[填空题]
Through some coincidence, the Balmer lines froma7 rb :k jsw/0wf/z8df singly io,bjg0)hbo 8o nnized helium in a distant star happen to overlap with the Balmer lines from hydrogen (Fig. 27-22) in th8bo,jbhg n )o0e Sun. How fast is the star receding from us? v = C
