星座是指天上一群群的恒星组合。自从古代以来，人类便把三五成群的恒星与他们神话中的人物或器具联系起来，称之为“星座”。星座几乎是所有文明中确定天空方位的手段，在航海领域应用颇广。对星座的划分完全是人为的，不同的文明对于其划分和命名都不尽相同。星座一直没有统一规定的精确边界，直到1930年，国际天文学联合会为了统一繁杂的星座划分，用精确的边界把天空分为八十八个正式的星座，使天空多数恒星都属于某一特定星座。这些正式的星座大多都以中世纪传下来的古希腊传统星座为基础。与此相对地，有一些广泛流传但是没有被认可为正式星座的星星的组合叫做星群，例如北斗七星（参见恒星统称列表）。

In everyday usage, a constellation is a traditional or recognizable group of stars in the night sky, or the region of the sky containing them. In technical usage these meanings have been separated, with groupings of stars being called asterisms, and the word constellation being reserved for a specific area of the celestial sphere with boundaries laid down by the International Astronomical Union (IAU). These areas mostly had their origins in Western-traditional asterisms from which the constellations take their names. When astronomers say something is “in” a given constellation they mean it is within those official boundaries. There are 88 officially recognized constellations, covering the entire sky which have grown from the 48 classical Greek constellations laid down by Ptolemy in the Almagest.