constellations

Constellations are patterns of stars that form recognizable shapes in the night sky. They have been used since ancient times to identify regions of the heavens, to tell myths, and to aid navigation. In modern astronomy, a constellation is also a defined area of the celestial sphere with officially recognized boundaries. The International Astronomical Union (IAU) recognizes 88 constellations, which together cover the entire sky.

The idea of constellations predates written records and appears in many cultures. Classical sources such as Ptolemy's Almagest described a system of 48 between them. In the early 20th century the IAU formalized the list of 88 and, under the direction of Eugène Delporte, established precise boundaries in 1930. Most names are Latin or Greek, often reflecting mythological figures, animals, or objects commemorated by discoverers. Individual stars may be bright or faint and lie at vastly different distances; they are generally not physically related to one another in any single constellation.

Astronomers also use asterisms—informal patterns composed of stars from multiple constellations—such as the Big Dipper (part of Ursa Major). Constellations serve as a framework for locating celestial objects using coordinate systems like right ascension and declination, and they intersect the ecliptic, delineating the zodiac with twelve constellations along the Sun's apparent path.

The 88 constellations provide cultural and scientific utility, helping to organize observations, communicate positions, and study the structure of the night sky.