Pleiades open star cluster, M45
A constellation is a group of stars that are considered to form imaginary outlines or meaningful patterns on the celestial sphere, typically representing animals, mythological people or gods, mythological creatures, or manufactured devices. The 88 modern constellations are formally defined regions of the sky together covering the entire celestial sphere.
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’s 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.
Image Credit: NASA, ISS Expedition 40, Reid Wiseman
The nebula, located 20,000 light-years away in the constellation Carina, contains a central cluster of huge, hot stars, called NGC 3603.
Image credit: NASA/ESA/Hubble
Venus, Mars, Spica and a Meteor Caught;
The Pleiades, Hyades and Orion.
Composed of gas and dust, the pictured pillar resides in a tempestuous stellar nursery called the Carina Nebula, located 7500 light-years away in the southern constellation of Carina.
Credit: NASA, ESA and the Hubble SM4 ERO Team
Outbursts of a newborn star in the orion constellation
Credit: ESO/M. McCaughrean