In the twins paradox of relativity one twin stays on earth while the other travels to a star ten light years away, and then immediately flies back. Because his rocket travels at just under the speed of light, the entire (including the return) journey takes just under twenty years as measured by clocks on earth, but only a day, say, according to the clocks on the rocket. Furthermore, the twin on earth has physically aged by twenty years, while the traveling twin has aged only a day.
If the clocks at the distant star are synchronized with those on earth, (Einstein synchronized, if that helps, which just means that looking at across the ten light year gap, each would see ten year old light indicating a time that was ten years less than one's own clock shows, a symmetrical situation) what do they say the time is when the twin arrives there and what do the clocks on the rocket say?
Note, "paradox" might be a bit of a misnomer, as it's really just counterintuitive.