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

Astronomy 210, spring semester 2015
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.

"Reflection nebula--I like the way the red light wiggles through the dust cloud and the blue light scatters."

"Star life cycles--they say a million years is a short life, yet seems like a really long time for us."

"The house party model. Probably the most interesting real world example I've been given."

"Star clusters and nebulas because the pictures are really cool."

"We can measure and say all these things about stars without ever physically viewing and directly measuring them."

"That there are only three real colors in the background of space means there is a lot of fake pics."

"I found it interesting that you were able to compare fusion with cheerleaders--well played, P-dog."

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

"Astronomy is confusing."

"I understand the material, it's just I don't feel like the information we've read on the evolution of stars is enough proof to to sell me these 'processes' on how to label the ages of stars and galaxies. I feel like its just a bunch of guessing. But, hey, I get that this is only an introduction to astronomy, and frankly I'm too lazy to do the math to back up these theories--so I'll just shut up and roll with it."

"I found tha H-R diagram to be confusing. I get confused when trying to read it and how to read the O B A F G K M letters at the top."

"Confused on fusion rates compared to different stars?"

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 [100%]
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 [66%]
Medium-mass (sunlike): medium fusion rate [93%]
Low mass (red dwarf): slowest fusion rate [69%]

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

break heavy elements apart.	*** [3]
create convection currents.	**** [4]
overcome gravity.	***** [5]
overcome repulsion.	********** [10]
(Unsure/guessing/lost/help!)	******* [7]

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

"The protons do not warm up enough to move fast enough to be able to "bump" in to each other."

"Because heat is needed to get atoms moving fast enough to smash into each and create energy."

"It would be implausible because for fusion to occur the temperature would need to be high as well as the pressure needing to be high."

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

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

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

Emission: hydrogen [76%]
Reflection: small dust particles [83%]
Dark: large dust particles [66%]

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 [69%]
Medium-mass (sunlike): medium main-sequence lifetime [83%]
Low mass (red dwarf): longest main-sequence lifetime [69%]

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

Early, or on time.	****** [6]
When the most people should be there.	********************* [21]
After most everyone has left.	** [2]

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

"Is the second midterm cumulative of the semester so far, or just the material after the first midterm?" (Just the material after the first midterm, so Quizzes 4-6 only.)

"What are you going to do for spring break?" ("The mountains are calling, and I must go.")

"Is it bad that for once I actually don't have a comment?" (I would think that counts as a comment.)

"When do you show up to a house party? And you can bring Mrs. P-dog if she wants to come!" (We're always late, but worth the wait.)

Online reading assignment: advanced electricity

Physics 205B, spring semester 2015
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 reviewing presentations on circuit analysis and previewing presentations on advanced electricity concepts.


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.

"I understand that a ammeter measures the current passing through a light bulb while a voltmeter measures the amount of potential used by a light bulb."

"I understood the difference between parallel and series circuits and how to calculate problems using their equations. I also learned to reset your circuit breaker you have to unplug your appliances which is good to know in order to complete a circuit."

"Ammeters have zero resistances, and voltmeters have infinite resistances."

"Current and potential difference in a circuit can be measured with instruments called ammeters and voltmeters, respectively. A multimeter functions as an ammeter or a voltmeter, depending on the setting of a switch and which of its terminals are connected."

"When more appliances are plugged in to an outlet, the resistance will decrease (when can be very dangerous). In addition, we have circuit breakers to prevent current levels from reaching a dangerously high level--if the circuit breaker is triggered, this turns off the electricity so that the wires in the house do not become fried."

"When equivalent resistors are placed in series, the resistors have an additive effect. However, when equivalent resistors are placed in parallel of each other, then the total resistance is the sum of the reciprocals of the resistors added together."

"When you plug in more and more space heaters at your house, the resistance becomes lower and lower. This can become dangerous because it means that the current can flow higher and higher."

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 don't understand anything else regarding ammeters and voltmeters. I'm also unsure how to work with equations using R_eq and current I."

"I dont understand anything with ammeters or voltmeter except one is close to zero and one is close to infinity?"

"I found ammeters and voltmeters to be confusing. I also found combination so series and parallel resistors to be confusing."

"All this electrical stuff is very confusing to me and a bit uninteresting."

"I was confused as to why a circuit would have to be broken open if connected to a ammeter. Also was confused as to what power dissipation is."

"Ohm's law parameters. It's just a very new 'language' to me. So trying to understand exactly how they really work together is weird."

"For some reason the connection between I and ∆V is still unclear."

"Lots of equations, not sure when to use which. I think I understand how the different terms can be substituted to relate some of the equations to each other, but the applications of the equations are a little confusing."

What are the resistances of these (ideal) devices?
(Only correct responses shown.)

Ideal ammeter: 0 [71%]
Ideal voltmeter: ∞ [63%]

Determine what will happen to the following parameters when additional electrical appliances are plugged in and turned on in the same household circuit.
(Only correct responses shown.)

Equivalent resistance R_eq of circuit: decreases [49%]
Current I flowing through emf source: increases [41%]

A fuse or circuit breaker is designed to prevent too much __________ in household wiring.

current.	******************************* [31]
voltage.	**** [4]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	*** [3]

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

"Felt pretty great about the midterm. Did a little better than last semester's midterm."

"I am kind of lost here and would benefit from a lot more help in class."

"Just so I have this straight. A voltmeter and ammeter are the same instrument but when the wiring of a circuit is open and we are measuring the current the voltmeter becomes an ammeter?" (Yes, but don't forget to change the dial settings on the multimeter to tell it to change from a voltmeter to an ammeter.)

"Are you ready for spring break, yet?" ("The mountains are calling, and I must go.")

"Welding circuits typically range from 70-200 amps. Dangerous stuff is so fun."

Physics midterm question: total internal reflection at fluorite-water interface?

