/ against the change in area. I dont understand how to calculate anything, lost :("

"I didn't quite understand Bernoulli’s equation. The equations itself looked very complicated and when the book didn’t really provide an example problem and I feel like I just learn better that way so maybe that’s why I feel like I didn’t understand how to use the equation."

"This chapter seemed to hold a mess of equations that I don't know when to use or how to use them; however, it seems similar to the set-up of our previous conservation equations in which we ignore one side of the equation and can determine whether each piece on the right side of the equation is increasing or decreasing."

"How Bernoulli's equation relates to the work-energy theorem."

"I don't understand anything yet."

What is the SI (Système International) unit for volume flow rate?

"m³/s."

For an ideal fluid flowing through a pipe with a constant cross-sectional area, the volume flow rate ∆V/∆t:

decreases.	[0]
remains constant.	**************************************** [40]
increases.	**** [4]
(Unsure/lost/guessing/help!)	** [2]

For an ideal fluid flowing through a horizontal pipe with an increasing cross-sectional area, the volume flow rate ∆V/∆t:

decreases.	************************* [25]
remains constant.	********* [9]
increases.	********** [10]
(Unsure/lost/guessing/help!)	** [2]

For an ideal fluid flowing through a horizontal pipe with a decreasing cross-sectional area, the volume flow rate ∆V/∆t:

decreases.	********** [10]
remains constant.	******* [7]
increases.	*************************** [27]
(Unsure/lost/guessing/help!)	******* [2]

For an ideal fluid flowing through a pipe with a widening cross-sectional area, indicate the changes in each of fluid flow parameters.
(Only correct responses shown.)

(1/2)·ρ·∆(v²): decreases [54%]
ρ·g·∆y: no change [52%]
∆P: increases [33%]

For an ideal fluid flowing through a pipe with a narrowing cross-sectional area, indicate the changes in each of fluid flow parameters.
(Only correct responses shown.)

(1/2)·ρ·∆(v²): increases [57%]
ρ·g·∆y: no change [54%]
∆P: decreases [37%]

For an ideal fluid flowing through a descending pipe with a constant cross-sectional area, indicate the changes in each of fluid flow parameters.
(Only correct responses shown.)

(1/2)·ρ·∆(v²): no change [89%]
ρ·g·∆y: decreases [33%]
∆P: increases [74%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"If cross-sectional area is changing, do we assuming that particles are still moving in a straight line with no vertical deviation?" (Yes, if flow is laminar all the streamlines will be parallel to each other, either scrunching together or spacing apart without crossing. #whateveryoudodontcrossthestreams.)

"Great presentation GIFs. Super-helpful for understanding the material."

"Your drawings make everything better. shout out to visual learners."

"Go over these as you normally do, thank you!"

"Now you know why I don't want to be a physics major. I want to just live my life with plants and dirt."

Astronomy quiz question: comparing star distances from apparent magnitudes, absolute magnitudes

Astronomy 210 Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA

The apparent magnitudes and absolute magnitudes of three stars are listed below.

	m apparent magnitude	M absolute magnitude
Aldebaran	+0.9	–0.6
Capella Ab	+0.9	+0.4

The star that is farthest away from Earth is:
(A) Aldebaran.
(B) Capella Ab.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

Aldebaran appears to have a brightness of +0.9 as seen from its actual location from Earth, but when placed at the "fair" distance of 10 parsecs away, it becomes brighter (–0.6). This means that Aldebaran was brought closer to Earth when moved to 10 parsecs, and thus is located farther than 10 parsecs away from Earth.

Similarly, Capella Ab appears to have a brightness of +0.9 as seen from its actual location from Earth, but when placed at the "fair" distance of 10 parsecs away, it also becomes brighter (+0.4), and must also be located farther than 10 parsecs away from Earth.

However, because Aldebaran's increase in brightness when brought to 10 parsecs was greater than Capella Ab's increase in brightness, then Aldebaran's actual location is further out from 10 parsecs (and farther away from Earth) than Capella Ab.

Section 70158
Exam code: quiz05Sh0w
(A) : 21 students
(B) : 6 students
(C) : 1 student
(D) : 1 student

Success level: 73% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50

Section 70160
Exam code: quiz05NpRm
(A) : 9 students
(B) : 8 students
(C) : 3 students
(D) : 2 students

Success level: 44% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.38

Astronomy quiz question: hottest star?

