Hogun's long sleep

A fun science fiction story for pre-teens. An alien named Hogun, who has been on Earth as an Observer for over two millennia, sleeps in his spaceship and wakes up every 243 years to monitor the progress of Earth's civilization. The last awakening takes place today: in the company of Xena, intelligent computer, he ventures outside the spaceship and meets Mark, a kid who is suspicious at first, but later becomes his friend. But will the adults be of the same opinion?