Physics 205B Midterm 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 23.78

Light in fluorite (index of refraction of 1.39) is incident at an ethyl alcohol interface (index of refraction of 1.36), and this light is totally internally reflected back down into fluorite. (Drawing is not to scale.) Then the ethyl alcohol is replaced with a layer of water (index of refraction of 1.33) poured onto the fluorite. Discuss whether or not total internal reflection also occurs at the fluorite-water interface, if the angle in fluorite is the same as before. Explain your reasoning using the properties of light and refraction.

Solution and grading rubric:

• p:
  Correct. Discusses/demonstrates:
  1. because the critical angle for fluorite up into ethyl alcohol is 78.1°, the incident angle in fluorite must be greater than 78.1° for total internal reflection to occur at the fluorite-ethyl alcohol interface;
  2. with this same angle in fluorite (any value at or greater than 78.1°), this is larger than the critical angle for fluorite up into water (73.1°), such that total internal reflection also occurs at the fluorite-ethyl alcohol interface. (May instead put any angle at or greater than 78.1° as the incident angle in fluorite in Snell's law to find that the transmitted angle in water is undefined, and interprets this as total internal reflection occurring at the fluorite-water interface.)
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Typically solves for the two critical angles, but either does not sufficiently explain total internal reflection for the fluorite-water interface, or explains that total internal reflection will not occur.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete. Some attempt at solving for the critical angles, but switches the incident and transmitted indices of refraction (resulting in an calculator error), or because the incident and transmitted indices are switched, discusses how total internal reflection will not occur.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying Snell's law and/or critical angles.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Approach other than that of applying Snell's law and/or critical angles.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01p34K
p: 24 students
r: 7 students
t: 11 students
v: 4 students
x: 1 student
y: 0 students
z: 0 student

A sample "p" response (from student 0203):
Another sample "p" response (from student 1828):
A sample "t" response (from student 0550):

Physics midterm question: microscope object distance and barrel length

Physics 205B Midterm 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 24.37

A microscope has a "barrel length" (distance from lens-to-lens) of 20 cm when an object is placed at a certain distance in front of the objective lens. Discuss why the barrel length of the microscope must increase if the object distance in front of the object lens is decreased. Explain your reasoning by using a ray tracing and/or thin lens equations, the properties of lenses, images, and magnification.

Solution and grading rubric:

• p:
  Correct. Discusses/demonstrates:
  1. the objective takes an object in front of it (outside of its focal point), and makes a real image behind it;
  2. the location of the real image produced by the objective determines the placement of the focal point of the eyepiece, which sets the barrel length of the microscope (between the inside focal lengths);
  3. thus from the thin lens equation decreasing the object distance (while d_o1 is still greater than f) will increase d_i1, which then must increase the barrel length of the microscope.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Typically discusses (1) and (3), but does not explicitly show (2) how the placement of the eyepiece must be moved back, which increases the barrel length.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete. Has only one of the three points in (p).
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying applying properties of lenses, images, and angular magnification.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Approach other than that of applying properties of lenses, images, and angular magnification.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01p34K
p: 17 students
r: 4 students
t: 4 students
v: 11 students
x: 1 student
y: 0 students
z: 0 student

A sample "p" response (from student 8518):

Physics midterm question: interference of out-of-phase radio transmitters

Physics 205B Midterm 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Example 25.1, Problem 25.1

Two vertical radio transmitters broadcast at the same wavelength of 1.2 m, and are spaced 4.8 m apart along the east-west direction. A receiver held by a Physics 205B student located to the east of both transmitters detects a destructive interference signal. Discuss whether a receiver held by another Physics 205B student located to the south will detect a constructive, destructive, or something in-between a constructive and destructive signal. Explain your reasoning using the properties of source phases, path lengths, and interference.

Solution and grading rubric:

• p:
  Correct. Discusses/demonstrates:
  1. that the radio transmitters are out of phase, as the difference in path lengths to the student located to the east is four times the wavelength, which would be constructive interference for in phase sources, but destructive interference (as is the case here) for out of phase sources;
  2. there is zero difference in path lengths to the student located to the south, which means that the out of phase sources will interfere destructively in that direction as well.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. At least discusses how (1) transmitters are out of phase, but does not sufficiently explain (2) the destructive interference for the south receiver.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete. Only (1) or (2) is complete, typically understands that difference in path lengths to the south receiver is zero.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at discussing source phases, path lengths, and interference.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Approach other than that of discussing source phases, path lengths, and interference.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01p34K
p: 20 students
r: 7 students
t: 13 students
v: 7 students
x: 0 student
y: 0 students
z: 0 student

A sample "p" response (from student 5425):
A sample "t" response (from student 1107):

Physics midterm question: comparing total electric field magnitudes

Physics 205B Midterm 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 16.15

Two point charges are held at fixed locations. A +8 nC charge is at the origin, and a second –4 nC charge is at x = +2 cm. The electric field at x = +4 cm is measured. The charge at the origin is then changed to +4 nC, and the electric field at x = +4 cm is again measured. Discuss why the second case has a greater electric field magnitude at x = +4 cm. Explain your reasoning using properties of electric forces, fields, and vector superposition.

Solution and grading rubric:

• p:
  Correct. Discusses/demonstrates that the (total) electric field at x = +4 cm would be greater for the second case (B) using the superposition of the electric field vectors from both source charges (Q₁ = +8 nC and Q₂ = –4 nC for case (A); Q₁ = +4 nC and Q₂ = –4 nC for case (B)), which in both cases point in opposite directions, such that superposition of these vectors is the difference of their magnitudes, and either:
  1. explicitly evaluates the numerical values of the total electric field at x = +4 cm to show that it is indeed greater for the second case (B);
  2. qualitatively discusses how the electric field produced by the Q₁ source charge always points in the opposite direction of, and has a magnitude less than the electric field produced by the Q₂ source charge, such that decreasing the amount of the Q₁ source charge (while keeping its (–) sign) will decrease the amount "subtracted" from the electric field produced by the Q₂ source charge.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. May have a minor computational error, but at least conclusion is consistent with result.
• t:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Nearly correct, but argument has conceptual errors, or is incomplete. At least some attempt at evaluating electric fields created by each source charge at x = +4 cm and vector superposition.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Focus on comparing force exerted by source charge Q₁ on source charge Q₂, instead of the comparing effect of electric fields created by source charge Q₁ and source charge Q₂ on x = +4 cm.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Approach other than that of applying electric forces, fields, and vector superposition.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01p34K
p: 30 students
r: 1 student
t: 3 students
v: 12 students
x: 0 student
y: 0 students
z: 0 student

