Glossary term: Asterism

Description: Most of the bright stars in the night sky have been grouped into patterns called constellations. But in addition to the official constellations, which were defined by the International Astronomical Union, there are also groupings of stars that form patterns called asterisms. Perhaps the best-known asterism is the Big Dipper – a group of stars that is part of the larger constellation Ursa Major.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

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A steaming pool of water with the night sky. The sky shows a bright group of 7 stars in the shape of a pan and handle

The Big Dipper in Yellowstone, by Alex Conu, Norway

Caption: First place in the 2021 IAU OAE Astrophotography Contest, category Wide star fields. This image shows one of the most prominent and well-known asterisms of the Northern Hemisphere – the Big Dipper or the Plough. This asterism is part of the constellation from Greek mythology – Ursa Major (the Great Bear). The Big Dipper comprises seven (eight) stars extending from the center to the right of the image. The four stars that form the “cup” of the dipper are in the shape of a trapezium just above the tallest tree towards the right of the image. These stars are Dubhe (top right), Merak (bottom right), Megrez (top left) and Phecda (bottom right). The three (four) stars that form the handle are to the left to trapezium (from right to left: Alioth, Mizar and Alkaid). Looking closely at Mizar, it is possible to see a smaller star to the top left and “touching” Mizar. This is Alcor, and with Mizar they make up the unaided-eye double-star system. However, very careful measurements have provided evidence that Mizar is in fact a quadruple system, and Alcor is a binary system. Although the names of the stars are derived from the Arabic names for the stars, different cultures have their own names for the stars. In various cultures around the world, this asterism is associated with different objects, and furthermore, some indigenous cultures associate stories with individual stars. Constellations in addition to encompassing stories and myths of various cultures, are important navigation “tools”. The stars Dubhe and Merak, can be used to find the Pole (North) Star – Polaris (not seen in this image). Given its relationship to the Northern Hemisphere and being a circumpolar constellation (never setting below the horizon), the Big Dipper and Polaris are used on the flag of Alaska. It is important to note that although the stars (except for the multiple star systems of Mizar and Alcor) in constellations appear to be “next” to each other, in reality the stars are at various distances from Earth and from each other.
Credit: Alex Conu/IAU OAE

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The ladle-shaped Big Dipper tilted by 135 degrees.

Big Dipper

Caption: Honourable mention in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   This photograph, taken in Udupi, India, in May 2021, shows the seven brightest stars in the constellation Ursa Major. This asterism was seen as a Wagon by the Babylonians, which probably led to the alternative interpretation of the Chariot in the didactic poem of the Greek poet Aratus. The normal Greek interpretation is the constellation of the Great She-Bear, which also includes many fainter stars in a much broader area of the sky. In ancient Egypt, these seven stars form the figure of the Bull’s Foreleg or the Bull’s Thigh. It is considered a part of the leg of the god Seth, who was considered the evil one of two brothers; the god Osiris (who is sometimes considered the first king of Egypt) was murdered by his brother Seth. Their loving sister put together the scattered pieces of the corpse and reanimated him. In order to prevent Seth from further evil deeds, this leg was attached to a dowel in the sky. These seven bright stars were considered The Northern Dipper, containing the asterism of the Judges by the nobility in Ancient China. In French and in Dutch, it is called a Saucepan, in German a Chariot and in British English a Plough. The commonly known term “Big Dipper” is American English. They are considered the male figure who is the father of all stars and humans in the North American Navajo saga, where he is said to be the husband of a mother goddess seen in Cassiopeia. Similarly, it is designated the Man’s Cart in Norse mythology with the Woman’s Cart in Ursa Minor. In some other northern cultures, the group is interpreted as an Elk, for instance for the Inuits and Siberians, while the Sami see the Bow and Arrow of Favdna here. In contrast, not all cultures in the southern hemisphere named it because it is always either close to the horizon or invisible. For instance, the Brazilian Tucano people called it the Large Anus of the Snake and in Samoa it forms part of the Heirloom Warclub. The Hawaiian people also used the asterism for navigation and called it The Seven, while the Macedonian tradition interpreted it as Seven Thieves. In Italian star lore, it is either called The Seven Oxen (Rome) or The Seven Brothers (Sardinia). Similarly, the Mongolian traditions speak of Seven Buddahs while the Indians call it the Seven Sages.
Credit: Arya Anthony/IAU OAE

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A person stands by a tree in a wintry landscape. Above, the sky is dominated by a large triangle of three bright stars.

