Origins for the earliest constellations likely goes back to prehistory, whose now unknown creators collectively used them to related important stories of either their beliefs, experiences, creation or mythology. As such, different cultures and countries often adopted their own set of constellations outlines, some that persisted into the early 20th Century. Adoption of numerous constellations have significantly changed throughout the centuries. Many have varied in size or shape, while some became popular then dropped into obscurity. Others were traditionally used only by various cultures or single nations.
The Western-traditional constellations are the forty-eight Greek classical patterns, as stated in both Aratus' work Phenomena or Ptolemy's Almagest — though their existence probably predates these constellation names by several centuries. Newer constellations in the far southern sky were added much later during the 15th to mid-18th century, when European explorers began travelling to the southern hemisphere. Twelve important constellations are assigned to the zodiac, where the Sun, Moon, and planets all follow the ecliptic. The origins of the zodiac probably date back into prehistory, whose astrological divisions became prominent around 400BCE within Babylonian or Chaldean astronomy.
In 1928, the International Astronomical Union (IAU) ratified and recognized 88 modern constellations, with contiguous boundaries defined by right ascension and declination. Therefore, any given point in a celestial coordinate system lies in one of the modern constellations. Some astronomical naming systems give the constellation where a given celestial object is found along with a designation in order to convey an approximate idea of its location in the sky. e.g. The Flamsteed designation for bright stars consists of a number and the genitive form of the constellation name.
Another type of smaller popular patterns or groupings of stars are called asterisms, and differ from the modern or former constellations by being areas with identifiable shapes or features that can be used by novice observers learning to navigate the night sky. Such asterisms often refer to several stars within a constellation or may share boundaries with several constellations. Examples of asterisms include: The Pleiades and The Hyades within the constellation of Taurus, the False Cross crossing the southern constellations of both Carina and Vela, or Venus' Mirror in the constellation of Orion.
The word "constellation" seems to come from the Late Latin term cnstellti, which can be translated as "set of stars", and came into use in English during the 14th century. The Ancient Greek word for constellation was Greek letters used in mathematics. A more modern astronomical sense of the term "constellation" is simply as a recognisable pattern of stars whose appearance is associated with mythological characters or creatures, or earthbound animals, or objects. It may also specifically denote the officially recognised 88 named constellations used today.