Well, if you are serious about that, then Billions & Billions is excellent, but let me urge you to hold off and purchase an even better one by Sagan. The Demon Haunted World: Science As A Candle In The Dark is similar in the sense that it is a compilation of Carl Sagan's essays. However, there is an underlying theme of discussing the past and modern "unknowns" of the world, how humans interpretted them (with myth) and how science has shone light on them. His essays then get into more modern things, such as UFO sightings, ghosts, etc. and what science has to say about them.

In this book, Sagan not only uses cut-throat science to debunk myths, he does what a lot of debunkers fall short on. He replaces these exciting but unlikely myths with truly exciting modern science that doesn't make one have want or need of previous, yet wrong beliefs. Most just debunk, and then leave it at that, and I think that's wrong. There is so much awesome scientific questions we don't have answers to, it's very stimulating to point them out and pose possible paths to new discovery.

This book, I have to firmly say, is my favorite non-fiction science piece that I have in my collection (and it's a very large collection). I have read it at least four times all the way through, and have often re-read other select parts more than that. If I were stranded on a desert island and could only bring, say five books with me, I don't know what all five would be, but The Satanic Bible and The Demon Haunted world would make the cut!
"Extraordinary claims require extraordinary evidence."
-Carl Sagan