A sample "p" response (from student 1828):
Another sample "p" response (from student 8984):
A sample "v" response (from student 0203):
A sample "y" response (from student 1212):

Physics midterm problem: object distance with greatest magnification

Physics 205B Midterm 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 23.63

An object can be placed either 16 cm or 14 cm in front of a f = +15 cm converging lens. Decide which object distance will result in the largest image (regardless of being real/virtual, or inverted/upright), or if there will be a tie. Show your work and explain your reasoning using the properties of lenses, thin lens equations and/or ray tracings.

Solution and grading rubric:

• p:
  Correct. Compares the linear magnification ratios of both object distances using one of two methods:
  1. determines the image distances produced by these objects, then sets up the ratio m = –d_i/d_o to find their respective linear magnification factors;
  2. a carefully, properly scaled ray tracing diagram.
• r:
  Nearly correct, but includes minor math errors. May have sign errors or inverse errors.
• t:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. At least enough steps are shown that would theoretically result in a complete answer, multiple errors (or omission of last step of finding m = –d_i/d_o ratio) notwithstanding. May draw a ray tracing diagram that does not have its object distances properly scaled with regards to the focal points, but at least makes a consistent conclusion based on the faulty scaling of object positions.
• v:
  Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Ray tracings have real images for both cases, etc.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01p34K
p: 21 students
r: 6 students
t: 13 students
v: 6 students
x: 1 student
y: 0 students
z: 0 student

A sample "p" response (from student 8984):

Astronomy current events question: Chang'e 3 probe of underground lunar lava layers

Astronomy 210L, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Kelly Beatty, "Lots of Lunar Layers Under Chang’e 3" (March 13, 2015)
http://www.skyandtelescope.com/astronomy-news/change-3-lunar-layers-031320154/

The Chinese National Space Administration moon rover Yutu studied underground lava flow layers using:
(A) chemical ablation lasers.
(B) ground-penetrating radar.
(C) a remote digger.
(D) infrared cameras.
(E) GPS triangulation.

Correct answer: (B)

Student responses
Sections 30678, 30679, 30680
(A) : 3 students
(B) : 22 students
(C) : 1 student
(D) : 8 students
(E) : 1 student

Astronomy current events question: NASA's Asteroid Data Hunter challenge awards

Astronomy 210L, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Sarah Ramsey, "New Desktop Application Has Potential to Increase Asteroid Detection, Now Available to Public" (March 15, 2015)
http://www.nasa.gov/press/2015/march/new-desktop-application-has-potential-to-increase-asteroid-detection-now-available/

NASA's Asteroid Data Hunter challenge awarded participants for __________ to search for near-Earth asteroids and comets.
(A) developing software algorithms.
(B) scanning photographic plates.
(C) hosting automated telescopes.
(D) repurposing satellite TV dishes.
(E) using smartphone apps.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 21 students
(B) : 7 students
(C) : 3 students
(D) : 2 students
(E) : 2 students

Astronomy current events question: Enceladus' hydrothermal vents

Astronomy 210L, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Dwayne Brown and Preston Dyches, "Spacecraft Data Suggest Saturn Moon's Ocean May Harbor Hydrothermal Activity" (March 11, 2015)
https://www.nasa.gov/press/2015/march/spacecraft-data-suggest-saturn-moons-ocean-may-harbor-hydrothermal-activity/

__________ detected by NASA's Cassini spacecraft provide evidence of active hydrothermal vents on Enceladus, Saturn's moon.
(A) Infrared emissions.
(B) Sulfur plumes.
(C) Magnetic field fluctuations.
(D) Moonquakes.
(E) Microscope rock grains.

Correct answer: (E)

Student responses
Sections 30678, 30679, 30680
(A) : 7 students
(B) : 7 students
(C) : 5 students
(D) : 1 student
(E) : 15 students

Online reading assignment question: helpful/unhelpful physics midterm study tips

Physics 205B, spring semester 2015
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.

Describe something notable that either helped or did not help with studying for this midterm. Selected comments may be discussed in class. (Graded for completion.)

The following are all of the student responses to this question, verbatim and unedited.

"Doing practice problems over and over again.”

"I do not know what some letters are standing for."

"Going over the past midterm questions with the explanations helps clarify concepts."

"procrastinating does not help. studying helps heeps."

"Practice problems always help me when I'm studying."

"The general review questions posted for the midterm was helpful. The in class review was also helpful in clarifying my issues with the electric forces question."

"I still think that the fact that you post the questions we need to focus on is really helpful"

"What helps me to study for this midterm is youtube."

"The only thing that helps me study is to do lots and lots of practice problems. The questions on the blog are great for review as well as the blog itself. I also like to review quizzes, class notes, and do the worksheet questions for each unit."

"Reading over the online material and doing the practice problems."

"Sometimes I wish we could have had some verbal explanations/notes to write down with our worked out problems to understand why we are going through the steps. I think think this would make studying our notes much more productive. I spend more of my time looking at the notes and wondering what we are even doing."

"Review notes from class as well as the blog for the midterm."

"I tell you what. Studying for physics is one of hardest subjects for me. I've tried so many different methods. Most other subjects (exception of chemistry. I put chemistry and physics almost of the same pedestal of hardness) I can figure out a solid good way to study, but for physics I am still kind of figuring it out. But what seems to work best for me so far is doing as many problems as possible. It helps me to do the same problem over twice. The second time through I try to 'test speed' because on exams it like we have to rush on our exams and not take our time. So the first time on a problem I go slow and really try to explain logically why it all works, then the second time through the problem I try to go faster. Having a really good answer key is very helpful. Otherwise I don't know if I'm doing the problem right. I want to see the explanations as much as the answers. Trying to do all the variations a problem can be presented helps, too. Bottom line, I find that you can't just read your notes or the book. You have to actually work out problems."

