In Astronomy, what are asterisms?

Asterisms are star patterns which they do not form constellations on their own. An example is the Big Dipper, which is part of Ursa Major.

Asterisms range from simple shapes of just a few stars to more complex collections of many stars covering large portions of the sky. The stars themselves may be bright naked-eye objects or fainter, even telescopic, but they are generally all of a similar brightness to each other. The larger brighter asterisms are useful for people who are familiarizing themselves with the night sky.

Sometimes, they contain stars from more than one constellation: for example, the glorious Summer Triangle, is a very prominent in the northern hemisphere. It is made from the 3 brightest stars of Cygnus, Lyra and Aquila. In Sagittarius there is the famous “teapot” asterism, which points toward the center of our Milky Way galaxy. Pleiades is a popular asterism in Taurus; it is a lovely naked eye cluster of stars.

The constellations are very old, they are a link with our ancestors, a projection of their imagination in the cosmos, on the other hand, the asterisms are relatively new. There is nothing official about them, but many are well known. They are usually a simple pattern that is easy to recognize.