Question

(a) How fast and in what direction must galaxy A be moving if an absorption line found at 550 nm (green) for a stationary galaxy is shifted to 450 nm (blue) for A? (b) How fast and in what direction is galaxy B moving if it shows the same line shifted to 700 nm (red)?

Answer 1

Explanation:

For Part (a)

Since the apparent wavelength decreases hence galaxy moving towards the stationary observer.

Δλ/λ=v/c

$=\frac{v}{c}\\ v=\frac{550-450}{550}*3*10^{8}\\ v=5.4545*10^{7}m/s$

For Part (b)

Since the apparent wavelength increases hence galaxy moving towards the stationary observer.

Δλ/λ=v/c

$=\frac{v}{c}\\ v=\frac{700-550}{550}*3*10^{8}\\ v=8.1818*10^{7}m/s$