Anyone who looks up at the starry sky at night and wonders how to find their way among all those stars will need some kind of sky-guide or atlas, but these must meet very different needs. The casual stargazer will first want to learn what can be seen with the unaided eye: the names of the stars, the constellations and where or when to look for Orion, the Great Bear, or Andromeda. The more advanced observer, with access to a good pair of binoculars or a small telescope, wants to know more: where is the Whirlpool Galaxy, the North America Nebula, or the globular cluster M13?

In 1991 – now twenty years ago – the first edition of The Cambridge Star Atlas (originally titled Cambridge Star Atlas 2000.0) was published, offering help for both. This twentieth-anniversary edition of The Cambridge Star Atlas includes a series of eight seasonal sky maps, designed to be of use for almost anywhere on Earth, and a series of twenty detailed star charts, covering the whole heavens, with all stars visible to the naked eye under good circumstances. These twenty star charts also show a wealth of star clusters, nebulae, and galaxies. Some of these can be seen without optical aids, but for most a small or average-size telescope is needed. Accompanying the charts are tables offering accurate positions and more details of these objects, as well as information about interesting double and variable stars.