Astronomy midterm question: comparing sizes, temperatures of same-luminosity stars

Astronomy 210 Midterm 2, fall semester 2019
Cuesta College, San Luis Obispo, CA

The following claim was made by a student on an astronomy exam[*]:

2881: If two stars have the same luminosity, the star with the lower temperature must be larger.

Discuss whether this claim is correct or incorrect, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

[*] waiferx.blogspot.com/2009/05/astronomy-midterm-question-cooler.html.

Solution and grading rubric:

• p:
  Correct. Discusses how the H-R diagram and/or the Stefan-Boltzmann law (luminosity is proportional to size × Temperature⁴) demonstrates that in order for a cooler star to have the same luminosity as a hotter star, its lower temperature must be compensated for by having a larger size; thus the claim by that student is correct.
  
• 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. At least attempts to use Wien's law, the Stefan-Boltzmann law, and/or H-R diagram. May have argument based on the size of a star being dependent on luminosity and temperature.
  
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion not clearly based on Wien's law, the Stefan-Boltzmann law, and/or H-R diagram.
  
• y:
  Irrelevant discussion/effectively blank.
  
• z:
  Blank.
  

Grading distribution:
Section 70158
Exam code: midterm02Rf0w
p: 31 students
r: 1 student
t: 0 students
v: 1 student
x: 1 student
y: 0 students
z: 0 students

Section 70160
Exam code: midterm02T4qz
p: 16 students
r: 2 students
t: 0 students
v: 2 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 0809), using the Stefan-Boltzmann law:
A sample "p" response (from student 1234), using a Hertzsprung-Russell diagram:
A sample "p" response (from student 1278) using both the Stefan Boltzmann law and a Hertzsprung-Russell diagram:
A sample "x" response (from student 4000), appealing to concepts other than than of the Stefan-Boltzmann law:

Astronomy quiz archive: stellar evolution

Astronomy 210 Quiz 6, fall semester 2019
Cuesta College, San Luis Obispo, CA

Section 70158
Exam code: quiz06sOr6


Section 70158

0- 8.0 :
8.5-16.0 :	**** [low = 13.5]
16.5-24.0 :	******
24.5-32.0 :	************ [mean = 27.5 +/- 6.9]
32.5-40.0 :	************ [high = 36.5]

Section 70160
Exam code: quiz06NyQ7


Section 70160

0- 8.0 :
8.5-16.0 :	****** [low = 11]
16.5-24.0 :	****** [mean = 21.7 +/- 6.8]
24.5-32.0 :	*******
32.5-40.0 :	** [high = 33]

Online reading assignment: the Milky Way (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 Milky Way's shape, size and composition and spiral arm structure and formation.


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 really liked the Fe[26] game, I may or may not have spent half an hour playing it when I should've been studying."

"I didn't think about the fact that we can not see the rest of our galaxy from our perspective."

"I find it interesting that if we use an infrared or radio telescope that we can see the whole Milky Way galaxy and if we don't do this we cannot see as much of it."

"Learning a bit about dark matter in the Milky Way was interesting. I had no idea that dark matter is what creates and spreads out the gravity in our galaxy. This unusual matter that does not deal with light or dust or gas is holding our galaxy together."

"Dark matter, thinking about the majority of matter is not seen/doesn't interact with our realm of reality is fascinating."

"I thought the 'MACHOs' and 'WIMPs' was interesting because I have never heard of those for explaining dark matter."

"I found it interesting how all the dark matter 'WIMPs' could have a substantive amount of mass and they don't interact with any light and that they permeate and pass through our galaxy."

"I like that the explanation for the broken spiral arms I saw in the lab is finally revealed."

"I liked the traffic jam analogy. It's interesting to think that stars form that way. And that sometimes they do form, and sometimes they don't."

"The density wave 'traffic jams' in galaxies. I was curious to know more about spiral galaxies."

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

"Nothing really was confusing this week. I'm still scratching my head about our last two weeks' topics (star types and what they 'eat')."

"It was confusing thinking about the size of our galaxy."

"It's kind of difficult for me to imagine the Milky Way being a flattened disc in comparison to our position on Earth. I'm a very visual person and my brain wants to make the Milky Way rounded since we observe it from a rounded planet."

