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# dis9-slides - ASTR 100 Discussion 9 Nov 7 2011 1 The star...

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ASTR 100 Discussion 9 Nov. 7, 2011

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1. The star Polaris is located 133 pc away in Ursa Minor. When astronomers observe the spectrum of Polaris, the continuous spectrum part has its brightest light at a wavelength of 400 nm. What is the surface temperature of Polaris? Show your work. Your answer must be in proper scientific notation – no fractions.
Answer: We need to use Wien's Law to calculate this. T = 2.9 × 10 6 nm K max In this case, max = 400 nm = 4 x 10 2 nm. T = 2.9 × 10 6 nm K 4 × 10 2 nm = 0.7 × 10 4 K T = 7 × 10 3 K The surface temperature of Polaris is 7 x 10 3 K.

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Grading checklist: Did you write down your equation? Did you use the correct input value? Did you put your answer in proper scientific notation? Did you have the right units?
2. Which ONE of the following statements gives the correct cause and effect relationship for a star's surface temperature and color? In your answer, explain how the cause causes the effect. a. “The star is hot because it is blue.” b. “The star is blue because it is hot.”

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Answer: This excelletn answer was written by a student: “B. The star is blue because it is hot. Since it is hot it is giving off more energetic light. The more energetic the light is the short[er] its wavelength. Since blue has one of the shortest wavelengths of visible light[,] we see objects that have energetic wavelengths as blue.”
Grading checklist: Did you choose the correct statement? Did you explain how a star's surface temperature affects what wavelengths of light it emits?

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dis9-slides - ASTR 100 Discussion 9 Nov 7 2011 1 The star...

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