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What speed should a galaxy move with respect to use so that the sodium line at 589.0 nm is oberved at 589.6 nm ?

Answer» Since, `v lambda=c, (Deltav)/v=(Deltalambda)/(lambda)` (for small changes in v and `lambda)`. For `Deltalambda =589.6-589.0=+0.6nm`
we get [using Equation `=(Deltav)/(v)=(upsilon_("radial"))/(c)]`
`(Deltav)/(v)=-(Deltalambda)/(lambda)=-(upsilon_("radical"))/(c)`
or `upsilon_("radical")cong +c ((0.6)/(589.0))=+3.06xx10^(5)m s^(-1)=306km//s`
Therefore, the galaxy is moving away from us.


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