"The idea that we live in a 'flattened disk-shaped galaxy' is confusing because that is hard to visual. I don't see it like a flat disc."

"Dark matter--puzzling over exactly what is is difficult to grasp, as it almost doesn't seem to play by the same rules of physics as the observable world."

"Dark matter. Just like black holes, it's hard to imagine something that can't be seen."

"I don't fully understand how persistence of vision is associated with the Milky Way."

"The PimpStar Rims and traffic jams. I don't really know how to explain how they work."

"I am confused about the PimpStar Rims. Why do people do this to their cars? I truly don't understand."

"I found the PimpStar Rims and everything were confusing; I need more explanation on them."

"I don't really feel confused on anything."

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?

As much as can be seen with the naked eye.	******** [8]
Not very much.	********* [9]
Barely seen it.	*** [3]
(Never been able to see it.)	*** [3]
(Unsure/guessing/lost/help!)	[0]

Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.

1%.	*********** [11]
5%.	[0]
10%.	******* [7]
50%.	* [1]
100%.	* [1]
(Unsure/guessing/lost/help!)	*** [3]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?

"Ask the most honest person around you."

"Use a still pool of water as a mirror."

"Use the back of a spoon."

"Use your phone's camera."

"Just throw my hair in a messy bun that way it looks crazy on purpose."

"If you're really camping, every day is a bad hair day. You will feel the hair sticking out everywhere."

"I always have a bad hair day."

"Look for wild animals, see if they run."

"You can use your hands and feel your hair to find out if your having a bad hair day or not."

"Through your own shadow." "

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.

"Both have LEDs that flash and when put in motion, they appear to create a pattern or seemingly solid color due to blurring."

"They blink and leave an afterimage which is similar to a strobe effect."

"They're electronic lights that spin around the rim of the car and change on an interval that matches how fast the rim is spinning, once the wheel is spinning faster than the human mind is capable of interpreting, the changing colors of lights appear as an image."

"I'm really not too sure. Out of everything taught this was what was most confusing to me in class."

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

"When you say compressed to describe the space where the arms of the galaxy show up, how much is compressed? Or how tightly packed does the matter in these arms need to be in order to generate star formation?" (Just enough to kick-start star formation, which is really hard to start on its own without any help.)

"Is it hard to teach a subject where almost nothing is fact?" (Wait, are you talking about astronomy? At least everything we've covered so far have been verified with evidence. Well, subject to further observations. #keeplooking)

"Can we take a field trip to see the Milky Way (or are there good viewing locations around here?)" (Just make sure the moon is not up. Then go somewhere dark and clear--I would suggest Carrizo Plain, but some other less remote, nearby locations might work.)

"I don't understand how matter isn't being sucked towards the center of the galaxy. If there's a supermassive black hole there, then what is stopping matter from being sucked towards it? I get the 'circling the drain' aspect but wouldn't everything eventually get sucked in?" (In terms of the total amount of stuff in our galaxy, the supermassive black hole is actually quite miniscule. It certainly has cleared out its immediate neighborhood and added it to its mass, but to the rest of everything outside of that vicinity, the amount of gravity from that central region is still the same whether it is a single supermassive black hole, or a cloud of gas, dust and stars. So everything else in the Milky Way goes about its business just the same.)

"Your bike is legit."

"Would you put PimpStar Rims on your car if you got them for free?" (I would add them to the lights on my bike.)

"At what location was your Milky Way picture taken?" (The Atwell Mill Campground in the Mineral King section of Sequoia National Park.)

"What is a telescope you would recommend to invest in for a broke college student?" (For telescopes, most anything you can get from Craigslist that is still functional--no sense buying a telescope new if you're just starting. But also consider binoculars as well.)

"When is our second midterm?" (In two weeks.)

Online reading assignment: the Milky Way (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 Milky Way's shape, size and composition and spiral arm structure and formation.


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.

"That in very dark skies if you take a look at the Milky Way, which to the ancient Greeks resembled a milky stream across the sky."

"I thought the Milky Way night photo was super cool and interesting because it encompasses science and the outdoors in such a beautiful way. I love to be outdoors and in nature so this really resonated with me."

