There are many places in the sky in which there are dozens or hundreds of stars, or more, practically on top of each other. These are called clusters. Some clusters are very nearly symmetric; they are called globular clusters. Others have a more random, spread out appearance; they are the 'open' clusters. The open clusters are found only near the milky way region of the sky and are therefore also called 'galactic' (see below) clusters. The globular clusters are distributed more-or-less equally in all parts of the sky. It is attractive (irresistible, actually) to presume that the appearance of so many stars in almost exactly the same direction is no accident. That is all the stars in the cluster are actually near each other in space, not just coincidentally in the same direction as we see them. We will (later) presume that they have a common origin in time as well. (``Common origin in time'', in plain English, means ``same age''.)