asterism

plural asterisms

1. astronomyAn unofficial constellation (small group of stars that forms a visible pattern).

   The Big Dipper, Summer Triangle, and Orion's Belt are asterisms.

   2 more examples

   Of the constellations, or asterisms. [...] It therefore became necessary to adopt a more general method of distinguishing them. This was accomplished by portioning out the heavens into imaginary figures, of men, birds, fishes, &c. called Constellations or Asterisms.

   1825, Geo G. Carey, Astronomy, as it is known at the present day, London, p. 66 f

   Like Pisces and Capricorn, Aquarius is located in that part of the sky known as "Astral Sea," a region inhabited by water asterisms such as Eridanus, Cetus (the Whale), and the Dolphin.

   2007, Matilde Battistini, Rosanna M. Giammanco Frongia (translation from Italian into English), Astrology, Magic, and Alchemy in Art, page 60

2. A rarely used typographical symbol of three asterisks arranged in a triangle, ⁂, used to call attention to a passage or to separate subchapters in a book. Distinct from a dinkus which also uses asterisks to separate.
3. chemistryA star-shaped figure exhibited by some crystals by reflected light (as in a star sapphire) or by transmitted light (as in some mica).