 Then the ship turns back toward home.The clock of the staying twin shows "1 year after launch" in the screen of the ship, and during the 3 years of the trip back it increases up to "10 years after launch", so the clock in the screen seems to be advancing 3 times faster than usual.When the source is moving towards the observer, the observed frequency is higher ("blue-shifted") and given by
This is "f"obs = 3"f"rest for "v"/"c" = 0.8.