If astronauts could travel at v = 0.970c, we on Earth would say it takes (4.20 / 0.970)= 4.33 years to reach Alpha Centauri, 4.20 light years away. The astronauts disagree.
a) How much time passes on the astronauts' clocks?
b) What is the distance to Alpha Centauri as measured by the astronauts?