This is one of those books that's been on my bookshelves for years. I've read it before, and every so often I dip back into bits of it - admittedly, often to look at the huge range of startlingly beautiful illustrations, many of which are astronomy glamour shots. But I've just reread the entire thing again, so it's time to add it here.

Sagan was an excellent science communicator. His explanations of what we know about the different planets, and how we know it, are clear and interesting (if, at this point, a little behind the times). In some ways, though, those explanations feel like a lengthy introduction to the real meat of the book: space exploration, and how (if) we do it. Sagan's clearly for it, but he doesn't shy away from the validity of the arguments against. As he says, with so many problems on Earth, and a limited budget, hard choices need to be made and sometimes space exploration will (and should) be the loser. Yet he also argues for aspiration and scale, for individuals and nations working together, each contributing a little of the whole needed, focusing primarily on robotic missions for a long while. Putting humans into space is a long term goal, of course, but it's far more expensive, and often less effective, at getting scientific results when compared to the purely mechanical. That said, human colonisation of space is fundamentally a necessity in order to preserve the species (howsoever it may evolve), and his imaginings of what could be done, in the generations to come, make me hope he's right.

It's just a beautifully put together book.