"the blog"

"It helps to look at all the past quiz and midterm questions."

"Taking short breaks in between studying helps a lot and writing notes down to help organize topics."

"Just going over the narrowed list of things that could be on it...rather than trying to cram everything."

"The practice questions assigned from previous midterms really help me study for the midterm. I find taking the subjects covered in the questions and reworking them to study every way the question could be asked, really helps me fully understand the subjects, and helps to be prepared for anything I am asked."

"Knowing how the equations work with each other, how they are either inversely proportional too each other or changes the outcome of other equations."

"I really like the examples given for the study guide because it does a good job of letting me know what I really need to focus on in order to do well on this midterm."

"Something that helps me is setting a timer for 25 min. I tell myself I can't get up or let my mind wander for 25 min. Then for five min I can take a break: go to the bathroom, get a snack, check facebook, do pushups. Then another 25 min of good concentration."

"Something that really helps me is all the practice problems you post. Since the problems in the book just confuse me your samples are the best way to go."

"Tutors help clarify things."

"Reviewing old quizzes and midterms are immensely helpful, as they give me a rough idea of what topics will be covered, and what areas I need to work on."

"looking at problems is not enough. They have to be worked out."

"Khan academy is helping me out. They dumb it down for me to understand the basics."

"I found that printing out the Quiz Flashcard questions prior to lecture helps immensely. I work on them along the way as we cover the topics in class, and then I use them as a study guide for the exam."

" More midterm- like questions should be practiced in class rather than just multiple choice. Free response questions require a completely different studying pattern than multiple choice."

"Going through all of the blogs to refresh, then working on practice problems, and getting all the equations down."

"Having the practice questions help."

"Have some examples to pratice will be very helpful."

"Posted example problems on waiferx helped out big time."

"Work every problem out until you can successfully do it without looking at the answer. Then do it 3 more times."

"helpful: the posted midterm from last year. Now i feel like i have a better grasp at how the exam will be set up."

Astronomy quiz archive: solar system

Astronomy 210 Quiz 4, spring semester 2015
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz04NoR3


Section 30674

0- 8.0 :
8.5-16.0 :	******* [low = 12.0]
16.5-24.0 :	*************** [mean = 23.5 +/- 6.6]
24.5-32.0 :	***********
32.5-40.0 :	***** [high = 36.5]

Section 30676, version 1
Exam code: quiz04s0U7


Section 30676

0- 8.0 :	* [low = 8.0]
8.5-16.0 :	**********
16.5-24.0 :	************** [mean = 24.4 +/- 8.6]
24.5-32.0 :	************
32.5-40.0 :	********** [high = 40.0]

Online reading assignment: stellar parameters (SLO campus)

Astronomy 210, spring semester 2015
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 parallax, distance, apparent magnitude, absolute magnitude, Wien's law and the Stefan-Boltzmann law.


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 blue stars are hot and red stars are cold. You would think it would be the other way around"

"I knew there were different colored stars but I didn't realize that white stars are cooler than blue stars. I was going off of flame hotness."

"I like the way astronomers measure luminosity how they 'level the playing field' in a way by taking the stars in comparison and placing them equal distances away and not just going off of the apparent brightness from Earth. This is interesting to me because it make one have to step back and remember that all that is seen from Earth is not all reality and we are much smaller than we presume ourselves to be."

"This chapter wasn't particularly interesting. Or it isn't yet because its too hard to understand and so it makes me mad and not interested at all. wtf"

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

"I was a bit confused about how to determine size of a star even with the other data known."

"I am very confusing about what the heck parsecs are."

"I am not totally familiar with the Hertzprung-Russell diagram. This is my first time ever hearing about it."

"wtf is going on in this chapter. I thought we were at a community college, not Harvard. I like this class a lot and was going to major in astrophysics but not I'm having second thoughts."

Explain how apparent magnitude and the absolute magnitude are defined differently.

How bright a star or any other celestial body looks in space is measured by something called apparent magnitude. The absolute magnitude of an object, such as a star, equals how bright that object would look if it were 10 parsecs, or 32.6 light years away from Earth."

"Apparent magnitude is what you 'think' you see. Absolute is the 'scientific' seeing."

Suppose the sun was moved to a distance of 10 parsecs away. As a result, its __________ magnitude would become dimmer.

absolute.	************* [13]
apparent.	************************ [24]
(Both of the above choices.)	** [2]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	* [1]

Rank the brightnesses of these stars (1 = brightest, 4 = dimmest; there are no ties), as seen from Earth.
(Only correct responses shown.)

1 (brightest): the sun, m = -27 [90%]
2: Canopus, m = –1 [78%]
3: Vega, m = 0 [85%]
4 (dimmest): Kapteyn's star, m = +9 [88%]

Rank the brightnesses of these stars (1 = brightest, 4 = dimmest; there are no ties), if relocated to 10 parsecs from Earth.
(Only correct responses shown.)

1 (brightest): Canopus, M = -3 [68%]
2: Vega, M = +0.5 [70%]
3: the sun, M = +5 [65%]
4 (dimmest): Kapteyn's star, M = +11 [78%]

Determine the stars that get dimmer or brighter when relocated from their original positions to 10 parsecs from Earth.
(Only correct responses shown.)

The sun: gets dimmer [78%]
Canopus: gets brighter [64%]
Vega: gets dimmer [58%]
Kapteyn's star: gets dimmer [52%]

Rank the temperatures of these main sequence stars (1 = hottest, 4 = coolest; there are no ties).
(Only correct responses shown.)

Hottest: blue main sequence star [75%]
Second hottest: white main sequence star [60%]
Third hottest: yellow main sequence star [63%]
Coolest: red main sequence star [78%]

Rank the temperatures of these supergiant and dwarf stars (1 = hottest, 4 = coolest; there are no ties).
(Only correct responses shown.)

