Astronomy midterm question: determining distance from apparent and absolute magnitudes (1)

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[*]:

0725: Let's say a star had an apparent magnitude of –1.5 and an absolute magnitude of +1.5. The star has to be closer than 10 parsecs from Earth.

Discuss whether this claim is correct or incorrect, and how you know this. Explain using the relationships between apparent magnitude, absolute magnitude, and distance.

[*] waiferx.blogspot.com/2008/11/astronomy-midterm-question-apparent.html.

Solution and grading rubric:

• p:
  Correct. Understands difference between apparent magnitude m (brightness as seen from Earth, while at its actual distance from Earth) and absolute magnitude M (brightness as seen from Earth, when placed at the "fair comparison distance" of 10 parsecs away), and discusses:
  1. the star's apparent magnitude of m = −1.5 is brighter than its absolute magnitude of M = +1.5; so
  2. the star must be located closer than 10 parsecs away, as moving it from its actual location (where m = −1.5) to 10 parsecs (where M = +1.5) makes it dimmer; such that
  3. the student's claim is correct.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Has both (1)-(2) complete and correct, but somehow concludes that student's claim is incorrect, or does not sufficiently discuss the correctness/incorrectness about the student's claim.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of relationships between apparent magnitudes, absolute magnitudes, and distances. At least discussion demonstrates understanding of relationships between apparent magnitudes, absolute magnitudes, and distances. Has only one of (1)-(2) complete and correct, the other is problematic.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use relationships between apparent magnitudes, absolute magnitudes, and distances. Both (1) and (2) are problematic.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on garbled definitions of, or not based on proper relationships between apparent magnitudes, absolute magnitudes, and distances.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm02Rf0w
p: 23 students
r: 4 students
t: 1 student
v: 0 students
x: 6 students
y: 0 students
z: 0 students

A sample "p" response (from student 1492):

Astronomy midterm question: determining distance from apparent and absolute magnitudes (2)

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[*]:

7734: If a star has an absolute magnitude of +20, but when seen from Earth has an apparent magnitude of +5, the star must be very close to us.

Discuss why this claim is incorrect, and how you know this. Explain using the relationships between apparent magnitude, absolute magnitude, and distance.

[*] waiferx.blogspot.com/2010/11/astronomy-midterm-question-apparent.html.

Solution and grading rubric:

• p:
  Correct. Understands difference between apparent magnitude m (brightness as seen from Earth, while at its actual distance from Earth) and absolute magnitude M (brightness as seen from Earth, when placed at the "fair comparison distance" of 10 parsecs away), and discusses:
  1. the star's apparent magnitude of m = +5 is brighter than its absolute magnitude of M = +20; so
  2. the star must be located closer than 10 parsecs away, as moving it from its actual location (where m = +5) to 10 parsecs (where M = +20) makes it dimmer; such that
  3. the student's claim is correct.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Has both (1)-(2) complete and correct, but somehow concludes that student's claim is incorrect, or does not sufficiently discuss the correctness/incorrectness about the student's claim.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of relationships between apparent magnitudes, absolute magnitudes, and distances. At least discussion demonstrates understanding of relationships between apparent magnitudes, absolute magnitudes, and distances. Has only one of (1)-(2) complete and correct, the other is problematic.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use relationships between apparent magnitudes, absolute magnitudes, and distances. Both (1) and (2) are problematic.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on garbled definitions of, or not based on proper relationships between apparent magnitudes, absolute magnitudes, and distances.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70160
Exam code: midterm02T4qz
p: 7 students
r: 4 students
t: 6 students
v: 3 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 5622):

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 archive: sun/spectra/star properties

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

Section 70158, version 1
Exam code: quiz05Sh0w


Section 70158

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

Section 70160, version 1
Exam code: quiz05NpRm


Section 70160

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

Online reading assignment: stellar parameters (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 parallax, distance, apparent magnitude, absolute magnitude, Wien's law and the Stefan-Boltzmann law, and a TED-Ed talk on stellar properties.


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 never really knew how brightness was measured, and it was cool to learn about."

"That stars can be much, much brighter than the sun."

