This collection of essays from The Magazine of Fantasy and Science Fiction finds the eight-armed, four-typewritered Asimov venturing into the remotest crevices of light in the observable Universe and revealing that its diameter is 25,000 million light-years and will remain so until we invent an instrument that measures speeds faster than light. He also corrects Shakespeare's Caesar, who said, "I am as constant as the northern star." When Caesar lived "there wasn't any North Star/" -- Asimov's explanation is rather complicated but seems correct. Subjects covered include the stars, solar system, life, matter, energy, and numbers. He discusses the chemical inevitability of life on Earth, evolution, a short story he sold in which he predicted Everest would never be scaled because it was an observation post for Abominable Snowmen who were actually Martians (the story hit the stands five months after Everest had been climbed -- "Not one of my more luminous accomplishments!"), his abstention from alcohol, his thoughts on why the U.S. allowed its energy crisis to build, the largest prime number ever conceived, and much more. Each article is introduced with an amusing autobiographical anecdote. Ingratiating and mind-stretching when not boggling.