Forgoing the Summer Triangle as it sets in the early winter evening

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   This image was taken from Nagano, Japan, in December 2018, and shows three prominent constellations: Aquila (towards the lower-left of the image), Cygnus (in the upper part of the image) and Lyra (bottom-right). The brightest stars within these constellations (Altair, Deneb and Vega) form the three vertices of the asterism known as the Summer Triangle. The star Altair is the brightest star towards the bottom-left of the image, Deneb is the brightest star towards the top-right of the image, and Vega is the brightest star towards the bottom-right of the image. In Asian cultures the stars Vega and Altair represent a love story between the weaver girl and the herdsman, who are separated by the faint band of the Milky Way, but in July are allowed to cross the heavenly river (the Milky Way) to be together. The Boorong people of Northeast Victoria, Australia, associate the reappearance of Vega — after its yearly disappearance from view — with the time when the Mallee fowls build nests. The Boorong also associate their indigenous constellation Neilloan with the goddess Mallee-hen (Vega), mother of Totyarguil (Altair), the hero who created the Murray River. In Wardaman traditions, the star Vega acts as a gateway to the Milky Way for spirits of the deceased. The star name Altair is abbreviated from the Arabic “Al-Nasr Al-Ta’ir” (meaning “The Flying Eagle”) proving that the constellation of the Eagle (Aquila) is one of the most stable ones in history. Originating from the Babylonian epoch (carrying a king towards the sky), it was taken over by the Greeks, Romans, and Arabs. The star name Deneb comes from the Arabic word “dhanab”, meaning “tail”, and refers to the Greek constellation of The Bird that is interpreted in the Roman tradition as a Swan (Cygnus), and as a Hen in the Arabic world. The third star name, Vega, comes from the Arabic “Al-Nasr Al-Waqi”, meaning “The Swooping Eagle'', because the indigenous (pre-Islamic) Arabic culture had a second eagle in the area of the Greek constellation Lyra. In the Early Modern Age, some Christian astronomers, inspired by the Arabic tradition, depicted this constellation as an eagle or vulture holding a lyre. The image also shows a range of other constellations, including Delphinus, Sagitta, and Vulpecula. According to Greek mythology, Sagitta, The Arrow, carried the god of light and the goddess of fertility. In winter they set in the evening but in spring they rise again in the east, and are present for longer and longer in order to make the land fruitful and agriculture successful.
Credit: Kouij Ohnishi/IAU OAO

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Five bright stars form the shape of the letter M.

Portrait of a Bat

Caption: Honourable mention in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   Taken in November 2019 from the Doi Inthanon National Park, Chiang Mai, Thailand, this image captures the notable northern constellation Cassiopeia, in the shape of the letter M. Although the official constellation name is the Latinised version of the name of queen “Kasseipeia” from Greek mythology, these five bright stars were considered a constellation in many cultures around the world and they are associated with diverse stories. In Thailand, for example, the constellation represents a Bat, while in Hawaiian culture it is called 'Iwa Keli'i, the chief frigate bird. For the Navajo in North America, the bright stars are the central part of the celestial mother (of all stars and humans) revolving around the celestial pole together with her husband, the celestial father (of all stars and humans) seen in the constellation of Ursa Major. For the Maya it was part of the huge constellation of the Hole-Backed Caiman, and for the Inuit a Lamp Stand and a Blubber Container. In ancient China, the bottom-left star was associated with the mythological general Wangliang who drove four horses, represented by the two bright and two fainter stars of the M’s next stroke (from upper-left to lower-middle). The remaining two bright stars and a couple of the other fainter ones are considered a Flying Corridor, a sort of highway, next to the Emperor’s Forbidden Palace that is located at the northern polar region. On the island of Tonga in the South Pacific, this asterism is considered the Wing of Tafahi and it is not clear if this refers to the shape of the island of Tafahi, or if it is based on an error and originally referred to a wing of the Polynesian hero Tafaki. The various colours of the stars indicate their temperatures, with redder stars being relatively cooler on their surface than blue and white stars.
Credit: Thanakrit Santikunaporn/IAU OAE

