I read this book in 1979 while in the fourth grade and, to this day, it is still one of my favorites. I can't count the number of times I have read it. Though written for children, it is a great adventure story that any adult would appreciate. Ms. Jansson has a delightful way with words and character development.
When Moomintroll learns that a comet will be passing by, he and his friend Sniff travel to the Observatory on the Lonely Mountains to consult the Professors. Along the way, they have many adventures, but the greatest adventure of all awaits them when they learn that the comet is headed straight for their beloved Moominvalley.