If you find that the hydrogen alpha line in a star's spectrum occurs at a wavelength of 656.45 nm, what is the star's approximate radial velocity? Note that the rest wavelength of this line is 656.30 nm.
A) 150 km/s away from you
B) 150 km/s toward you
C) 350 km/s toward you
D) 70 km/s away from you
E) 70 km/s toward you

Question

Quizplus · Accepted Answer

The observed wavelength is longer than the rest wavelength, indicating a redshift. This means the star is moving away. Using the formula for radial velocity: v = c * (observed - rest) / rest, where c is the speed of light (300,000 km/s), the velocity is approximately 70 km/s away.

If You Find That the Hydrogen Alpha Line in a Star's