"I like how it was once again proven that we are not the center of the universe as I feel when we think this way without waiting for proof we are very narrow-minded."

"That the Milky Way sort of has arms. Making it look like a spiral."

"The mystery of dark matter is always interesting to hear about. What is dark matter? How can we find it, and once we find it how can we identify it? These are questions I sincerely hope are answered in my lifetime."

"Learning a bit about dark matter in the Milky Way galaxy was interesting. I had no idea that dark matter is what creates and spreads out the gravity in the galaxy. This unusual matter that does not deal with light or stars or gas or dust is holding our galaxy together."

"Dark matter--thinking about the majority of matter that is not seen and doesn't interact with our realm of reality is fascinating."

"Persistence of vision, along with the different examples provided."

"Something interesting was learning about stars' formation. As gas and dust compress, star formation occurs and lights up a spiral arm."

"I liked the traffic jam analogy. It's interesting to think that stars form that way. And that sometimes they do form, and sometimes they don't."

"The PimpStar Rims comparison was a very funny and clever way to compare the formation of the spiral arms in a galaxy. I was able to understand it better."

"I like that the explanation for the broken spiral arms I saw in the GalaxyZoo lab is finally revealed."

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

"I found confusing as to how we can determine the shape of the Milky Way along with where the center is?"

"The fog model."

"The difference between the centered and spread-out mass in a galaxy."

"Dark matter."

"I don't fully understand how persistence of vision is associated with the Milky Way."

"I am confused with dwarf galaxy interactions and the triggering of density waves. I can get that when a smaller galaxy comes close to a bigger one it gets sucked in but I do not understand what it has to do with triggering density waves."

"The entire concept of density waves has gone completely over my head. I dearly hope you'll explain in easier-to-understand terms in class at some point."

"I don't really feel confused on anything."

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?

As much as can be seen with the naked eye.	****** [6]
Not very much.	***** [5]
Barely seen it.	***** [5]
(Never been able to see it.)	****** [6]
(Unsure/guessing/lost/help!)	[0]

Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.

1%.	************ [12]
5%.	** [2]
10%.	**** [4]
50%.	[0]
100%.	* [1]
(Unsure/guessing/lost/help!)	*** [3]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?

"Ask the most honest person around you."

"Use a still pool of water as a mirror."

"Use your phone's camera."

"Just throw my hair in a messy bun that way it looks crazy on purpose."

"If you're really camping, every day is a bad hair day. You will feel the hair sticking out everywhere."

"I always have a bad hair day."

"Look for wild animals, see if they run."

"You can use your hands and feel your hair to find out if your having a bad hair day or not."

"Through your own shadow."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.

"They work because of a series of blinking LED being placed under a rapid speed will emit a certain pattern."

"They blink and leave an afterimage which is similar to a strobe effect."

"It's a set of LED lights that are in the wheels that have a built in microprocessor and adapter. and as they spin it creates the magic."

"I am fairly certain they harness their sheer tastelessness to emit a glow of pure obnoxious energy."

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

"Nearly ten years ago, I went camping with the boy scouts on Catalina Island. When the lights in the camp facilities went off, there was absolutely no light pollution for miles around, so I could see the entire night sky, including the milky way, totally unobstructed for the first time ever. I've always wanted to see the sky that way again, but I haven't been able to find a night sky so clear since then."

"The comic book style notes help."

"Do you imagine the PimpStar Rims or the MonkeyLectric Rims will become popular?" (I have them on my bike.)

"One thing I found confusing is disk stars and halo stars. Which one does our galaxy consists of?" (Both, although the halo star clusters above and below the disk are pretty sparse.)

"I have never gotten a good view of the Milky Way. Where and when in California is the best to view the Milky Way?" (Make sure the moon is not up. Then go somewhere dark and clear--I would suggest Carrizo Plain, but some other less remote, nearby locations might work.)

"What separates galaxies? Void? Void from lack of gravity? Is it safe to assume that space is infinite?" (The space between galaxies really is empty (no gas/dust, so no stars will ever be made in that space). Right now it seems that the universe is infinite, or at the least so large that it might as well be infinite, but that's not a completely settled question.)

"When is our second midterm?" (In two weeks.)

