The International Astronomical Union (IAU) divides the sky into 88 official constellations with precise boundaries, so that every direction belongs to exactly one constellation. These are mostly based upon the constellations of the ancient Greek tradition, passed down through the Middle Ages. The modern list is based on a list derived from the Romans,

In more recent times this list has been added to, both to fill gaps between Ptolemy's patterns (the Greeks considered the sky as including both constellations and dim spaces between, rather than composed of constellations as divisions) and also to fill up the previously hidden southern sky, as European explorers had journeyed to where they could see it.

Other proposed constellations didn't succeed in becoming recognised, most notably Quadrans Muralis (now part of Boötes) for which the Quadrantid meteors are named. Various other less official patterns have existed alongside the constellations called asterisms, and include:

• the Big Dipper in Ursa Major;
• the Plough and the Little Dipper in Ursa Minor;
• the Teapot in Sagittarius,
• Orion's belt;
• the Summer Triangle (Deneb, Altair, and Vega, or α Cygni, Aquilae, and Lyrae);
• the Great Square of Pegasus (which includes α Andromedae);
• the Urn in Aquarius;
• the Sickle in Leo.

Some ancient asterisms, for example Coma Berenices, Serpens, and portions of Argo Navis, are now officially constellations.

See also:

• List of constellations by area
• List of stars by constellation