Carl Sagan has written lots of books, and he was one of the grand
old men of the US space program. He has taken part in most of the
US space missions, albeit he never got to fly himself. Among other
things, he's the person responsible for the plaque that was sent
into space 1972 on board of Pioneer 10 and bears a message about
our small blue planet and its inhabitants.
Here's a picture of the plaque.
This book is a call for space exploration and the search for extraterrestrial life. It describes the solar system, one planet per chapter, including weather reports and possible uses for humans who might want to set foot on them. Since it's almost clear now that none of these near bodies contains intelligent life, Sagan discusses life beyond the solar system - either other beings, or our own life, once we expand across the stars.
The book, although sometimes passionate in its call to fire up the rockets, shows that Sagan knew a lot of what has been said against space travel in general, against manned spaceflight in particular, against SETI (Search for Extraterrestrial Intelligence) and so on. He discusses them and calmly advocates that - I quote from the back cover: "The exploration and eventual settlement of other worlds is neither a fantasy nor a luxury [...] but rather a necessary condition for the survival of the human race."
I recommend this book to every wannabe space traveller. It is very refreshing to see that even someone old and wise, someone who knew so much of the space administration and politics kept his faith in the human future in space. I regret having bought the cheapest edition without pictures because Sagan spends some paragraphs discussing images sent back to Earth by planetary probes. I had to pay dearly and buy the NASA Atlas of the Solar System later :-)