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

Astronomy 210, spring semester 2017
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 found learning about the fusion process to be very interesting, as it helps me get a better understanding of how stars develop and live their life."

"I understand why the sky appears to be blue. I have vindication for child me arguing about the color of the sky (literally)."

"I found the different colors connected to the different nebulaes very interesting, as well as their amounts of particles/lack of."

"It was interesting to look at the different nebula and see the colors that the human eye perceives."

"The colors and shapes of the nebulae, they were really beautiful and interesting."

"I thought the house party model was pretty cool. Totally relatable and made it easy to remember the differences between the star masses and the length of time they 'live.'"

"I found it interesting that a white dwarf is denser then a giant star. I though the bigger the denser, but I guess not when it comes to stars."

"It's crazy that the mass of white dwarfs is so dense that one teaspoon of it would weigh 15 tons on Earth."

"Cold fusion was an interesting topic because of how it isn't possible."

"How you used the cheerleader model to explain how fusion works in a star."

"Interstellar reddening giving the color to things such as the sunset. I didn't think the atmosphere provided a filter to change the glow of the sun and stars."

"That star cluster stars are all born at the same time but age differently because its interesting that they are in a sense like us with people we are the same age as and but we all age differently."

"That average stars spend 90% of its life on the main sequence."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I find fusion to be very confusing, as there are many terms in the description of this process that I have forgotten or have become 'fuzzy' on."

"Nebulae, in general."

"It was hard to tell when the stars were coming or going on the main sequence line. Because most were on the right side where they could either be coming or going."

"I'm pretty confident that I understand the material covered in these sections. I'm sure I'll be able to concoct a question in class though. Usually once I hear other students' ideas it sparks questions!"

"The proton-proton chain, was confusing to me just understanding the terminology."

"The house party model--I was struggling to understand the turn-off points and main sequence line."

"How you can tell which star has the best fusion rate."

"Star clusters and how they explain stellar evolution."

"All of the star cluster age information--the H-R diagram didn't resonate with me and the turn-off point didn't make sense."

Rank the luminosities of these main-sequence stars (1 = brightest, 3 = dimmest). (There are no ties.)
(Only correct responses shown.)
Massive: brightest luminosity [95%]
Medium-mass (sunlike): medium luminosity [95%]
Low mass (red dwarf): dimmest luminosity [100%]

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 [75%]
Medium-mass (sunlike): medium fusion rate [100%]
Low mass (red dwarf): slowest fusion rate [75%]

Fusion requires high temperatures in order for nuclei to move quickly enough to:
break heavy elements apart.  ** [2]
create convection currents.  * [1]
overcome gravity.  * [1]
overcome repulsion.  ************** [14]
(Unsure/guessing/lost/help!)  ** [2]

Briefly explain why "cold fusion" (producing energy from hydrogen fusion at room temperature) would be implausible.
"Would be implausible due to the fact that heat is needed for any sort of fusion."

"Because fusion requires high temperatures. So if there is low pressure and low temperature, then there fusion would be low or not at all."

"The atoms are not moving fast enough to get through repulsion, so they would not collide or fuse."

"Cold fusion' is implausible, because in order for fusion to occur, the hydrogen atoms have to be squeezed a lot and moving very quickly. If the temperature isn't high enough then the hydrogen atoms won't move fast enough to fuse together."

"A hydrogen nucleus is just a proton so both would be positively charged and like charges repel."

Match the three different types of nebulae with their colors.
(Only correct responses shown.)
Emission: pink [90%]
Reflection: blue [90%]
Dark: brown/black [100%]

Match the three different types of nebulae with their composition.
(Only correct responses shown.)
Emission: hydrogen [95%]
Reflection: small dust particles [100%]
Dark: large dust particles [95%]

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 [70%]
Medium-mass (sunlike): medium main-sequence lifetime [90%]
Low mass (red dwarf): longest main-sequence lifetime [75%]

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.  ************** [14]
After most everyone has left.  * [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Living on Earth might be expensive but at least you get a free trip around the sun every year."

"How long does it typically take for dust clusters to turn into stars whether kickstarted or regular pace?" (If not kickstarted by a nearby supernova, then it takes less than a million years for a molecular cloud to collapse into a massive star (because there's more gravity); or 10 million years or more for lower mass stars (with less gravity to gather up material.)

"Since there is a pattern for the main sequence stars (mass proportional to luminosity), what relationships (if any) apply for the 'other stars?'" (All the main-sequence stars are fusing hydrogen, so all their luminosities are related to their masses. However, all the "other stars" are dying or dead stars, having already used up all their available hydrogen, so their luminosities are either produced by stop-gap energy sources, or whatever energy is leftover after no more is produced--that's why all their luminosity values are all over the place compared to their masses.)

"Are you planning on throwing a house party, and are we invited?" (There is no actual house party. ಠ_ಠ)

"I show up early to a house party of a good friend."

"You know, seeing as I'm not super-hella social, I honestly probably wouldn't go to a house party. If I were to go to one, I would probably go between the 'on-time' and 'once people are already there,' but at the same time I would probably leave sooner rather than later..."

"Do we need to know the speed of the the massive, medium mass, and low mass star evolution tracks on an H-R diagram?" (Yes, that's part of the house party model.)

"I think it would be good if we could have more of a comprehensive or specific study guide for the next midterm. You said that it would be more technical because we are dealing with some harder topics, so a study guide could really help direct us to what we should specifically study."

"The reading explained that eventually the sun would increase in luminosity and destroy Earth; is there evidence of this happened to other planets?" (Yes, the red giant BD+48 740 contains lots of lithium, which is not produced in stars, and is easily broken down by star's high temperature, but is abundant in terrestrial planets--this is interpreted as evidence that BD+48 740 swallowed up at least one of its inner planets as it expanded into a red giant.)

"Can fission happen with lighter atoms? Why just heavy atoms like uranium--is it unstable and thus easier to break down? It's confusing because I can't find the answer without reading a hella-long webpage written for people who already understand it." (Uranium and other heavy atoms have lots of protons, which all repel each other, and are easier to break apart if they don't have just the right amount of neutrons to help them "stick" to each other. Since lighter atoms they have fewer protons and less repulsion, they're not as likely to fall apart unless they have a very unfavorable amount of neutrons to stick everything together.)

"How do you assign the seating charts? Is it completely random or do you keep certain people with certain people?" (I tend to keep people that are equally as smart as each other from being in the same group, in order to make each group a good "mixture" of students.)

I'm a little confused about brown dwarfs. Are they actually stars?" (They're just "failed" stars, because they don't have enough pressure in the cores to start hydrogen fusion. They're less massive than red dwarfs, which have just enough mass to create pressure in their cores to have hydrogen fusion.)

"I really appreciate the blog presentations. I find those much more understandable than reading out of the book."

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