Astronomy 210 Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA

Which star is the hottest?
(A) A5 main sequence star.
(B) F0 supergiant.
(C) B5 white dwarf.
(D) M0 red dwarf.
(E) (There is a tie.)

Correct answer (highlight to unhide): (A)

An H-R diagram is provided with this quiz.


These stars are plotted on an H-R diagram below. The M0 red dwarf is the coolest, followed by the F0 giant, A5 main-sequence star, and the B5 white dwarf is the hottest, with a temperature of just under 20,000 K.


Section 70158
Exam code: quiz05Sh0w
(A) : 1 student
(B) : 2 students
(C) : 22 students
(D) : 2 students
(E) : 1 student

Success level: 77% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75

Astronomy quiz question: A5 white dwarf vs. G5 supergiant

Astronomy 210 Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA

An A5 white dwarf has a ___________ than a G5 supergiant.
(A) brighter luminosity.
(B) larger size.
(C) hotter temperature.
(D) (Two of the above choices.)
(E) (All of the above choices.)
(F) (None of the above choices.)

Correct answer (highlight to unhide): (C)

An H-R diagram is provided with this quiz.


These stars are plotted on an H-R diagram below. The A5 white dwarf has a hotter temperature, but a dimmer luminosity and smaller size than the G5 supergiant.


Section 70158
Exam code: quiz05Sh0w
(A) : 2 students
(B) : 1 student
(C) : 20 students
(D) : 3 students
(E) : 2 students
(F) : 1 students

Success level: 70% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75

(Cf. a re-worded version of this same question: "A G5 supergiant has a ___________ than an A5 white dwarf.")

Astronomy quiz question: B5 main sequence star vs. M5 giant

Astronomy 210 Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA

A B5 main sequence star and an M5 giant could have the same:
(A) luminosity.
(B) size.
(C) temperature.
(D) (Two of the above choices.)
(E) (All of the above choices.)
(F) (None of the above choices.)

Correct answer (highlight to unhide): (A)

An H-R diagram is provided with this quiz.


These stars are plotted on an H-R diagram below. The B5 main sequence star has a smaller size and a hotter temperature than the M5 giant, but they could have the same luminosity.


Section 70158
Exam code: quiz05Sh0w
(A) : 22 students
(B) : 1 student
(C) : 0 students
(D) : 2 students
(E) : 1 student
(F) : 3 students

Success level: 77% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.63

Astronomy quiz question: smallest star?

Astronomy 210 Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA

Which star is the smallest?
(A) B5 white dwarf.
(B) M0 red dwarf.
(C) A5 main sequence star.
(D) F0 supergiant.
(E) (There is a tie.)

Correct answer (highlight to unhide): (A)

An H-R diagram is provided with this quiz.


These stars are plotted on an H-R diagram below. The F0 supergiant is the largest, followed by the A5 main-sequence star, M0 red dwarf, and the B5 white dwarf is the smallest, with a radius of just over 0.01× the radius of the sun.


Section 70160
Exam code: quiz05NpRm
(A) : 13 students
(B) : 8 students
(C) : 1 students
(D) : 0 students
(E) : 0 students

Success level: 63% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): –0.05

Astronomy quiz question: G5 supergiant vs. A5 white dwarf

Astronomy 210 Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA

A G5 supergiant has a ___________ than an A5 white dwarf.
(A) brighter luminosity.
(B) larger size.
(C) hotter temperature.
(D) (Two of the above choices.)
(E) (All of the above choices.)
(F) (None of the above choices.)

Correct answer (highlight to unhide): (D)

An H-R diagram is provided with this quiz.


These stars are plotted on an H-R diagram below. The G5 supergiant has a brighter luminosity, larger size, but a cooler temperature than the A5 white dwarf.


Section 70160
Exam code: quiz05NpRm
(A) : 1 student
(B) : 1 student
(C) : 0 students
(D) : 12 students
(E) : 6 students
(F) : 2 students

Success level: 56% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.71

(Cf. a re-worded version of this same question: "An A5 white dwarf has a ___________ than a G5 supergiant.")

