The constellations, which reflect mankind's earliest efforts to attach representative significance to what was seen in the night sky, were physically formed at the same time as the billions of other stars, but began to be named according to the patterns seen in their respective groupings around 2000 B.C. Scorpio the scorpion and Leo the lion are two of the earliest known names given to star groups. The Greeks began to name and document constellations in earnest beginning around 500 B.C.
The formalized naming of the patterns seen in star groupings began as a means of discerning heavenly interactions between the gods and humankind. These representations varied between different cultures and reflected each culture's specific theological belief system. It was eventually discovered that the positions of various star groups, or constellations as they came to be called, could also aid in navigation and geographic orientation. The 2nd-century A.D. Greek-Egyptian astronomer and mathematician, Ptolemy, was the author of what is considered the first astronomical star catalog, the Almagest, which named 48 constellations containing the positions of more than 1,000 stars. Ptolemy's star catalog remained in use for the next 1,400 years.
Between 700 and 1600 A.D., the Arab astronomers added to the listings, with newly-named stars, such as Betelgeuse and Aldebaran, reflecting Arabic roots in their name origins. From 1600 to the 20th century, many new constellations were added to the existing star catalogs, and elaborate astronomical and astrological atlases were printed.
In 1919, the International Astronomical Union was created to safeguard and promote the science of astronomy. In 1930, the IAU established internationally accepted boundaries for the 88 constellations which can be seen across the entirety of the celestial sphere.