The `6563 Å H_(2)` line emitted by hydrogen in a star is found to be red shifted by `15 Å`. Estimate the speed with which the star is receding from earth.
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Here, `lambda = 6563 Å, Delta lamnda = + 15 Å, c = 3 xx 10^(8)ms^(-1)` Since the star is receding away, hence its velocity `v` is negative (i.e. if `Delta lambda` positive, `v` is negative) `:. Delta lambda = - v lambda//c or v = -(c Delta lambda)/(lambda) = -(3 xx 10^(8) xx 15)/(6563) = - 6.86 xx 10^(5) ms^(-1)` Here, negative sign shows recession of star.
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