Constellations and asterisms
A constellation is a defined region of the sky. A star pattern is a different way of reading the same sky.
A map of 88 regions
The astronomical catalogue divides the whole celestial sphere into 88 constellations. A constellation includes the sky inside its boundary, rather than only the bright stars used to draw a familiar figure.
This distinction matters when naming a star or describing an object’s position. An object can belong to a constellation even when it does not appear in the constellation’s line pattern.
Patterns help us recognise the sky
An asterism is a recognisable arrangement of stars. It may sit within one constellation or extend across several. It does not need a formally defined boundary.
The green lines on these charts provide a visual pattern. They are separate from the region boundary, and other charts may join the same stars in a different way. Stars that look close together on a map can lie at very different distances from Earth.
One constellation with two parts
Serpens is divided into Serpens Caput, the head, and Serpens Cauda, the tail. These are two separate areas with their own charts and boundary files. They count as one constellation, so this atlas has 88 catalogue entries and 89 chart sections.
Names, abbreviations and genitives
Each entry has a Latin name, a three-letter abbreviation and a common name. The abbreviation is a compact identifier. The Latin genitive is a grammatical form used when naming stars; for example, Alpha Orionis refers to a star in Orion.
The catalogue keeps these fields separate, making it possible to search by a name you recognise and still find the same constellation.
Different cultures, different sky patterns
The 88-region catalogue is a shared astronomical reference. It does not describe every cultural tradition of naming or grouping stars. Historical and living sky traditions may use different figures, names and groupings.