me: layman's understanding of physics and mathmatics My (very basic) understanding for this question is that: a higher rate of (objective) motion = lower rate of time for anything with mass. Is there a working figure for how much motion we experience per a specific time period from such sources as the motion of the local galatic cluster, the rotation of the galaxy, the motion of our star, the spin of the earth, etc.? Whatever that figure might be, are we experiencing any time dilation effect in relation to the universe at-large? Lastly, for the purposes of figuring your speed as a percentage of the speed of light, at what point do you begin counting? For example: If my star is moving at 100,000 miles per hour and I launch my spaceship in the same direction going 20,000 mph and shoot myself out the tip of my craft at 100 mph, at what speed am I going in relation to achieving the speed of light? 120,100? 100? Or do I need to start at rest and develope my own motion? Thank you.