One of Albert Einstein's greatest insights was realizing that time is relative. It speeds up or slows down depending on how fast one thing is moving relative to something else. How much does it change? In this feature originally designed for students in 1996, "Captain Ein" and "Major Stein" have volunteered to help you find out. Send Captain Ein on a round-trip journey to a star and then compare her age with Major Stein's on Earth.—Jenny Lisle