asterism

noun

Etymology: From Ancient Greek ἀστερισμός (asterismós, “a group of stars”), from ἀστήρ (astḗr, “star”). Analyzable as aster- + -ism.

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

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

   “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.”

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. A star-shaped figure exhibited by some crystals by reflected light (as in a star sapphire) or by transmitted light (as in some mica).