Astronomy quiz question: B5 supergiant vs. K5 main sequence star

Astronomy 210 Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA

A B5 supergiant and a K5 main sequence star could have the same:
(A) luminosity.
(B) size.
(C) temperature.
(D) (Two of the above choices.)
(E) (All of the above choices.)
(F) (None of the above choices.)

Correct answer (highlight to unhide): (F)

An H-R diagram is provided with this quiz.


These stars are plotted on an H-R diagram below. The B5 supergiant has a brighter luminosity, larger size, and a hotter temperature than the K5 main sequence star.


Section 70160
Exam code: quiz05NpRm
(A) : 5 students
(B) : 0 students
(C) : 0 students
(D) : 2 students
(E) : 1 student
(F) : 14 students

Success level: 66% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.57

Astronomy quiz archive: sun/spectra/star properties

Astronomy 210 Quiz 5, fall semester 2019
Cuesta College, San Luis Obispo, CA

Section 70158, version 1
Exam code: quiz05Sh0w


Section 70158

0- 8.0   :
8.5-16.0 :	*** [low = 10.0]
16.5-24.0 :	*
24.5-32.0 :	********* [mean = 32.0 +/- 8.2]
32.5-40.0 :	******************* [high = 40.0]

Section 70160, version 1
Exam code: quiz05NpRm


Section 70160

0- 8.0   :
8.5-16.0 :	* [low = 16.0]
16.5-24.0 :	**********
24.5-32.0 :	***** [mean = 26.0 +/- 7.5]
32.5-40.0 :	****** [high = 40.0]

Online reading assignment: fusion, nebulae, star cluster ages (SLO campus)

Astronomy 210, fall semester 2019
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 fusion, nebulae, and star cluster ages.


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.

"I'm excited to learn more about how fusion works. It just seems cool."

"How fusion only happens in the core of a star."

"I appreciated the cheerleader analogy, it actually really helped to be able to visualize what's happening at the sun's core."

"It is fascinating that lower-mass stars last longer than the current age of our universe, although it makes sense because, effectively, they are 'burning' slower."

"I thought it was funny that big stars burn out faster. For some reason reminded me of sumo wrestlers."

"Luminosity depends on mass for only main sequence stars--I thought that would apply for all stars."

"I just found how main sequence stars are ordered by mass, however the other stars (giants, super giants, and white dwarfs) aren't. It just caught my attention."

"That after a star runs out of hydrogen it dies :("

"It's amazing that there is so much matter in space, I thought it was just empty space."

"I thought the nebulae were super-cool (and super pretty). It's kinda weird to think about there being 'clouds' in space, I like it though."

"That nebulae are different colors due to the way photons interact with gas/dust."

"How the different components of nebulae determine their colors."

"I found that when there are a cluster of stars and when dust is around from the stars they turn into little planets around the star. This was interesting to me because when you look at the picture of the star cluster it just looks like a bunch of stars."

"Supernovae are interesting because they can 'kickstart' the formation of new stars."

"Star formation was one of the things I was most curious about coming into this class. It's interesting to learn about the process."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.

"Fusion because there's big words and I am tired so my brains not really working if I'm being honest."

"I find the H-R diagram to be confusing at times. I think it has to do with the multitude of variables displayed. I thought I had it figured out last class, but then certain stars break from the mass-luminosity relationship. Conceptually that might have thrown me off some. My plan to further my understanding is to maybe ask for a walkthrough in class."

"I found the plotting of the other stars off the main-sequence a bit confusing because there's no correlation between their mass and luminosity."

"The main sequence lifetimes for different sizes of stars confused me for a little bit because I read it wrong when I first read it. At first I though the bigger stars would stick around the longest."

"Hydrostatic equilibrium and fusion."

"I'm not super-confused but would just like more practice with determining what is and isn't in a nebula."

"Learning about the different types of nebulae was a bit confusing for me. For the reflection nebula, it's hard for me to imagine how the cloud filters out the certain colors from the star hitting it. I don't understand how these nebulae behave differently in space based on their composition."

"The H-R diagram doesn't make sense to me, but I think I understand the house party model?"

"I don't understand the H-R diagram; specifically the turn-off point."

"It's all rather hard to grasp."

"Nothing in particular, what I read made sense to me. "

"I didn’t find anything confusing."

Rank the luminosities of these main-sequence stars (1 = brightest, 3 = dimmest). (There are no ties.)
(Only correct responses shown.)

