# Question: a spaceship is receding from earth at a speed of...

###### Question details

A spaceship is receding from Earth at a speed of 0.21c. A light
from the spaceship appears as yellow (**λ = 589.3nm**
) to an observer on earth. What would be its color as seen by the
passenger of the spaceship? (NOTE: Take into account the
relativistic effects, and then use the mathematics to solve)