Asterisms are random clusters of stars of the same or different brightness, which physically do not belong together, but just happen to be in the same direction. According
to this definition also the 88 constellations can be called asterisms. The well known ones are certainly the "Big Dipper", the "Southern Cross" or the constellation "Orion"
in the winter sky.
The distance between the stars of an asterism can be many thousands of light years, although the impression in the eyepiece is different and suggests a non-existing proximity.
This is also the biggest difference to the so called "open star clusters", where the stars are actually all very close and therefore gravitationally bound to each other - completely
in contrast to the stars of an asterism.
Asterisms are characterized in many cases by particularly memorable star patterns and shapes. Some objects are very simply composed of only a few stars, while others consist
of many stars and are quite complex. A very well known asterism is the "coat hanger" in the constellation "Vulpecula" - an object which can be seen in the summer sky and is
already a great sight in binoculars.