"The way we can measure distance of stars using parallax is crazy!"

"How simply by using color spectra and basic parallax (trigonometry) ideas, we can determine sizes, distances, and temperatures of very distant stars."

"How the hotter stars are a blue color while the coolest stars are red. I initially assumed that the red stars would be hotter as we associate the color red with hot things. Now I know differently!"

"In astronomy, temperature is a number that relates to the average speed of a particle. I found it interesting because it's not defined as the term we use often."

"I'm glad to learn about Wien's law (how color of stars relate to their temperature). When we took the general astronomy knowledge test on the first day of class, I was completely lost on this subject."

"I found learning about stars to be really interesting, especially being able to tell the stars temperature by their colors."

"When looking at Wien's law, I found it very interesting that extremely cool stars colder than red give off infrared light, while extremely hot stars will give off ultraviolet light. It's weird to imagine extremely cool stars being infrared and non-visible. This makes me wonder if all stars were a visible temperature, how much different would the night sky look?"

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

"I found the magnitude scale a bit confusing at first because my brain didn't like the switch of high negative numbers defining the brightest stars and high positive numbers defining the dimmer stars."

"Parallax, stellar parallax, and parsecs are a confusing set of concepts for me to wrap my head around. It is difficult for me to understand a visual representation of parallax."

"The math in the two laws for blackbody radiation. Seeing some examples will help."

"I found that the Stefan-Boltzmann law was confusing because I'm not to sure what luminosity means. It just seems way more complex than Wien's law."

"Stefan-Boltzmann law. I don't understand it completely."

"This week's assignment had A LOT of new terms and ideas. Each individual idea is relatively easy to grasp given enough time to think about it. The problem, for me, was that there were just too many new things to take in and digest. I don't think I clearly understood most of this weeks reading. And for the first time, the blogs didn't really help understand the topic at hand; up until now they usually have."

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

"Apparent magnitude is how bright a star looks from Earth and absolute magnitude is how bright the star from 32.6 light years (10 parsecs) away."

"Apparent magnitude is the brightness of a star 'as is' seen by an observer on Earth without the compensation for distance. The absolute magnitude of a star is its observed brightness when moved to the 'fair comparison distance' of 10 parsecs away. Absolute magnitude helps us compare the actual brightness of stars."

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

absolute.	*********** [11]
apparent.	************** [14]
(Both of the above choices.)	[0]
(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 [96%]
2: Canopus, m = –1 [92%]
3: Vega, m = 0 [88%]
4 (dimmest): Kapteyn's star, m = +9 [92%]

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 [88%]
2: Vega, M = +0.5 [92%]
3: the sun, M = +5 [88%]
4 (dimmest): Kapteyn's star, M = +11 [92%]

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

The sun: gets dimmer [88%]
Canopus: gets brighter [88%]
Vega: gets dimmer [58%]
Kapteyn's star: gets dimmer [62%]

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 [85%]
Second hottest: white main sequence star [85%]
Third hottest: yellow main sequence star [92%]
Coolest: red main sequence star [85%]

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

Hottest: blue supergiant [96%]
Second hottest: white dwarf [73%]
Third hottest: yellow supergiant [69%]
Coolest: red dwarf [88%]

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.

less luminous.	**** [4]
more luminous.	******************** [20]
(These stars would be the same size.)	* [1]
(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.	************* [13]
hotter.	****** [6]
(These stars would be the same size.)	*** [3]
(Unsure/guessing/lost/help!)	**** [4]

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

"Just a little more explanations for star brightnesses."

"Just little clarification questions."

"This might be off-topic, but how come nebulae are cloudy-looking?" (They literally are clouds, which are dust and gases randomly strewn out in space without any structure, unless affected by a shockwave if a star explodes nearby, or gravity if enough stuff starts to clump together inside the nebula.)

"Are stars' temperatures harder to measure the further away they are from Earth?" (As long as you can see the star's color, you'll know how hot it is.)

"What determines the how hot a star burns? I though they, at least, start off with the same fuel (hydrogen)." (We'll cover fusion and how quickly stars "burn" hydrogen next week.)

