 During that time, he would see the Earth twin in the image grow older by .He then sees high frequency (blue) images during the back trip of 3 years.During that time, he would see the Earth twin in the image grow older by When the journey is finished, the image of the Earth twin has aged by 

The Earth twin sees 9 years of slow (red) images of the ship twin, during which the ship twin ages (in the image) by He then sees fast (blue) images for the remaining 1 year until the ship returns.