They are often just thick enough to blot out only the faint stars in Cancer but leave the brighter stars of other constellations shining brightly. Amateur astronomers often use the Crab in this way. When it disappears, stargazers know it is time to quickly load the scopes in the car and head for home. Before they do, they usually try to take a look at the Praesepe, or Beehive, a cluster of stars visible to the naked eye from dark rural skies as a faint, fuzzy patch of light. It is just to the left of the eyes of the crab, and is marked as M44 on the accompanying star chart.
Most clusters of stars are relatively young.
In long exposure photos, we see remnants of the hydrogen gas and dust out of which the stars formed. Such a cluster is the Pleiades, setting now in the western sky. Eventually, the gas and dust disperses, and the stars in the cluster slowly drift apart. If our own star, the Sun, formed in a cluster of stars, for example, there is no sign that we are still embedded in a cluster. The Beehive is the rarer exception.