1. The problem statement, all variables and given/known data Alpha Centauri, the closest star to Earth, is 4.3x10^6 m away. How long would it take a spaceship to reach the star if it were travelling at 0.999c? 2. Relevant equations I did get the answer as 0.2a....and the textbook also said it would take about 2 months, I do not understand what the a represents/stands for and how the textbook got 2 months from 2a. Also, I do not why I had to find tm and then to? 3. The attempt at a solution ts = d/v = 4.3 x 10^16/0.999c = 1.43x10^8 s tm = ts/√(1-v^2/c^2 = 1.43x10^8/√(1-(0.999c)^2/c^2 = 3.19 x 10^9 s tm = 4.5a THE ANSWER KEy gets the same answer till the part above but then the answer key starts doing more calculations afterwards(below) which I do not get ts = tm√1-v^2/c^2 = 4.5a√1-(0.999c)^2/c^2 ts = 0.2a the textbook gave 0.2a but also said it will take two months to reach the star and that is what I do not understand. Thanks for your help.