We are all so familiar with the appearance of the Moon up there in the sky that we usually forget just what it is - a completely separate world, orbiting Earth, out there in space. For thousands of years people stared up at its unchanging face, going through its phases, growing from crescent to full Moon and then shrinking again till about a month later it was back to a crescent in the evening sky again.

But 400 years ago, everything changed. A man in Isleworth near London gazed at it through the newly invented telescope, and made the very first sketch of the Moon. That man was Thomas Harriot, and 2009 marks the anniversary of his historic observation.

Today, of course, men have visited the Moon and there are plans to return there. We know that the Moon is our natural satellite, an airless world of craters and mountains. It orbits the Earth every month or so, and the Sun’s changing illumination gives rise to the phases.

On these pages we hope you will find virtually everything you need to know about the Moon, from observing it using nothing more than your eye or binoculars, to details of the Apollo missions that gripped the world back in the 1970s. And there are answers to some of those knotty questions – why does the Moon look larger when it’s close to the horizon? When is the Moon actually blue? Do people really go mad by looking at the full Moon? Use the chapter headings at left to find main topics of interest, and those on the right for more details within each chapter.

Oblique view of the lunar surface from Apollo 15