Hottest: blue supergiant [70%]
Second hottest: white dwarf [58%]
Third hottest: yellow supergiant [65%]
Coolest: red dwarf [75%]

Two stars (equally far away) have the same temperature, but one star is dimmer, and the other star is brighter. The __________ star will be larger in size.

dimmer.	**** [4]
brighter.	*********************************** [35]
(These stars would be the same size.)	[0]
(Unsure/guessing/lost/help!)	* [1]

Two stars (equally far away) have the same brightness, but one star is cooler, and the other star is hotter. The __________ star will be larger in size.

cooler.	********************* [21]
hotter.	*********** [11]
(These stars would be the same size.)	****** [6]
(Unsure/guessing/lost/help!)	** [2]

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

"Would you please make it known to me that you are actually reading my questions?" (Well, I can't guarantee that I actually read your question, but at the very least I cut-and-pasted your question here.)

"I remember a lot of these concepts from the pre-test we took the first day of class and it's making me feel smarter." (Better yet, let's see how much of this you retain for the post-test on these concepts.)

"I could definitely use some clarification of parallax and measuring distance in class."

"I don't really have a question, but I'm watching a 'star' low in the northwestern horizon that is very bright to see if it moves against the rest of the sky gradually, to see if it's possibly a planet! Have to go check on that now."

"How do you feel that we as a class are doing?" (You could all make happier. But that's just me.)

"Why do you love astronomy?" (Who doesn't love the stars? Or better yet, being able to teach about the stars.)

"What is the launch vehicle for the James Webb Space Telescope, and why did they choose it? (The Ariane 5, the very best rocket the European Space Agency has to offer.)

Online reading assignment: stellar parameters (NC campus)

Astronomy 210, spring semester 2015
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 parallax, distance, apparent magnitude, absolute magnitude, Wien's law and the Stefan-Boltzmann law.


Selected/edited responses are given below.

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

"The different spectral classes of the stars, O, B, A, F, G, K, and M. I knew that they were classified because of color and temperature, but I guess I never looked into how they are classified."

"The ratings of stars apparent magnitude and actual magnitude is interesting, because it is cool to rate things."

"The magnitude scale from +1 being the brightest to +6 and up getting dimmer. I understand that it means that the brightest star is in first place and all, but it is still interesting that it's that way."

"A small, really hot star can be as bright as a large star that is less hot."

"How the different colors of stars correlates to their temperatures."

"How to determine brightness interesting because I thought it was a way more difficult process than a mathematical equation."

"That red stars are cool and blue stars are hot. I thought it would be the other way around."

"The method for finding absolute magnitude of a star--moving all the stars to an equal distance of 10 parsecs and seeing which is actually the brightest is pretty cool and shows that the sun is pretty dim."

"How to tell the distance of a star through parallax interesting as I've always wondered how that was figured out."

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

"Trying to keep the laws of the luminosity/temperature/size of all these stars is going to be rather difficult, for me."

"Why is it that the negative numbers in absolute magnitude and apparent magnitude, actually make it brighter?"

"Parsecs, because it's just confusing"

"Nothing, really."

"Honestly I found everything confusing."

"How to measure the distance of stars, I understand that you take two different measurements, but I don't know how the measurements really work."

"I don't understand how parallax works."

"Something that I found confusing was the absolute magnitude. The numbers just threw me off. I did not understand how pushing stars back to 10 parsecs could make things more 'fair.'"

Explain how apparent magnitude and the absolute magnitude are defined differently.

"Apparent: the brightness of a star relative to an observer on Earth. Absolute: the true magnitude of a star, compensating for its distance from the observer on Earth."

"Apparent magnitude is how bright we see the star from Earth. Absolute magnitude is once the star is 10 parsces away from Earth and on an equal distance with the other stars and then judging the true brightness of the stars."
"I have no idea. I need help!!!"

"Absolute measures the actual brightness while the apparent measures the brightness as you see it."

"What it looks like and what it really is."

Suppose the sun was moved to a distance of 10 parsecs away. As a result, its __________ magnitude would become dimmer.

absolute.	******* [12]
apparent.	****************** [18]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	* [1]
(Unsure/guessing/lost/help!)	** [2]

Rank the brightnesses of these stars (1 = brightest, 4 = dimmest; there are no ties), as seen from Earth.
(Only correct responses shown.)

1 (brightest): the sun, m = -27 [85%]
2: Canopus, m = –1 [71%]
3: Vega, m = 0 [77%]
4 (dimmest): Kapteyn's star, m = +9 [71%]

Rank the brightnesses of these stars (1 = brightest, 4 = dimmest; there are no ties), if relocated to 10 parsecs from Earth.
(Only correct responses shown.)

1 (brightest): Canopus, M = -3 [56%]
2: Vega, M = +0.5 [56%]
3: the sun, M = +5 [71%]
4 (dimmest): Kapteyn's star, M = +11 [68%]

Determine the stars that get dimmer or brighter when relocated from their original positions to 10 parsecs from Earth.
(Only correct responses shown.)

The sun: gets dimmer [68%]
Canopus: gets brighter [65%]
Vega: gets dimmer [60%]
Kapteyn's star: gets dimmer [60%]

Rank the temperatures of these main sequence stars (1 = hottest, 4 = coolest; there are no ties).
(Only correct responses shown.)

Hottest: blue main sequence star [65%]
Second hottest: white main sequence star [59%]
Third hottest: yellow main sequence star [77%]
Coolest: red main sequence star [77%]

Rank the temperatures of these supergiant and dwarf stars (1 = hottest, 4 = coolest; there are no ties).
(Only correct responses shown.)