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: 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."

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]

Astronomy quiz archive: stellar evolution

Astronomy 210 Quiz 6, spring semester 2019
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz06nD4d


Section 30674

0- 8.0 :
8.5-16.0 :	**** [low = 9.0]
16.5-24.0 :	************
24.5-32.0 :	******* [mean = 24.7 +/- 7.9]
32.5-40.0 :	******** [high = 40.0]

Section 30676, version 1
Exam code: quiz06s33N


Section 30676

0- 8.0 :	* [low = 7.5]
8.5-16.0 :	*****
16.5-24.0 :	************** [mean = 23.5 +/- 6.5]
24.5-32.0 :	*****************
32.5-40.0 :	**** [high = 36.5]

Online reading assignment: the Milky Way (SLO campus)

Astronomy 210, spring 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 Milky Way's shape, size and composition and spiral arm structure and formation.


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 really liked learning about the Milky Way because when I was young and went to LA you couldn't see the Milky Way, but at home you could see it really nicely without the light pollution. Learning about dark matter was crazy as well because I didn't know a lot about it."

"I really liked learning about the Milky Way. I live out in the country so on super clear night growing up as a kid I was able to see the Milky Way."

"That the word 'galaxy' derives from the Greek word for milk, interesting fact."

"The fog model. The idea that there are things we can't see because of things being in the way is fascinating."

"How big the Milky Way is."

"I thought the bad hair day camping was a funny and interesting analogy."

"I guess I never really thought about how we would image our own galaxy, looking from the inside out. But the way that we do it is pretty interesting. It's confusing, but I'm sure the lecture will clear it up."

"That we actually have a method to determine our galaxy to be a spiral galaxy and it's not just assumption."

"I never thought about how hard it would be to figure out what size and shape our own galaxy is since we are inside of it and have no mirror for reference."

"Learning about the Milky Way and its spiral arms was pretty interesting. I liked it because the Milky Way is always talked about, but never in this much depth."

"That people were able to come up with ways to picture our own galaxy even though it's huge and we can barely get to other planets at this point."

"That we can use the orbital motion of the sun to find the mass of the galaxy inside the sun's orbit. The fact we're able to infer this correlation blows my mind. It makes total sense, too. Plus, even if it's not exact, the fact that we can even get an estimate also demonstrates just how interconnected everything really is. We've been able to learn so much about space already, even with the extremely limited data we actually have."

"Dark matter because the idea of unexplained and mysterious phenomena are always intriguing and exciting."

"I thought that the idea of dark matter was super-weird and interesting. But it does make a lot of sense."

"Dark matter is cool because is it scary and most of the universe is dark matter. Creepy."

"How we detected the spiral arm 'lanes' of the Milky Way, because they don't just use a regular telescope."

"The wildfire analogy for star births through type II supernova explosions was interesting. I find it helpful to have comparisons to more common everyday occurences that I have actual experience dealing with when trying to understand the abstract astronomy subjects."

"The formation of the Milky Way is based on a lot of theory, and that some of the mathematical estimations could be as much as 10% off. It's interesting to know that there is still much knowledge to discover."

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

"Why can we see the Milky Way but we are a part of it."

"I'm still not totally sure about how we can use things like globular clusters to find the size and center of the galaxy, but after reading the textbook on the various ways we figured it out, that was cleared up more for me. I'm not really confused on anything else in this section."

"The globular cluster part about the Milky Way was a bit confusing. The image that was provided didn't make much sense to me--I just think I need a better, in class explanation."

"The period-luminosity relation."

"I want to know more about dark matter. What are your ideas of what it could possibly be made of?"

"Dark matter, I've always heard of the references to what darkmatter is and how its a major part of our universe, but the MACHOs and WIMPs categories still confuse me on the subject still."

"WIMPs--what is a weakly interacting massive particle? How can something be weakly interacting?"

"Star formation in spiral arms."

"How density waves work."

"The spiral arm/Pimpstar Rim optical illusion thing. I get it on a basic level, but I need more explanation."

"The spiral arms, I didn't really understand the concept of them."

"Self-sustaining star formation--why is it prominent in some galaxies and not all?"

"I think I'd just like more in class discussion on all the presentation slides."