Massive: brightest luminosity [100%]
Medium-mass (sunlike): medium luminosity [96%]
Low mass (red dwarf): dimmest luminosity [96%]

Rank the fusion rates of these main-sequence stars (1 = fastest, 3 = slowest). (There are no ties.)
(Only correct responses shown.)

Massive: fastest fusion rate [78%]
Medium-mass (sunlike): medium fusion rate [96%]
Low mass (red dwarf): slowest fusion rate [81%]

Fusion requires high temperatures in order for nuclei to move quickly enough to:

break heavy elements apart.	***** [5]
create convection currents.	*** [3]
overcome gravity.	** [2]
overcome repulsion.	*************** [15]
(Unsure/guessing/lost/help!)	** [2]

Briefly explain why "cold fusion" (producing energy from hydrogen fusion at room temperature) would be implausible.

"Because it is much more effective at higher temperatures. The collisions between nuclei would not happen at room temperature."

"Fusion requires high pressure and temperatures. When pressure and temperatures are low, then hydrogen does not get squeezed as much and it moves too slowly to collide with one another."

"Because hydrogen can only be fused if it is moving very fast and under lots of pressure for enough force to overcome proton-proton repulsion."

"The amount of pressure required would be ridiculous."

Match the three different types of nebulae with their colors.
(Only correct responses shown.)

Emission: pink [93%]
Reflection: blue [93%]
Dark: brown/black [100%]

Match the three different types of nebulae with their composition.
(Only correct responses shown.)

Emission: hydrogen [96%]
Reflection: small dust particles [100%]
Dark: large dust particles [96%]

Rank the lifetimes of these main-sequence stars (1 = shortest, 3 = longest). (There are no ties.)
(Only correct responses shown.)

Massive: shortest main-sequence lifetime [67%]
Medium-mass (sunlike): medium main-sequence lifetime [96%]
Low mass (red dwarf): longest main-sequence lifetime [70%]

If there was an open invitation to a house party (no specific time given), when would you show up?

Early, or on time.	***** [5]
When the most people should be there.	********************* [21]
After most everyone has left.	* [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Why aren't the other types of stars ordered in terms of their masses on the H-R diagram?" (Because they're dying or dead stars that ran out of hydrogen in their cores.)

"I need more help on the H-R diagram and the mass and luminosity stuff."

"The H-R diagram is a little confusing to tell which stars have a higher/lower luminosity. From what I read the bottom stars have less right?" (Correct.)

"How do stars form from dust clouds? Or is it the hydrogen in the dust clouds that forms the stars? where does the dust come from in the first place?" (The universe started out with just hydrogen, which formed the first stars. Then after the stars fused hydrogen into other stuff, they they exploded, such that when subsequent stars can form (from the remaining unused hydrogen), planets can form around them from the "dust" that was produced from the previous generation.)

"My mind was blown when they said that there are more stars than grains of sand on Earth. That's insane! What's the method for counting all the grains of sand though?" (Count how many grains of sand in a handful; then estimate how many handfuls of sand there are...)

"So, when the Enterprise hides in a nebula from a Klingon warship (in the movie Star Trek II: The Wrath of Khan), wouldn't it be best for it to be a dark nebula, with the large clumpy dust particles? But then it shouldn't have looked like a big glowing cloud, right?" (You sound like you know way too much astronomy.)

"I found dark nebulas to be interesting. When I was thinking about it, the night sky is already dark. If you look at a long exposure photograph you could then see these dark clusters called dark nebulas. It's amazing that they are completely blocking a viewer on Earth from seeing some stars because of their thick dust clouds. My question is, can you see them with the naked eye, or only through photographs? I feel like I would have noticed a patch of the night sky missing by now." (There aren't any big dark nebulae close for us see them with the naked eye noticeably blocking stars, but if you do a time exposure so you can see faint, distant stars, you can make out a variety of dark nebulae that block out those really faint stars; those dark nebulae especially stand out with the Milky Way as a background.)

"Can a supernova be the birthplace of a black hole?" (It is, specifically a type II supernova.)

"Would you ever actually have a house party with your students to see who was truly honest about their answer on this assignment?" (That sounds like a science experiment to me.)

"You have any fun plans for Halloween?" (Mrs. P-dog and I celebrate Madonnaween.)