Hottest: blue supergiant [62%]
Second hottest: white dwarf [47%]
Third hottest: yellow supergiant [53%]
Coolest: red dwarf [77%]

Two stars (equally far away) have the same temperature, but one star is dimmer, and the other star is brighter. The __________ star will be larger in size.

dimmer.	*** [3]
brighter.	************************* [25]
(These stars would be the same size.)	** [2]
(Unsure/guessing/lost/help!)	**** [4]

Two stars (equally far away) have the same brightness, but one star is cooler, and the other star is hotter. The __________ star will be larger in size.

cooler.	************* [13]
hotter.	************** [14]
(These stars would be the same size.)	** [2]
(Unsure/guessing/lost/help!)	***** [5]

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

"I like turtles."

"I'm mad at Doctor Who because he traveled to a blue star that was supposed to be the coldest star in the universe. Cold stars aren't blue. Fail."

"When will we do another observation night?" (Next Thursday, weather permitting.)

"The textbook says brown dwarfs are a step above gas giants, so are gas giants just stars that didn't quite make it?" (In a way, yes. Stars fuse hydrogen into helium in their cores; this requires a lot of gravitational forces in their cores, so stars need to have a certain amount of mass in order to do this. Brown dwarfs don't have enough mass (and gravity) to fuse hydrogen into helium, but they can fuse hydrogen into deuterium, which is a step down from helium. And a gas giant planet is also made of hydrogen, but does not have enough mass (and gravity) to fuse its hydrogen into anything at all, so it will just stay that way.)

Astronomy quiz question: redshift vs. blueshift

Astronomy 210 Quiz 4, fall semester 2010
Cuesta College, San Luis Obispo, CA

[Version 1]

The (simplified) absorption lines for Iota Sagittarii, a K0 giant, are shown at right. (The arrows indicate the expected wavelength values for a stationary K0 giant.)

Based on its absorption line wavelength values, Iota Sagittarii must be a star:
(A) located a little farther away than 1 parsec.
(B) located closer than 1 parsec.
(C) moving towards Earth.
(D) moving away from Earth.

Correct answer: (D)

The absorption lines for Iota Sagittarii are shifted towards slightly larger values ("redshifted"), indicating that it is moving away from Earth.

Section 70158
(A) : 7 students
(B) : 4 students
(C) : 13 students
(D) : 20 students
(No response: 1 student)

"Success level": 47% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75

[Version 2]

The (simplified) absorption lines for Procyon A, a F5 main sequence star, are shown at right. (The arrows indicate the expected wavelength values for a stationary F5 star.)

Based on its absorption line wavelength values, Procyon A must be a star:
(A) located a little farther away than 1 parsec.
(B) located closer than 1 parsec.
(C) moving towards Earth.
(D) moving away from Earth.

Correct answer: (C)

The absorption lines for Procyon A are shifted towards slightly smaller values ("blueshifted"), indicating that it is moving towards Earth.

Section 70160
(A) : 5 students
(B) : 3 students
(C) : 20 students
(D) : 14 students

"Success level": 52% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.82

Astronomy current events question: Scholz's star pass-by

Astronomy 210L, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Leonor Sierra, "A Close Call of 0.8 Light Years," (February 16, 2015)
http://www.rochester.edu/newscenter/scholz-star/

WISE J072003.20-084651.2, or "Scholz’s star" passed through the outer edge of our solar system 70,000 years ago, based on:
(A) comet orbits.
(B) its speed and trajectory.
(C) ancient petroglyphs.
(D) solar flare anomalies.
(E) iridium-rich sediments.

Correct answer: (B)

Student responses
Sections 30678, 30679, 30680
(A) : 7 students
(B) : 34 students
(C) : 2 students
(D) : 9 students
(E) : 1 student

Astronomy current events question: extreme mass-ratio binaries

Astronomy 210L, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Christine Pulliam, "Mismatched Twin Stars Spotted in the Delivery Room," (February 12, 2015)
https://www.cfa.harvard.edu/news/2015-06

Mismatched stars in extreme mass-ratio binaries in the Large Magellanic Cloud are identified when they:
(A) emit x-ray pulses.
(B) undergo nova explosions.
(C) produce solar flares.
(D) pass in front of each other.
(E) transfer hydrogen between them.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 3 students
(B) : 7 students
(C) : 8 students
(D) : 33 students
(E) : 2 students

Astronomy current events question: multiple supernova images

Astronomy 210L, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Donna Weaver, Ray Villard, Patrick Kelly, and Steve Rodney, "Hubble Sees Supernova Split into Four Images by Cosmic Lens," (March 5, 2015)
http://hubblesite.org/newscenter/archive/releases/2015/08/full/

Due to gravitational lensing by the MACS J1149.6+2223 cluster of galaxies, the Hubble Space Telescope observed a supernova:
(A) split into multiple images.
(B) falling into a supermassive black hole.
(C) moving back in time.
(D) just before it actually exploded.
(E) converted into dark matter.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 37 students
(B) : 1 student
(C) : 1 student
(D) : 7 students
(E) : 6 students

Online reading assignment: circuit analysis

Physics 205B, spring semester 2015
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 circuit analysis.


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.

"Kirchhoff’s junction rule states that the sum of the currents that flow into a junction— any electric connection—must equal the sum of the currents that flow out of the same junction. The junction rule is a consequence of the law of conservation of charge. Since charge does not continually build up at a junction, the net rate of flow of charge into the junction must be zero."

"I understand the basics about Kirchoffs law, it seems very simple, what comes in must come out. And the loop rule where the net change in voltage must equal zero."

"Resistors can be in a series or in parallel. In series the total resistance is the sum of all the resistors in series. In parallel the total resistance is the inverse of the sum of the reciprocals of all the resistors in parallel. When going through a resistor, the electrical potential decreases as you go with the current and rises flowing against the current. You consider whether you are going from negative to positive or positive to negative for potential rises and drops through an emf."

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 was confused as why we would only care about the flow of electrons in a circuit not the direction of the current. I don't get why they wouldn't both flow in the same direction."

"The concepts don't seem all that confusing."

"The rise and drops of electronic potential is hard for me to understand I would like more explanation in class. I would like to see in class problems."

"For resistors in series, voltage drops according to ∆V = I·Rm and yet the same current passes through all the resistors? And for resistors in parallel, they all receive the same drop in ∆V, and yet the current is split between them?"