"Just about everything I have read."

"Pretty straightforward slides!"

"It all clicked."

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?

As much as can be seen with the naked eye.	********* [9]
Not very much.	*************** [15]
Barely seen it.	*** [3]
(Never been able to see it.)	***** [5]
(Unsure/guessing/lost/help!)	[0]

Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.

1%.	************ [12]
5%.	***** [5]
10%.	********* [9]
50%.	** [2]
100%.	[0]
(Unsure/guessing/lost/help!)	**** [4]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?

"Look in the reflection of a pond/river/lake."

"Check in the reflection of the water? Honestly, I'd have a hat though."

"If a car is nearby look in the window."

"Take a selfie."

"Ask your fellow campers or study their reactions to you when you climb out of your tent."

"Ask a friend you trust who has a verifiable history of qualifying good and bad hair days in accordance with your hair day system of values."

"Ask a wild animal."

"Ask a grizzly bear."

"I don't usually care about what I look like when I'm camping."

"Camping hair don't care."

"Probably just roll around in the dirt. Then I'll know for sure that I’m having a bad hair day, and there won't be any mystery anymore."

"Make sure your camping partners look worse than you so no one can tell you're ugly."

"Look at your shadow."

"I would use my hands to feel, if my hair is in place relative to my head."

"I would just run my fingers through it, the more knots the more painful the hair looks."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.

"Rapidly blinking lights are coordinated to create patterns when swept across our field of vision."

"For Pimpstar Rims there is a microprocessor in each wheel and images are sent to each wheel through wirelessly. For MonkeyLectric, there are many different designs that are already picked out that were created by different artists."

"Using LED lights set into the rims of cars or bikes the lights are able to make a picture as the wheel spins. The article said they use 'strobe modulation effect' kind of like a marquee where the lights light up and make it appear as if the words are moving in fluid motion instead of lights just lighting up."

"Usually one 'spoke' made up of a handful of LEDs spin around fast enough to create what appears to be a solid disk. By changing the LEDs at a rate that correlates to the spinning speed, it can create a picture."

"I think the reason that they work is because the light on the wheels when going really fast make it seem that there's a solid color, similar to when you turn on the fan and the blades when going fast look like a single big blade. How they create the cool patterns I'm not sure."

"PimpStar Rims are rims on a car made to put a design/ make a visual illusion to people that drive by. The spiral arms of the Milky Way are a similar persistence of vision illusion--like the lights on Pimpstar rims, short-lived massive stars are born and die at certain intervals as they orbit around. MonkeyLectric Rims are the same but for bikes."

"The wheels have freaking pictures!"

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

"If you could elaborate on the shape of our galaxy in class, please?"

"I'm a bit confused as to why the Milky Way galaxy is flat disk shaped. In the globular cluster positions slide, it shows the star clusters above and below the disk but there's still clusters inside the blue disk right? Where is the border where star clusters are officially part of the Milky Way and where they're not?" (Yes, the globular clusters are everywhere in the halo (above and below the disk), and also can pass through the disk as they circle around their tilted orbits.)

"Why is it called 'dark' matter when it is actually made up of light matter?" (We can't see dark matter (yet)--it doesn't give off light (like stars, or emission nebulae), doesn't reflect light (like fine dust), and it doesn't even block light (like clumpy dust particles). Perhaps a better term for dark matter is "non-light interacting matter.")

"Why did you want us to look at the ugly rims?"

"The LED lights for your bike are really cool and nicely personalized."

"I must be a child because I laughed at 'Pimpstar.'"

"Is it true that there are more stars in universe than grains of sand?" (If the universe is infinite, and each star in this infinite universe has a planet with sandy beaches, then probably so. #mindblown)

"How do you feel about 'Song About The Sun' by They Might Be Giants?" (Eh. It's okay.)

"We should do a potluck!" (We'll do a "knowledge potluck" for the final exam. Just make sure you at least bring enough for yourself.)

"Do you like camping? Do you consider yourself to be high-maintenance?" (Yes, and probably yes. I usually just wear a hat when backpacking, though. #doitforthegram)

"What was your Ph.D. research on? Why'd you choose that?" (Atomic holography. Because, holograms. Of atoms.)