WHAT IS A YEAR?

Were you to board a spaceship, head out from earth at 99.999999 percent of light speed, travel for six months and then head back home at the same speed, your motion would slow your clock, relative to those that remain stationary on earth, so that you'd be one year older upon your return — while everyone on earth would have aged about 7,000 years. Or, were you to venture into space again and spend a year hovering a dozen feet above the edge of a black hole, whose mass was 1,000 times that of the sun, the strong gravitational field would slow your clock so much that on your return to earth, you'd find that more than a million years had elapsed...
NYT