"The other night, I was able to show off my astronomy knowledge to my friends who had asked what AM and PM stood for. I was able to explain the ante-meridian and post-meridian concept, and it was cool having the ability to share with them the reasoning behind it!"

"Do we get extra credit if we go to see the SOFIA aircraft telescope?" (No, but good for you to get that chance this weekend. Also: pics, or it didn't happen.)

Online reading assignment: stellar parameters (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 parallax, distance, apparent magnitude, absolute magnitude, Wien's law and the Stefan-Boltzmann law, and a TED-Ed talk on stellar properties.


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.

"Parallax and the shift in perspective as you look at an object from two different viewpoints."

"Star brightnesses, because it is completely different from what you would think. It is more than just looking at the sky and saying that star is bright, it is understanding the science and the math behind it and that is what I want to learn about."

"That based on color one can determine the star's temperature."

"Learning about stars is interesting to me. There were different classifications of stars. Some where 10 to 100 times the diameter of the sun."

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

"I don't really understand how the magnitude of stars are determined."

"I would like to practice how to determine the brightness of the stars."

"Why are there parsecs? Not only is it ugly when you translate it to any other unit but it also isn't very unique--it's only about three times more than a light year; why do we need to use it?"

"How to determine the temperature and luminosity of a star, I don’t know how to rank them either."

"What I found confusing or would like a little bit more of an explanation would be how one star can be bigger than the other and other one can be hotter, but in the end both are equal in luminosity and that's what I can't figure out."

"Star spectral types--I don't entirely understand how you can tell the size and temperature of a star by looking at its spectral lines"

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

"Apparent magnitude is the magnitude of a celestial object as it is measured from Earth. Absolute magnitude is the brightness of a celestial object as it would be seen at a standard distance of 10 parsecs."

"Apparent magnitude is the way we see the star here on Earth. Absolute magnitude is the way to compare a star's actual brightness."

"Apparent magnitude is the lower case m of a star is the 'as is' brightness (ex. m = –27). Absolute magnitude is upper case M the brightnesses of stars when placed 10 parsecs away."

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

absolute.	***** [5]
apparent.	** [2]
(Both of the above choices.)	* [1]
(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 [78%]
2: Canopus, m = –1 [67%]
3: Vega, m = 0 [78%]
4 (dimmest): Kapteyn's star, m = +9 [78%]

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 [67%]
2: Vega, M = +0.5 [67%]
3: the sun, M = +5 [67%]
4 (dimmest): Kapteyn's star, M = +11 [100%]

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

The sun: gets dimmer [67%]
Canopus: gets brighter [44%]
Vega: gets dimmer [56%]
Kapteyn's star: gets dimmer [56%]

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 [78%]
Second hottest: white main sequence star [55%]
Third hottest: yellow main sequence star [78%]
Coolest: red main sequence star [100%]

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

Hottest: blue supergiant [56%]
Second hottest: white dwarf [44%]
Third hottest: yellow supergiant [89%]
Coolest: red dwarf [89%]

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.

less luminous.	*** [3]
more luminous.	*** [3]
(These stars would be the same size.)	** [2]
(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.	**** [4]
hotter.	*** [3]
(These stars would be the same size.)	* [1]
(Unsure/guessing/lost/help!)	* [1]

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

"How do you learn the temperature and size of a star from its brightness, and vice versa?"

"Need some help on how to determine if a star is hotter or cooler compared to other stars but I think I have the main idea about them."

"Can we review these topics?"

"No questions."

Astronomy midterm question: comparing distances from apparent and absolute magnitudes (1)

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

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

1022: For example, a star could have an apparent magnitude of –3 and an absolute magnitude of +8. This star would be closer to Earth than a star with an apparent magnitude of +8 and an absolute magnitude of +3.

Discuss why this claim is correct, and how you know this. Explain using the relationships between apparent magnitude, absolute magnitude, and distance.

[*] waiferx.blogspot.com/2013/05/astronomy-midterm-question-relative.html.