Determine what happens to the following parameters as current flows through an ideal wire.
(Only correct responses shown.)

Current: remains the same [64%]
Voltage: remains the same [53%]

Determine what happens to the following parameters if you go through a resistor along the direction of current.
(Only correct responses shown.)

Current: remains the same [42%]
Voltage: decreases [58%]

Determine what happens to the following parameters if you go through into the (-) terminal and out of the (+) terminal of an ideal battery.
(Only correct responses shown.)

Current: remains the same [42%]
Voltage: increases [42%]

Briefly explain what quantity is conserved when applying Kirchhoff's junction rule.

"The sum of the currents into or out of any junction in the circuit is zero."

"Charge flow per time is conserved."

"Current is conserved."

"Charge is being conserved. Thus the currents into a junction must equal the sum of all currents flowing out of that same junction."

Briefly explain what quantity is conserved when applying Kirchhoff's loop rule.

"Electric potential energy per charge."

"Electric potential is conserved. For any path in a circuit that starts and ends at the same point the sum of electric potential change is zero."

"Voltage is conserved I believe but I am not quite sure."

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

"Is there any way to do one big problem using all the aspects of circuits. if so I would like to do one." (No, baby steps. But each baby step will be gigantic.)

"One of life's rules: Do not become part of the circuit."

"I can't believe we are already half way to the end of the semester. I got a tutor to help me kick butt and take names on the upcoming midterm:-) Could you please give us an idea of what are primary focus of study should be this weekend for the midterm?" (The list of midterm-like problems is now posted, as well as the study guide for the midterm.) "

Online reading assignment question: helpful/unhelpful astronomy midterm study tips

Astronomy 210, spring semester 2015
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.

Describe something notable that either helped or did not help with studying for this midterm. Selected comments may be discussed in class. (Graded for completion.)

The following are all of the student responses to this question, verbatim and unedited.

"If you read the book when it's time almost after you've heard the story then it stick with you more"

"What helps me study is making sure I have everything I need. Having a computer near by so if something doesn't make sense I could watch videos. Eliminating all distractions, drinking water. Making sure you're not tired etc. No-brainer type stuff"

"all of the metaphors used to describe certain aspects of astronomy have helped me to remember them much more efficiently."

"I like drawing diagrams because they help me visualize what I'm learning, and when it is just regular notes I use highlighter to make certain topics pop."

"I really did like the doing the study session we did in class but the haiku were a bit confusiong but when we worked on the word problem that was really helpful it made me a little less nervous for the mid term and now I know what to expect when it comes to the word problems"

"Going over the in class activities has helped focusing the concepts in my mind Also the midterm short answer example questions helped a lot"

"Watching tv does not help you study. Looking over old quizzes will help."

"Neutral"

"Going back through the online presentations as well as the book is helpful to cover the basics of what you need."

"I'm going to focus on the slides more than the book. The book's good for clarifying some things but I think there's a bit too much information in the book to make it a good study guide by itself. I like to cook so the analogies between space and food really hit home in ways I don't think the book ever could."

"Something that helps study during this midterm is doing the flashcard questions and going back on them as well as printing out in class activities and going back on those 2."

"Reviewing the quizzes will be essential!"

"It's helpful to go over slides and discuss things in class that the class as a whole is struggling with. It is helfpul to hear other class mates in put and thoughts/questions on things."

"Reviewing the keywords in the yellow boxes in the textbook."

"The online presentations help a lot and just reading over the book. The book has all the information we will need to know and if it's confusing at first just re-read those sections."

"Those practice quizzes are extremely helpful, both the in-class ones and the ones posted on the website."

"the different diagrams and visuals given (i.e. the moon phases and times picture was very helpful)"

"Having something tangible like the star wheel or drawing out the moon phases helps me when studying because it gives me something to apply it to in order to use my brain rather than the book parts of having to memorize the astronomers and their specific laws."

"It helps to be able to go back into the material and presentation previews/course material to review a few things. For instance, I can look back at the astronomers."

"I think it will help to study the old quizzes"

"The star wheel helps because I am able to try and find any constellation which helps me be more comfortable using it and being prepared to use it on the midterm."

"For me reviewing past exams has helped. Although, I am nervous about the 20 point questions and reviewing the examples on the blog is key."

"Going back over in-class activities and quizes"

"flash cards quiz"

"The little picture we made to find when the moon set and rose that day, also the moving pictures."

"Something that helps is drawing charts/diagrams over and over again so you memorize it"

"notes,textbook,youtube,google,previous tests"

"Reviewing in class is helpful but just re reading could help."

"It helps to group up with people that are good at explaining things. I wish we would have gone over more problems in class that would prepare us better."

"examples are amazing to have available. However I would love to have an answer key readily available on the site for the practice tests. That would make it so much more convienent and easier to study. In general I'm a bad test taker period I feel like I know my stuff however the way the test asks questions (the vagueness) for me is either going to save or destroy me. hopefully the earlier option."

"flash cards"

"Going over previous quizzes and using the study guide provided will be the key to me achieving a good grade on this exam. I don't think reading through the chapters in the book will do it for me honestly."

"group studying!"

"It helps to actually draw when thinking about the sun and moon phases for me. It just helps to not get confused in your own head."

"It really helped me to do the flashcard questions to study for the midterm!"

"Having all the in class activities and past quizzes online really helps with studying for the midterm because I can print them out and re do them to study."

"All of the pictures, drawings, and illustrations really help in understanding some tough concepts which might be harder to explain in words alone."

"Reading directly from the book has been helpful for me"

"Groupstudy"

"I cannot figure out the flash cards to be used for which day, since they are posted on different days that do not correlate to the quizzes. I keep studying for the wrong test's because of this. I also find the blog difficult to navigate."

"Having the past essays to look at helped."

"Class discussions and activities help me learn the material."

"The short answer examples/answers are really helpful to study"

"It is extremely confusing to me how to use the star chart still, as well as how to answer the short answer questions, if you say there isn't a correct answer…?"