Online reading assignment: static fluids

Physics 205A, fall semester 2019
Cuesta College, San Luis Obispo, CA

Students have a bi-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 a presentation on static fluids.


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.

"Mass density is mass of a substance divided by its volume."

"Pressure as force density is force divided by area. Pressure as energy density is energy divided by volume."

"The concept of pressure being force over surface area. As well as energy density conservation. If the surrounding pressure of an object increases then the ρ·g·∆y of the object will decrease and vice versa. As for the buoyant force, it's all dependent on the object's volume and the density of the fluid it is submerged in."

"That pressure and gravitational potential energy have an inverse relationship. So, for example, as a submarine goes further underwater in the y direction, its pressure increases while its gravitational potential energy decreases. The opposite is true for a balloon flying into the sky."

"In the example of a swimmer fully submerged underwater, I understand the application of Newton's first law in that all the forces acting on the swimmer balance out. This is given by the two forces of a downward weight force and upwards buoyant force balancing out."

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.

"After going through the presentation preview, I was confused about the fluid density at first but then took another glance and realized that it is simply the kilograms divided by meters cubed because it is a 3D object it must be cubed."

"Something I didn't understand from the reading is pressure and depth in a static fluid. I don't understand the formula. I need an example of how to use it and what the variables mean."

"I was a little confused about the concept of buoyancy. I could definitely use some review of that equation."

"Archimedes' principle is a little confusing. When we draw our diagrams do we treat it as we would a normal force? Also, I feel like the book did a bad job at explaining some of this stuff. None of it seems too difficult by any means."

"The units and some equations that you use when looking at the problems. Hopefully will go over in class to clarify."

What is the numerical value for atmospheric pressure (P_atm, at sea level), in units of Pa?

"101,325 Pa."

"1.013 × 10⁵ Pa, which is also 1 atm."

To three significant digits, what is the numerical value for the density of water, in units of kg/m³?

"1,000 kg/m³."

To two significant digits, what is the numerical value for the density of air (at 20° C), in units of kg/m³?

"1.2 kg/m³."

For the air pressure surrounding the balloon as it rises from ground level to the upper atmosphere, indicate the changes in each of the energy density forms of the atmosphere.
(Only correct responses shown.)

ρ_air·g·∆y: increases [61%]
∆P: decreases [56%]

For the water pressure that surrounded these cups as they were taken deep underwater, indicate the changes in each of the energy density forms of the water.
(Only correct responses shown.)

ρ_water·g·∆y: decreases [44%]
∆P: increases [66%]

For the submerged diver floating underwater, Newton's __________ law applies, and the (downwards) weight force and (upwards) buoyant force on the diver are __________.

first; balanced.	******************************** [32]
second; unbalanced.	****** [6]
(Unsure/lost/guessing/help!)	*** [3]

Using ρ·g·V, the density of the __________ should be included in the calculation of the magnitude of the buoyant force on the diver.

diver.	*********** [11]
water.	*************************** [27]
(Unsure/lost/guessing/help!)	*** [3]

For the red ship (barely) afloat, Newton's __________ law applies, and its (downwards) weight force, the (downwards) oil platform's weight force, and the (upwards) buoyant force on the red ship are __________.

first; balanced.	**************************** [28]
second; unbalanced.	********** [10]
(Unsure/lost/guessing/help!)	*** [3]

Using ρ·g·V, the density of __________ should be included in the calculation of the magnitude of the buoyant force on the red ship.

seawater.	*********************** [23]
air.	** [2]
red ship.	************ [12]
(Unsure/lost/guessing/help!)	**** [4]

Using ρ·g·V, the volume of the red ship's __________ should be included in the calculation of the magnitude of the buoyant force on the red ship.

underwater portion.	*********************** [23]
above water portion.	** [2]
total volume, both underwater and above water.	************* [13]
(Unsure/lost/guessing/help!)	[3]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Please go over these!"

"I would love if we could spend a generous amount of time calculating different pressures."

"Yikes! These were challenging for me. Hopefully I will feel better about this material after lecture."

"I do not understand the concept behind the red ship's buoyancy and I am having a hard time understanding the reasoning behind the formulas."

"Are we given the equations on the tests?" (Yes--you can see which equations were given on past quizzes and exams, so you wouldn't need to memorize those.)