This app shows the effect of time dilation in relativity. Rocket travels to the planet far from Earth. The distance from Earth to the planet could be changed from 1 light-year to 100 light-years. Rocket speed could be changed from 0.01c to 0.99c. Time on rocket means time spent for rocket to reach the planet, which is measured on the rocket. Time on Earth means time spent for rocket to reach the planet, which is measured on Earth. c is the speed of light. The first plus button increases distance by 1 light-year. The second plus button increases rocket speed by 0.01c.