Deep space

Solar system astronomy, which we described in the previous chapter, seems to encompass a vastness of space. The orbit of distant Pluto, after all, lies so far from our Earth that light reflected from the cold little planet's surface takes about five hours to reach us.

Nevertheless, the amateur deep-sky observer's Universe becomes so unimaginably large that the solar system shrinks to the status of a mere pinpoint within it. An ordinary backyard telescope can reveal galaxy clusters half a billion light-years distant, and may permit a glimpse of a quasar so remote in space (and in time) that its light has travelled several billion years to arrive at the Earth.

To the imaginative observer, deep-sky astronomy can be an awesome, even an unsettling, experience!

Deep-sky objects fall into two broad groups: features of our own Milky Way Galaxy and objects that lie elsewhere in the Universe, beyond our 100-billion-star local system. Perhaps surprisingly, scores of examples of even the very distant latter group are easily located with optical equipment no more sophisticated than good binoculars. The following chapters include a detailed catalogue of such objects.

Here, in brief summary, is a descriptive census of the deep-skyobject types that will be encountered by every amateur who explores the night sky with a telescope of any size.