The constellations shown on modern star atlases are all officially approved by the International Astronomical Union, but while constellations are official, asterisms are not. An asterism is often defined as a noteworthy or striking pattern of stars within a constellation, but that is not always the case. The larger asterisms — ones like the Big Dipper in Ursa Major and the Great Square of Pegasus — are often better known than their host constellations.
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