Suppose the wavelength of the 656.3-nm line in the hydrogen spectrum is shifted to 656.8 nm for light from a particular star.What can you deduce for the speed of the star relative to us?
A)914 km/s toward us
B)457 km/s toward us
C)914 km/s away from us
D)none of these answers
E)457 km/s away from us

Question

Quizplus · Accepted Answer

The wavelength of the light from the star is longer than the wavelength observed in the laboratory (656.8 nm vs. 656.3 nm), indicating a redshift. This redshift implies that the star is moving away from us. The speed can be calculated using the Doppler effect formula for light: $v = c \frac{\Delta \lambda}{\lambda}$, where $v$ is the velocity of the star relative to us, $c$ is the speed of light, $\Delta \lambda$ is the change in wavelength (656.8 nm - 656.3 nm = 0.5 nm), and $\lambda$ is the original wavelength (656.3 nm). Plugging in the values, we find that the speed corresponds to the option indicating the star is moving away from us at 457 km/s.

Suppose the Wavelength of the 656