With what speed should a star move with respect to us so that the beam at wavelength 460.0 nm is observed at 460.8 nm.

Explanation

Now we have, `(Deltav)/v=(Delta lamda)/lamda=(-v_(radial))/c`
Now, `Delta lamda=(460.8-460.0)nm=0.8nm`
Now `v_(radial)=(c Delta lamda)/lamda`
`=(3 times 10^8 times 0.8nm)/(460 nm)`
`=5.217 times 10^5 m//s`
`approx 521.7km//s`
Since, v comes out to be positive hence we can conclude that the star is moving away from us.