Each constellation of stars in the night sky has a fascinating origin story. From the 48 constellations named by the Greek astronomer Ptolemy in his 2nd-century book The Almagest, to the dozens established by astronomers in the 16th and 17th centuries, their names reflect heroic tales from Greek myths, gods and goddesses, and various animals. Today, the International Astronomical Union recognizes 88 principal constellations in the northern and southern skies. Here’s how a few of them got their names.
Seven stars make up the hindquarters and tail of Ursa Major, the Great Bear, but you may know them better as the Big Dipper, named for the asterism's resemblance to a ladle or drinking gourd: Four of the stars appear to make a cup, and three extend outwards like a curved handle. The explanation for the larger constellation's ursine name is more complicated. In his book Metamorphosis, Ovid tells of how the huntress Callisto took a vow of chastity to the goddess Artemis, but Zeus, turning himself into Artemis’ likeness, tricked and seduced Callisto. She gave birth to their son, Arcas. When Zeus’ jealous wife Hera got wind of the affair, she turned Callisto into a bear. Years later, Arcas hunted the bear, not knowing it was his mother. To avoid further tragedy, Zeus turned Callisto into Ursa Major and Arcas into the constellation Boötes, the Herdsman.
Listed by Ptolemy in the Almagest, Cassiopeia is a constellation named for the infamously vain queen of Greek myth. Cassiopeia claimed that she was more beautiful than the sea nymphs known as Nereids, a bit of hubris that angered the sea god Poseidon. He sent a monster (recorded in the sky as the constellation Cetus, the Whale) to punish Cassiopeia and her husband, King Cepheus. They tried to appease the monster by offering him their daughter Andromeda (a legend with its own constellation). Cassiopeia is one of the most recognizable and visible constellations in the northern sky: Its five bright stars form a W shape, representing the queen seated on her throne.
Poor, virginal Andromeda had the misfortune of being the daughter of Queen Cassiopeia and King Cepheus. They chained her to a rock in the sea as a sacrifice to the monster Cetus. Things looked bleak for the beautiful Andromeda until Perseus, a demigod hero who had just slain the gorgon Medusa, swooped down from the heavens and rescued her in one of the most romantic scenes in Greek mythology.
The constellation Andromeda once shared its main star, Alpha Andromedae (sometimes called Alpheratz), with the neighboring constellation Pegasus. The spiral galaxy M31, also called the Andromeda Galaxy because it lies within the star group, is 2.5 million light-years from Earth and the farthest thing in space visible to the naked eye.
Pegasus, the winged horse of Greek legend, has quite the origin story. After Perseus slayed Medusa by cutting off her head, Pegasus sprang from her bloody neck and flew off. Some say Perseus was actually riding Pegasus when he rescued Andromeda, but in myth the horse is more closely associated with the hero Bellerophon. Zeus also employed Pegasus in carrying his thunderbolts. Though the constellation depicts only the front half of the horse, Pegasus is the seventh-largest group of stars in the northern sky. In Ptolemy’s time, the body was formed by the “square of Pegasus,” a group of four bright stars — but since then, the star near Pegasus’ navel was given to the adjacent constellation Andromeda as Alpha Andromedae, leaving just three stars in the well-known square.
The famous celestial Hunter is easy to spot in the night sky thanks to the three closely spaced stars of his belt, as well as the bright stars Betelgeuse and Rigel at his right shoulder and left foot. The constellation Orion faces Taurus, the Bull — suggesting that Orion may be based on the Sumerian hero Gilgamesh or the Greek hero Heracles, both of whom fight bulls. Orion’s many legends and stories feature his prowess as a brave hunter, but his death came about because of his pride. In one version of the tale, Orion boasted that he could kill any beast on Earth, which offended the Earth. (In another version, Orion’s boast offended Artemis, the goddess of hunting.) The Earth opened to send forth a scorpion, which fatally stung Orion. As a result, the constellations Orion and Scorpio are at opposite ends of the sky so it appears that Orion is fleeing the sky as the scorpion rises in the east.
Ptolemy identified Hydra, the Water Snake, as one of the longest constellations in the Southern Hemisphere, as well as the largest. In Greek myth, Hydra is a fearsome water serpent with multiple heads, one of which is immortal. (Five stars at one end of the linear constellation represent the heads of the snake.) The hero Heracles was tasked with killing Hydra as the second of his 12 labors, but every time Heracles cut off one of the monster’s heads, two more grew in its place. Heracles’ nephew Iolaus suggested they burn the necks after cutting them off to prevent them from regenerating. They eventually slayed the beast by burying its remaining immortal noggin under a rock. Heracles then dipped the points of his arrows in Hydra’s blood to render them lethal.
