Question

Light from the constellation Virgo is observed to increase in wavelength by 0.4%. With respect to Earth the constellation is

• A. Moving away with velocity $1.2 \times 10^{6}m/s$
• B. Coming closer with velocity $1.2 \times 10^{6}m/s$
• C. Moving away with velocity $4 \times 10^{6}m/s$
• D. Coming closer with velocity $4 \times 10^{6}m/s$

Answer 1

Answer: (A)

Moving away with velocity $1.2 \times 10^{6}m/s$

Answer 2

By using $\frac{\Delta\lambda}{\lambda} = \frac{v}{c};$ where $\frac{\Delta\lambda}{\lambda} = \frac{0.4}{100}$ and c = 3 × 10⁸ m/s

⇒ $\frac{0.4}{100} = \frac{v}{3 \times 10^{8}}$ ⇒ v = 1.2 × 10⁶ m/s

Since wavelength is increasing i.e. it is moving away.