Physics 341: Problem Set #11 due November 20 1. Light from the H ↵ transition of hydrogen is emitted at a wavelength λ = 656 . 28 nm. Recall that for light, λ⌫ = c . (a) Consider a star moving directly away from an observer on Earth at a speed v = 13 , 000 km s-1 (like the stars speeding around Sgr A*). At what wavelength would the H ↵ spectral line be observed? (b) Imagine instead the star is moving perpendicular to our line of sight (in other words, “in the plane of the sky”) with a transverse velocity v = 13 , 000 km s-1 . Now at what wavelength would the H ↵ line be observed? Hint: You can consider light to be a “clock” with a frequency ⌫ . (c) What would your answers be for parts (a) and (b) if you neglected special rela-tivity? a distance of approximately 8 light-years as measured from Earth, at a speed of u =0 . 8. (You may work in units with
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