According to Greek mythology, centaurs were half-horse, half-human creatures with a bad reputation as rowdy drunkards, but the centaur Chiron was an exception. The wise Chiron taught medicine and music, and his pupils included Greek heroes like Achilles and Jason. Chiron was mortally wounded when Heracles accidentally shot him with an arrow — one that he had dipped in Hydra’s blood to make its strike fatal. But because Chiron was immortal, he couldn’t die from his injury. Zeus took pity on Chiron and released him to the sky, where he became the constellation Centaurus.
Centaurus is home to Alpha Centauri, the star system closest to our sun and solar system, which appears as one of Centaurus’ hooves. Alpha Centauri and another star called Beta Centauri are near the constellation Crux, the Southern Cross; in Ptolemy’s era, Crux was part of Centaurus’ rump.
Monoceros means “one-horned” in Latin, so it’s an appropriate name for the Unicorn constellation. This group was first shown on a globe by the Dutch astronomer and theologian Petrus Plancius in 1612. The Unicorn fills a part of the sky between the constellations Hydra, Orion, Canis Major, and Canis Minor, all of which Ptolemy listed in the Almagest. According to science writer Ian Ridpath, Plancius may have fashioned the Unicorn after the famous Hunt of the Unicorn tapestries woven in the Netherlands around 1500. One tapestry shows the unicorn pursued by hunting dogs; Monoceros is positioned in the sky between Canis Major and Canis Minor, the two celestial dogs.
Navigators Pieter Dirkszoon Keyser and Frederick de Houtman accompanied the first Dutch voyage to what is now Indonesia in 1595. Petrus Plancius had trained and instructed Keyser to chart stars in the Southern Hemisphere, and de Houtman served as Keyser’s assistant. They eventually identified 12 new southern constellations and named some after the natural history of the region. The Phoenix, located near the constellation Eridanus, refers to the mythical, multicolored bird that is able to rise from the ashes of its predecessor. The Dutch duo may have been inspired to record the Phoenix after seeing birds of paradise, a group of spectacularly plumed birds native to Indonesia and first described by Europeans in the 16th century. Ankaa, the Arabic name of the constellation’s largest star, means phoenix.
When Heracles was made temporarily insane by the goddess Hera, he killed his wife and children. To atone for the murders, he was assigned 12 seemingly impossible labors. The first: to kill the Nemean lion, a fearsome beast with an impervious hide that relished attacking the local villagers. Heracles succeeded in overcoming the lion by gripping him in a bear hug and squeezing him to death. The constellation Leo echoes the lion’s ferocious attitude: A group of six stars are arranged in an arc representing the animal’s front torso and head, preparing to pounce. The brightest star in the arc is named Regulus, meaning “little king.”
Vulpecula, the Fox, is sometimes called Vulpecula cum Anser, or the Fox with a Goose, because the celestial canine was thought to have the bird in its mouth. The Polish astronomer Johannes Hevelius invented the scene as one of 10 new constellations in his star catalog and atlas, which he published in 1690. Hevelius placed Vulpecula — a collection of faint stars that doesn’t look much like a fox or a goose — near two other Northern Hemisphere constellations of notorious animals, Aquila (the Eagle, named by Ptolemy) and Vultur Cadens (the Vulture), the Roman name for the constellation Lyra. Vulpecula is home to the Dumbbell Nebula, an outburst of gases and dust from a dying star that resembles a barbell at the gym.
Keyser and De Houtman’s constellation Tucana, the Toucan, got its name from a possible case of mistaken identity. In 1597, De Houtman had called the constellation Den Indiaenschen Exster, op Indies Lang ghenaemt (“the Indian magpie, named Lang in the Indies”), which referred to its long bill. De Houtman was most likely describing a hornbill, birds with oversized, toucan-like bills, native to Asia. But when Petrus Plancius published Keyser and De Houtman’s 12 new constellations in 1603, he called this one Tucana, the Toucan, for birds native to South America. Ian Ridpath suggests that Keyser, who had traveled to South America and may have seen toucans there, named the constellation before he died in 1596 on the East Indies voyage. Tucana boasts two celestial phenomena of note: the extremely bright globular star cluster 47 Tucanae and the Small Magellanic Cloud, a dwarf galaxy near the Milky Way.