Solution and grading rubric:

• p:
  Correct. Understands difference between apparent magnitude m (brightness as seen from Earth, when placed at their actual distance from Earth) and absolute magnitude M (brightness as seen from Earth, when placed at the "comparison distance" of 10 parsecs away), and discusses:
  1. the m = −3, M = +8 star must be closer than 10 parsecs away, as moving it from its actual location to 10 parsecs makes it dimmer; and
  2. the m = +8, M = +3 star must be farther than 10 parsecs away, as moving it from its actual location to 10 parsecs makes it brighter; such that
  3. the m = −3, M = +8 star must be located closer to Earth than the m = +8, M = +3 star.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of relationships between apparent magnitudes, absolute magnitudes, and distances.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use relationships between apparent magnitudes, absolute magnitudes, and distances.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on garbled definitions of, or not based on proper relationships between apparent magnitudes, absolute magnitudes, and distances.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30674
Exam code: midterm02nwF7
p: 19 students
r: 1 student
t: 7 students
v: 4 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 2815):

Astronomy midterm question: comparing distances from apparent and absolute magnitudes (2)

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

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

1022: For example, a star could have an apparent magnitude of –3 and an absolute magnitude of +8. This star would be farther away from Earth than a star with an apparent magnitude of +8 and an absolute magnitude of +3.

Discuss why this claim is incorrect, and how you know this. Explain using the relationships between apparent magnitude, absolute magnitude, and distance.

[*] waiferx.blogspot.com/2013/05/astronomy-midterm-question-relative.html.

Solution and grading rubric:

• p:
  Correct. Understands difference between apparent magnitude m (brightness as seen from Earth, when placed at their actual distance from Earth) and absolute magnitude M (brightness as seen from Earth, when placed at the "comparison distance" of 10 parsecs away), and discusses:
  1. the m = −3, M = +8 star must be closer than 10 parsecs away, as moving it from its actual location to 10 parsecs makes it dimmer; and
  2. the m = +8, M = +3 star must be farther than 10 parsecs away, as moving it from its actual location to 10 parsecs makes it brighter; such that
  3. the m = −3, M = +8 star must be located closer to Earth than the m = +8, M = +3 star.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of relationships between apparent magnitudes, absolute magnitudes, and distances.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use relationships between apparent magnitudes, absolute magnitudes, and distances.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on garbled definitions of, or not based on proper relationships between apparent magnitudes, absolute magnitudes, and distances.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30676
Exam code: midterm02SpsR
p: 26 students
r: 2 students
t: 5 students
v: 5 students
x: 4 students
y: 0 students
z: 0 students

A sample "p" response (from student 4815):

Astronomy quiz question: comparing brightnesses of stars moved to 10 parsecs away

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

The apparent magnitudes and distances of two stars are listed below.

	m apparent magnitude	d distance (parsecs)
Alsafi	+4.7	5.8 pcs
Eltanin	+2.2	47 pcs

When placed at 10 parsecs away, the star that is brightest is:
(A) Alsafi.
(B) Eltanin.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

The absolute magnitude of a star is the brightness it has when placed 10 parsecs away from Earth. Alsafi has an apparent magnitude of +4.7 at 5.8 parsecs away from Earth, and so when placed at 10 parsecs away it will have an absolute magnitude that is dimmer than +4.7 (a larger positive number). Eltanin has an apparent magnitude of +2.2 at 47 parsecs away from Earth, and so when placed at 10 parsecs away it will have an absolute magnitude that is brighter than +2.2 (a smaller positive number, or a negative number). Thus when both stars are placed 10 parsecs away, Alsafi will be dimmer, while Eltanin will be brighter.

Section 30674
Exam code: quiz05NiR0
(A) : 17 students
(B) : 12 students
(C) : 1 student
(D) : 0 students

Success level: 59% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75

Section 30676
Exam code: quiz05S4re
(A) : 20 students
(B) : 18 students
(C) : 0 students
(D) : 0 students

Success level: 56% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.80

Astronomy quiz archive: sun/spectra/star properties

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

Section 30674, version 1
Exam code: quiz05NiR0


Section 30674

0- 8.0   :
8.5-16.0 :	**** [low = 11.0]
16.5-24.0 :	***********
24.5-32.0 :	****** [mean = 26.2 +/- 8.7]
32.5-40.0 :	********** [high = 40.0]

Section 30676, version 1
Exam code: quiz05S4re


Section 30676

0- 8.0   :	** [low = 2.5]
8.5-16.0 :	**
16.5-24.0 :	********
24.5-32.0 :	*********** [mean = 27.6 +/- 9.2]
32.5-40.0 :	*************** [high = 40.0]

Online reading assignment: stellar parameters (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 parallax, distance, apparent magnitude, absolute magnitude, Wien's law and the Stefan-Boltzmann law, and a TED-Ed talk on stellar properties.


