CodBall

Hi all, 23 year old here new to the forum after watching an episode about Time on "Through the Wormhole" I couldn't quite bend my head around the concepts in the video and thought perhaps some of you could help out, I only hold a GCSE in Physics but I'm constantly intruiged and amazed with the field and find myself watching and reading things about it. My question is as follows: Understanding that time is relative to the speed of an object or the gravity surrounding an object and that time will appear normal to an observer stood in the moment looking at his surroundings even on the event horizon of a black hole, the documentary said that if a spaceship were to travel at the speed of light to a planet say 10 light years away and back, that when the ship returned the crew would have experienced for 20 light years of time however during that time Earth would have experienced a thousand years. But...if the speed is constant and the distance remains the same when the spaceship arrives back at Earth won't they both have experienced (and aged) 20 years? I guess from the perspective of Earth it would look like the ship is taking longer to get to the planet but on it's way back the trip would only look as if it takes half as long, would that be right? Excuse if it's a stupid question, just something I'm trying to wrap my head around.