How old is the universe? How far away are the galaxies and how fast are they travelling away from us? What do the atoms in our bodies, our very existence, tell us about the history of the universe? Are we in a special place in the universe? What is dark matter and why do astronomers think it pervades the universe? How heavy is the vacuum? How do galaxies form? This volume aims to answer these questions and encapsulate all that modern astronomy has learnt about the universe around nine numbers. Some, like the age of the universe are natural choices. Others are less obvious. The author's motto is Montaigne's What do I know and the reader emerges with a genuine feel for what we really know about the universe and also what we do not know. Only one of the nine numbers is known with real precision and four of them are extremely poorly known. Difficult ideas like the origin of the elements, the general theory of relativity, quantum theory, and the standard model of particle physics, ideas which underpin modern cosmology, are explained in a simple way. This book is intended for general readers of popular science.