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? Michael Rowan-Robinson answers these questions and encapsulates 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. His 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. Speculative ideas like inflation, 'Theories of Everything', strings and superstrings, are here but they are treated with a refreshing scepticism. Although most of what we know has been learnt during the twentieth century, Rowan- Robinson gives a historical perspective and pays homage to the achievements of the Greeks, renaissance astronomers and the age of Newton. He ends the book with a look forward in time, predicting that with the advent of the MAP and PLANCK- Surveyor space missions, the Large Hadron Collider and other planned experiments, all the nine numbers will be accurately known by 2015. But many questions and mysteries will remain and the book ends with the prediction that the origin of the Big Bang itself will remain a mystery in 2100 and perhaps even in the year 3000.