•How do we know that stars are millions of miles away? • How was the moon formed? • Is there life on planets that circle other stars? • What is a nova? • What are black holes?

You will find the answers in this book, and not in long, mind-numbing technicalities. Isaac Asimov’s unique skill and authority have never been better deployed than in this fantastic grand tour of the cosmos. Over the course of this brilliant expedition, the reader will experience close encounters with giant planets, unusual views of pulsating stars, and rendezvous with distant galaxies, as well as the unfolding history of astronomical discovery, beginning with Eratosthenes (who calculated the size of the Earth in 240 B.C.) and ending with the stunning scientific achievements of the present day. In no other book can the intelligent layman get so keen and thorough a summary of the riddles of Earth and space. Asimov deftly reveals the secrets of the universe with explanations that anyone from novice to scholar can understand and enjoy.

Puzzles by pulsars? Terrified by black holes? Bewildered by the big bang? Here are succinct, crystal-clear answers to more than one hundred of the most significant questions about planets, stars, galaxies, and the essential nature of the universe that have occupied astronomers since the beginning of history. For anyone who has ever looked up at the stars and wondered what it all means, Isaac Asimov’s Guide to Earth and Spaceis indispensible.

Here are some sample questions and answers from Asimov’s invaluable guide:

How was the moon formed?

By a collision in the first few hundred million years of planetary formation. An object roughly 10 percent of the Earth’s mass collided and coalesced with the Earth, causing a portion of the Earth’s rocky layer to erupt into space, which later developed into the moon. This theory was first proposed by William K. Hartmann in 1974. (See Chapter 43.)

Is the sun moving?

Yes, toward a location within the constellation Hercules. In 1805, William Herschel observed that stars seemed to be separating from one another on one side of the sky around a point inside the constellation Hercules and that they seemed to converge at another spot at the exact opposite side of the sky. He concluded from this that stars appear to be spreading apart as the sun approaches them, and that they seem to be moving together as the sun moves away. (See Chapter 78.)

What are black holes?

Incredibly dense neutron stars with masses 3.2 times greater than that of the sun. The gravity of such stars is so great that not even light can escape, a phenomenon which has caused them to collapse to a point of virtually no volume. It is an “infinitely deep ‘hole’ in space into which anything could fall but nothing could get out.” Black-hole theorist Stephen Hawking, by showing how black holes could “evaporate,” suggested that these objects were not absolutely permanent. (See Chapter 100.)

This is a series of 111 short, one- or two-page essays answering simple questions starting with the shape of the Earth and ending with the fate of the Universe. In this it rather resembles the earlier Please Explain. Here, however, since the book was written as a piece and not as a collection, the questions interact and each is related to the questions on either side, so there is a sense of gradually being drawn along. It’s a nice enough book—not world-shaking, but nice. My main gripe is that the cover of the hardback edition is absolutely bizarre—but there’s no accounting for taste, one supposes.