"Confused on how in you word some of the questions"

"I think the Review Questions in the book at the end of the chapter are much more specific than what you are looking for us to walk away with."

"It would have been more helpful to have a study guide like for the quizzes posted including the answers so I actually know if I'm getting the right answer."

"Any example with a picture or image that shows the actual process of what ever is being explained helps a lot. The quizzes online and midterm where great for studying, I feel a lot more confident now."

"Going over all of the quizzes is very helpful. Going over the flashcards is helpful. Studying with someone that knows what there talking about is helpful. Knowing the concepts is really helpful instead of just memorizing things."

"studying with a partner."

"Going through all of the quizzes and in-class activities is helpful."

"Going over the quizzes helps and looking over the past exam questions."

"Passion for the subject, if you have that you don't need flash cards or highlighters. It is incredible the amount of information one can retain and apply when fascination is the driving force in understanding."

"looking over sample questions"

"making a study guide by re writing notes and quizzes"

"not having PDOG present to help me study does no help!"

"GOING TO THE PROFESSORS OFFICE HOURS HELPS, HELPS, and HELPS!"

"tv doesn't help."

"Listening to music helps me study."

"Making flashcards."

"It helps me to read through my notes and the book a lot. I have a hard time remembering things for tests and quizzes and just need to do a lot of reading over what we do in class."

"Quizzes and practice quizzes really helped and also the sample short answer questions and answers from past semesters."

"STUDY!!"

"the review in class we did was helpful!"

Presentation: star brightnesses

Look at these stars. Just look at them. And let's sort them by their brightnesses. But just their brightnesses, as we're going to ignore the colors of these stars (even though they do have different colors), and we're going to ignore the sizes of these stars as well (even though they do have different sizes). This is why the stars are represented here as squares that correspond to their relative brightnesses.

In this presentation we will discuss how star brightnesses are measured, and how we can determine whether a bright star or a dim star seen in the night sky is really bright or dim (or perhaps not really bright or dim).

Star brightnesses are measured using a magnitude scale, with +1 for bright stars, and +6 for the dim stars. If the smaller positive number for brighter stars bothers you, think of ranking schemes (as did the ancient Greeks in originally setting up this scale), where the brightest stars are "first place" or "top tier" stars, and the dimmest stars are in "sixth place" or "bottom tier" stars. And the scale did need to get revised, as there a few stars that blow the top off the original +1 to +6 scale. Brighter than the "first place" +1 stars are "zero place" stars, and brighter than those stars are "–1 place" stars. These are the very bright stars, and the scale has larger negative numbers for progressively brighter stars. There are also lots of stars dimmer than +6, and the scale has larger positive numbers for progressively dimmer stars.

The apparent magnitude m (lower case italics "m") of a star is the "as is" brightness as seen by an observer on Earth, without compensating for distance. The sun is not the brightest star ever, but being extremely close makes it seem brighter than all other stars. Deneb is one of the brightest stars ever, but being extremely far away makes it seem dimmer than many other stars. So, apparent magnitude is not really a fair way to compare the brightnesses of stars, as some stars cheat (like our sun), and some stars get dissed (like Deneb).

In order to compensate for the effect of distances on star brightnesses, we need to be able to measure their distances. This is done using parallax, which is the shift in perspective as you look at an object from two different viewpoints, such as Diane Lane's left eye and right eye in Under the Tuscan Sun (Blue Gardenia Productions/Buena Vista Pictures, 2003).

In astronomy the two different viewpoints for looking at a star is from Earth when it is at one end of its orbit, then six months later from Earth when it is at the other end of its orbit. In this case the nearby star will appear to shift back and forth, and the amount of this shift (its parallax) can be related to its distance.

Again we look at a star from Earth when it is at one end of its orbit, then six months later from Earth when it is at the other end of its orbit, but this time the star is farther away. In this case the distant star will appear to shift back and forth a smaller amount, and the smaller amount of this shift (a smaller parallax) can be related to a greater distance. In practice, this shift is an angle measured not in degrees, but in very small units of arc seconds (where 1 arc second is 1/3,600th of a degree), and a star that shifts by 1 arcsecond corresponds to being at a distance of 1 parsec away ("a parallax angle of 1 arc second"), or 3.26 light years away. Parallax shifts bigger than 1 arc second would correspond to stars closer than 1 parsec away, while parallax shifts smaller than 1 arc second would correspond to stars farther than 1 parsec away.

Now that we have one method (actually several other methods are also used) to determine how close or how far away a star is, we can then determine the actual brightness of a star by compensating for its distance. In the case of the sun, we know that it is extremely close, and if we conceptually push it back to an arbitrary "fair comparison distance" of 10 parsecs away, it will get dimmer.

Similarly for Deneb, we know that it is extremely far away, and if we conceptually bring to closer to the arbitrary "fair comparison distance" of 10 parsecs away (just like we did for the sun), it will get brighter.

And now that we have compensated for the extreme closeness of the sun and the extreme distance of Deneb by conceptually relocating them to the same "fair comparison distance" of 10 parsecs away, we can see that the sun is actually much dimmer than Deneb. The brightnesses of stars when placed 10 parsecs away is their absolute magnitude M (actually, upper-case cursive "M"), and if we conceptually relocate every other star to 10 parsecs (once we know their actual distances), absolute magnitude becomes a way to compare the "actual" brightnesses of stars with each other, something that will be important in the next presentation on star temperatures and sizes.

Let's practice applying these concepts to some stars.

Rank these stars from brightest to dimmest, as seen from Earth:

______, _____, _____, _____.

Rank these stars from brightest to dimmest, if relocated to 10 parsecs from Earth.

______, _____, _____, _____.

List the star(s) (if any) that get dimmer when relocated from their original positions to 10 parsecs from Earth (these are the stars that are located nearer than 10 parsecs from Earth).

______, _____, _____, _____.

List the star(s) (if any) that get brighter when relocated from their original positions to 10 parsecs from Earth (these are the stars that are located farther than 10 parsecs from Earth).

______, _____, _____, _____.