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The International Astronomical Union divided the celestial sphere into 88 constellations in 1922, with the help of Henry Norris Russell, an American astronomer.
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Constellations are groups of stars in the sky, which have been grouped together to form patterns representing the history of mankind, including animals, mythological characters, and objects.
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48 of the 88 constellations officially recognized by the International Astronomical Union were recorded in 150 AD by Ptolemy, a Greek astronomer. He recorded the constellations in his book Almagest.
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In addition to Ptolemy's original 48 constellations, 40 more were later added by explorers and astronomers, including Gerardus Mercator (Dutch explorer in the 1500s), Pieter Keyser and Frederick de Hautmann (turn of 16th century). Johannes Hevelius (1690), and Nicolas Louis de Lacaille (French astronomer in 1750s).
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In the 8th century BC Homer wrote about Orion, Bootes, and Ursa Major in his poem Illiad and the Odyssey. This was the first Greek reference to constellations, which would have been learned from the ancient Egyptians.
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Constellations travel from the east to the west, beginning at dusk in the east and ending at dawn in the west.
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Constellations are sometimes grouped into families. These constellations are located in the same area of the sky and the family name comes from the most prominent constellation in that area.
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The Hercules Family contains 19 constellations; the Ursa Major Family contains 10 constellations; the Perseus Family contains 9 constellations; and the Orion Family contains 5 constellations.
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Some of the most famous constellations include Orion, Ursa Major, Ursa Minor, the Zodiac, and Pegasus.
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Many people believe that the Big Dipper and the Little Dipper are constellations but they are actually asterisms, patterns contained within constellations. The Big dipper is an asterism within Ursa Major for example.
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The brightest constellation is Crux, also known as the Southern Cross, and the largest constellation is Hydra which covers 3.158% of the night sky.
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There are 13 zodiac constellations including Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, and Ophiuchus. The first 12 are also used for astrology and the zodiac calendar.
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Some of the constellations in the southern hemisphere include Grus (crane), Hydrus (water snake), Lepus (rabbit), Musca (fly), Pavo (peacock), Tucana (toucan), Dorado (swordfish), Chamaeleon (chameleon), and Apus (bird of paradise).
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Some of the constellations in the northern hemisphere include Andromeda (princess), Aquila (eagle), Bootes (herdman), Canis Major (big dog), Canis Minor (little dog), Draco (dragon), Lyra (harp), Orion (hunter), Perseus (Medusa's killer), Ursa Major (big bear), Ursa Minor (little bear), and Vulpecula (little fox).
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