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 liked the TED-Ed talk video because the visuals really helped solidify concepts from the video."

"The multiple ways that spectra can help determine the different characteristics of stars!"

"Using parallax to measure star distance was something I hadn't considered and thought that was a pretty cool concept."

"Parallax, because when I tried looking at a close object with one eye closed and then back and forth the object that was farther away did seem to move less than the closer object."

"How astronomers measure the distance of a star. I sometimes wondered how they did that, but now I see that its a process to do that. They take pictures from two points around Earth's orbit. They take one photograph and another six months later."

"That we can tell how far away something was by figuring out how far an object moved when viewed from two viewpoints, and then applied that knowledge on a larger scale using Earth's revolution around the sun! I really loved reading about how we learned how to figure that out in our book. Also, Gaia using these methods to provide the first 3D map of our galaxy hardly needs explaining why that's freaking amazing."

"One of my favorite songs is called 'Parsec.' Now the lyrics make way more sense!"

"That the brightness you see from Earth isn't actually a star's real brightness, like you could see a star that looks bright and one that looks dim but the dim one is actually brighter."

"That the sun 'cheats' in its brightness. I had never considered distance as a factor when comparing the brightness of the sun to other stars."

"The scale in which star brightness is measured--it is similar to the way that cross country running is scored. The team with the least points wins."

"That a negative magnitude represents the brightest stars."

"How there's a color code for determining a star's temperature because they are light years away."

"The color of a star is linked to its surface temperature. The hotter the star, the shorter the wavelength of light it will emit. The hottest ones are blue or blue-white, which are shorter wavelengths of light. Cooler ones are red or red-brown, which are longer wavelengths."

"Even though an object is blue it may actually be way hotter than an object that is red."

"How cooler colors (bluer colors) are from hotter stars. This is interesting because when I was a film major, blue lights also have a higher color temperature despite being used for cool atmosphere."

"I really enjoyed looking over what other students found either helpful or unhelpful when studying for tests and midterms. I was able to compare my studying habits with theirs and see in what areas I could improve."

"Everything. I liked the whole lesson."

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

"Jow to rank the brightness of the star the apparent magnitude and absolute magnitude."

"In particular, I thought that the difference between absolute and apparent magnitude was confusing and I had trouble making the distinction."

"I could use some clarification on the apparent magnitude and magnitude scale."

"Parallax is kind of confusing to me. If we are to measure the distance of stars, how do we change our perspective from Earth?"

"Small parallax versus large parallax."

"If the sun is closer than some of the brighter stars, then in my head moving both objects to 10 parsecs away would still make the sun seem brighter than the other objects?"

"I do not understand parsecs at all."

"Star colors because they all look the same color from here at least to me."

"I found the Stefan-Boltzmann law to be confusing because even after reading through it twice, I'm still lost."

"The math behind star size and brightness. Maff is hard :("

"There's a lot to grasp in this section for me at this moment because I need more examples."

"Nothing so far."

"Everything was straightforward."

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

"Apparent magnitude is the brightness of something in space as perceived from Earth. Absolute magnitude is the brightness of something in space as it actually is."

"Absolute magnitude compensates for distance, whereas apparent magnitude is the 'as is' view an observer on Earth has."

"Apparent magnitude measures the brightness of the star from Earth, not taking distance into account. Absolute magnitude equalizes all star at 10 parsecs so that distance doesn't affect the results."

