# help please?

a hydrogen line in a star's spectrum has a frequency of 6.17*10^14 hz when stationary. In rigels spectrum it is shifted upward by 4.26*10^10 hz what is rigels velocity relative to us

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- Anonymous5 months agoBest answer
To a good approximation v/c = Δf/f₀

v = cΔf/f₀

= 3x10^8 x 4.26x10^10/(6.17x10^14)

= 2.07x10^4 m/s

By the way, it's 'Hz', not 'hz'.

- nyphdinmdLv 75 months ago
YOu know f0 = 6.17x10^14 Hz and the blue shifted line is f0+df = f' = 6.17x10^14 + 4.26x10^10 Hz

SInce this is blue shited we can use the doppler effect

f' = f0*(c/(c-v)) where v = speed of Rigel

Note df = f' - f0 = f0*(c/(c-v) - 1) = f0*(v/(c-v)) ---> solve for v

v = df/(f0 + df) c --> plug in values ---> v = 2071 m/s

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