"Ever wonder how we know with any certainty that the first humans arrived in the Americas about 11,000 years ago? Or that dinosaurs died out about 65 million years ago? Or that the solar system is about 4.5 billion years old?...Hedman is worth reading because he is careful to present both the power and peril of trying to extract precise chronological data. These are all very active areas of study, and as you read Hedman you begin to see how researchers have to be both very careful and incredibly audacious, and how much of our understanding of ourselves—through history, through paleontology, through astronomy—depends on determining the age of everything."

Anthony Doerr | Boston Globe

"We are used to being told confidently of an enormous, measurable past: that some collection of dusty bones is tens of thousands of years old, or that astronomical bodies have an age of some billions. But how exactly do scientists come to know these things? That is the subject of this quite fascinating book, a collection of detective techniques that begins with the deciphering of Mayan hieroglyphs and the reconstruction of their extraordinary calendar, like a huge system of gears; and ends by tracing the universe back to its own birth. As told by Hedman, an astronomer, each story is a marvel of compressed exegesis that takes into account some of the most modern and intriguing hypotheses.... The book is dense with fact but beautifully lucid."

Steven Poole | The Gaurdian

"A concise, readable, and instructive work that succeeds in explaining a sampling of methods for measuring age and modern applications of their use."

Choice