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

absolute.	************** [14]
apparent.	*************** [15]
(Both of the above choices.)	** [2]
(Neither of the above choices.)	* [1]
(Unsure/guessing/lost/help!)	*** [3]

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 [86%]
2: Canopus, m = –1 [77%]
3: Vega, m = 0 [83%]
4 (dimmest): Kapteyn's star, m = +9 [83%]

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 [57%]
2: Vega, M = +0.5 [66%]
3: the sun, M = +5 [54%]
4 (dimmest): Kapteyn's star, M = +11 [66%]

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

The sun: gets dimmer [77%]
Canopus: gets brighter [69%]
Vega: gets dimmer [60%]
Kapteyn's star: gets dimmer [66%]

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 [80%]
Second hottest: white main sequence star [83%]
Third hottest: yellow main sequence star [83%]
Coolest: red main sequence star [86%]

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

Hottest: blue supergiant [83%]
Second hottest: white dwarf [69%]
Third hottest: yellow supergiant [77%]
Coolest: red dwarf [89%]

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.	***** [5]
brighter.	************************** [26]
(These stars would be the same size.)	* [1]
(Unsure/guessing/lost/help!)	*** [3]

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.	**************** [16]
hotter.	************* [13]
(These stars would be the same size.)	** [2]
(Unsure/guessing/lost/help!)	**** [4]

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

"Can you put a special lens on a telescope so that you can look directly at the sun?" (Actually, a metal-coated piece of glass. In fact, it only lets through only 0.00001% of the sun's light, such that you can see the sun safely, but everything else that you could possibly look at through it will be appear dark!)

"How can a star be way bigger than the sun?" (As we'll see when we survey all types of stars, our sun is actually a pretty average to low-average star in terms of brightness, temperature, and size. It is what it is.)

"Can you teach us tricks on how to remember all this information, please?" (I will.)

"Did you come up with this 'math but not math' method yourself? I love it! It's super-easy to understand." (Not my original idea, but I'm just adapting alternate approaches to doing math from a lot of different sources, even from my former students.)

"I'm confused about the dwarfs/supergiant's temperature and color. Is it the same for both?" (Yes, no matter what size the stars are, same color stars will have the same temperature.)

"A bigger star is hotter than a smaller star, regardless of color? Is this correct always?" (Not necessarily. For example, a red supergiant will be cooler than a white dwarf.)

"I found it interesting that hotter stars and cooler stars give off ultraviolet or infrared respectively that we can't see, but most stars give off light in the range we can see. It's so lucky that we are able to see such an adequate range, versus creatures like dogs. Sometimes, it feels like we were made to admire space." (Since our sun is an average warm star that gives off light with wavelengths between the ultraviolet and infrared, we've developed eyes that can see using this type of light. Otherwise we wouldn't be able to see anything in the daylight!)

"How is there room in your brain for all this?" (There is barely any room in my brain for all this stuff. That's why I need to teach it to you, so I can clear it out of my head.)

"I forget to do these assignments more than I could've hoped." (Then hopefully you won't forget to do the rest of these assignments.)

"I would love to know if I got the above answers right." (Part of the weekly online reading assignments is for you to read through the answers to these questions.)

"I'm actually pretty lost. I got the bits and pieces, but I just need help piecing them together."

"Can we go over this stuff in class and review what will be on the next quiz/exam please?" (Certainly. At least you've tried going over this stuff before coming to class, and have given me feedback on what you understand (or more importantly, don't understand) so I can best make use of time in class tonight.)

"Why are planets and stars so complex?!" (That's what makes them worth studying. Also that's what makes this class worth a transfer science credit.)

Online reading assignment: stellar parameters (NC 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 parallax, distance, apparent magnitude, absolute magnitude, Wien's law and the Stefan-Boltzmann law, and a TED-Ed talk on stellar properties.


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 like the idea of using parallax to determine distance of objects in the sky."

"It was cool learning about the differences in absolute and apparent magnitudes."

"Apparent magnitude and absolute magnitude are interesting. A star that is closer may appear as being very bright but if it is moved 10 parsecs away, it will get dimmer."

"When watching Star Wars, I had no idea what a 'parsec' was but I learned that it's the distance to an imaginary star that has a 'parallax of 1 arc second.' So now I know what Han Solo meant when he said he made the Kessel Run in 12 parsecs, which I found pretty interesting and cool."

