If you find that the H-alpha line in a star's spectrum occurs at a wavelength of 656.45 nm, what is the star's 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, meaning the star is moving away. The radial velocity can be calculated using the formula: v = c * (λ_observed - λ_rest) / λ_rest. Substituting the given values, v = 3 x 10^5 km/s * (656.45 nm - 656.30 nm) / 656.30 nm ≈ 70 km/s away.

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