## 20140325

### Online reading assignment: stellar parameters (NC campus)

Astronomy 210, spring semester 2014
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.
"I found the idea of surveying the stars interesting because I had no idea so much of the universe has already been mapped out and it's all happening in my lifetime."

"I liked reading about the distances between the stars. Measuring between such great distances is fascinating."

"Using the color of stars to determine their temperature."

"I thought it was interesting finding out that you can tell how hot a star is relative to another by color--I would have guessed it would be more complicated than that."

"The H-R diagram is very interesting to me because this is a handy visual tool to understand the luminosities and temperatures of stars and how they relate to other stars. Their spectral types are noted and whether they are in main sequence stars, supergiants, giants, red dwarfs or white dwarfs. Cool stuff."

"I found it interesting that red is cooler then blue! I thought that red was always considered a hot color and blue was a cool color."

"A simple math equation can be used to tell one of three quantities (temperature, luminosity, and brightness) of stars. Math seemed to be my strongest subject."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I found measuring the distance of stars confusing. There are a few methods but they'll all math/formula related which aren't my strong suit."

"I need clarification on absolute and apparent magnitude. I have some idea, but I'm not 100% sure."

"The process of determining the distance of a star was confusing. I think it was confusing because the parallax idea throws me off a bit."

"I still just don't really understand the whole luminosity thing and how the size makes the star dimmer or brighter."

Explain how apparent magnitude and the absolute magnitude are defined differently.
"Absolute is the intrinsic brightness of a star. Apparent is only how bright stars appear from Earth."

"The absolute magnitude is the apparent magnitude that star would have if it were 10 parsecs away (standard distance)."

"Absolute magnitude versus apparent magnitude is hard for me to explain."

Suppose the sun was moved to a distance of 10 parsecs away. As a result, its __________ magnitude would become dimmer.
 absolute. ********** [10] apparent. *********** [11] (Both of the above choices.) **** [4] (Neither of the above choices.) [0] (Unsure/guessing/lost/help!) [0]

Rank the temperatures of these stars (1 = hottest, 4 = coolest; there are no ties).
(Only correct responses shown.)
Hottest: blue supergiant [88%]
Second hottest: white dwarf [52%]
Third hottest: yellow supergiant [60%]
Coolest: red dwarf [84%]

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. ****** [6] brighter. ****************** [18] (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. ************ [12] hotter. ************ [12] (These stars would be the same size.) * [1] (Unsure/guessing/lost/help!) [0]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I like how in the book they compare the H-R diagram to a diagram about horsepower vs. weight for cars. It gave me a better understanding of how the H-R diagram works."

"This star talk is really moving us into an interesting chapter!"