"Blackbody radiation is interesting. That we as humans emit (infrared) light from our body heat is very cool."

"Blackbody radiation and finding the size of a star through its luminosity and color was pretty interesting."

"How colors correspond to temperature. This was interesting because it would be assumed that blue means cold but it is actually quite the opposite."

"Based on the color and intensity of light we can determine the size of an object. The deduction here seems pretty basic, but makes a ton of sense."

"I found the different colors of hotness to be interesting, because in my mind red is the hottest because of fires and things like that."

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

"I don't understand the difference the magnitude scale and the difference between apparent and absolute magnitude."

"The method of determining the distance of a star."

"The concept of parsecs. I really need to get some guidance on this when we have class next. I don't know how to understand the info I am receiving."

"The whole idea of measuring a parsec and a stellar parallax."

"I think the brightness scale is confusing."

"Telling which star is the brightest or dimmest."

"Everything. the distances, numbers, parsecs, magnitudes, temperatures--there's a lot..."

"The math equations are a little confusing."

"The Stefan-Boltzmann law."

"Something I found kind of confusing and could use a little bit more lecture on is the Hertzsprung-Russell (H-R) diagram. I think I understand the basics, but I'm also a little confused by it at the same time."

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

"Apparent magnitude is the measure of the brightness of a star as seen from Earth; while absolute magnitude is the measure of the brightness of a star seen from 10 parsecs away."

"Apparent magnitude is how bright it looks from Earth, and absolute magnitude is how bright the star appears at a standardized distance of 10 parsecs."

"Absolute magnitude is general brightness, apparent is brightness from its location."

"Absolute magnitude factors in the star's distance to Earth when looking at it, while apparent magnitude does not."

"I will know this by tomorrow I promise!"

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

absolute.	[6]
apparent.	***************** [17]
(Both of the above choices.)	** [2]
(Neither of the above choices.)	* [1]
(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 [74%]
2: Canopus, m = –1 [67%]
3: Vega, m = 0 [70%]
4 (dimmest): Kapteyn's star, m = +9 [78%]

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 [63%]
2: Vega, M = +0.5 [67%]
3: the sun, M = +5 [67%]
4 (dimmest): Kapteyn's star, M = +11 [74%]

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

The sun: gets dimmer [81%]
Canopus: gets brighter [74%]
Vega: gets dimmer [33%]
Kapteyn's star: gets dimmer [41%]

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 [67%]
Second hottest: white main sequence star [89%]
Third hottest: yellow main sequence star [70%]
Coolest: red main sequence star [89%]

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

Hottest: blue supergiant [63%]
Second hottest: white dwarf [63%]
Third hottest: yellow supergiant [67%]
Coolest: red dwarf [70%]

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.	********** [20]
(These stars would be the same size.)	* [1]
(Unsure/guessing/lost/help!)	** [2]

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.	*************** [15]
hotter.	******** [8]
(These stars would be the same size.)	** [2]
(Unsure/guessing/lost/help!)	** [2]

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

"Please help me with parsecs."

"The book mentions the 'intrinsic brightness' of a star. Is this similar to the absolute magnitude?" (Yes, both are ways of measuring the "true" brightnesses of stars.)

"What's the hardest thing for you to teach in this class?" (After the first midterm, the stuff we're covering this week: apparent/absolute magnitudes, and Wien/Stefan-Boltzmann laws.)

"Does an Earth-type planet that is capable of sustaining life have to orbit another star that is the same as ours?" (Well, maybe a medium-mass star like our sun, but also maybe a low-mass star like a red dwarf. As we'll see later this semester, it is not likely that an Earth-like planet around a massive star would be capable of sustaining life, due to the very short lifetime of the massive star.)

"Really random question: what happens if you landed near the Milky Way? Will you die?" (Our solar system is located in the Milky Way, which is our own galaxy.)

"Will you be reading some of these questions in class anytime soon?" (Sometimes, although part of the weekly online reading assignments is for you to read through the answers to these questions.)

"I swear I read the textbook! Just not in time for the reading assignments, I guess..."

"Coffee or tea?" (Coffee.)