Suppose the laboratory wavelength of a spectral line is 600 nm. In a star it is measured to be 599.4 nm. Is the star moving toward or away from us, relative to the line of sight How fast is it moving (Hint: c = 300,000 km/s)
A)toward; 300 km/s
B)away; 300 km/s
C)at rest; 0 km/s
D)sideways; 300 km/s
E)toward; 150 km/s

Question

Quizplus · Accepted Answer

The star is moving toward us because the observed wavelength (599.4 nm) is shorter than the laboratory wavelength (600 nm), indicating a blueshift. The speed can be calculated using the Doppler shift formula: $v = \frac{\Delta \lambda}{\lambda} \times c = \frac{600 - 599.4}{600} \times 300,000 \, \text{km/s} = 300 \, \text{km/s}$.

Suppose the Laboratory Wavelength of a Spectral Line Is 600