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The bright Moon illuminates a beach. Three bright planets form a line below and to the right of the Moon.

To guard the Stars and the Sea Together

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns. This image composition is amazing. In the far background of the landscape we see a chain of mountains that seems to mirror the structure of the Milky Way in the sky above. The strong daylight-like colours of the landscape are caused by the Moon, the bright light at the top of the image. Taken in Kinabalu, Malaysia, in February 2019, this image shows the alignment of planets and the Moon, conveying the idea of the ecliptic as the central line of the Zodiac, the plane within which all planets orbit the Sun. The ecliptic is the central line of the Zodiac, so the region of about five to 10 degrees either side of the ecliptic is where the constellations of the Zodiac are located. Starting from the horizon towards the bottom left of the image we can see the planets Venus, Saturn and Jupiter. The planets have different cultural significance for people around the world, and are deeply embedded in social, religious and practical aspects of life. For example, Wardaman traditions of Indigenous Australians associate the planets with ancestor spirits who traverse the Celestial Road (ecliptic). The appearance and disappearance of planets in the sky are associated with various ceremonies. For example, when Venus starts being the “Morning star” after having been the “Evening star”, this marks the Banumbirr ceremony for the Yolnu people of Arnhem Land, in Australia. The image also shows the constellations Scorpius, Aquila, Lupus and Triangulum Australe, the asterism of the Teapot, and the two pointer stars Alpha and Beta Centauri. The constellations, asterisms and individual stars within them have significance in many different cultures. Malaysia, being close to the equator, has had connections to the north as well as to the south and almost the whole sky is visible over the course of the year. The star Antares is seen by the Kokatha people of the Western Desert as Kogolongo, the red tailed black cockatoo, while the Boorong refer to it as Djuit, the red-rumped parrot. The two stars which form the stinger of Scorpius (Shaula and Lesath), are called Karik Karik, the Australian Kestrel.
Credit: Likai Lin/IAU OAE

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The diffuse glow of the Milky Way broken by dark patches. Right, the red star Antares forms the top of a hook-like pattern

Milky Way Arch over La Palma

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   This image, which shows the majestic band of the Milky Way and a range of culturally significant patterns, was taken in May 2022 at a very high altitude from the Roque de los Muchachos Observatory in La Palma, from which one can see the clouds below. Some prominent star patterns include Scorpius, Sagittarius, Lyra, Cygnus, Aquila, the Summer Triangle asterism, and the Teapot asterism. As the Canary Islands used to be a starting point for European sailors to explore the world, we use this place to point to the many indigenous cultures they encountered. Most notably it is the dark patterns within the band of the Milky Way that hold significance for many Indigenous cultures around the world. The dark patterns are in fact dense, cool clouds of gas and dust that block the light from stars. Indigenous people see caves, waterways and various patterns associated with the dark regions of the Milky Way. The constellations and patterns hold different cultural significance and interpretations for different people. For example, the constellation Scorpius is referred to by Polynesian people as the demigod Maui’s Fishhook. The Yolnu people of Arnhem Land associate Scorpius with a crocodile called Ingalpir. Some Indigenous Australian groups associate stories with individual stars within Scorpius, most notably Antares, the orange-red star in the top right of the image above the band of the Milky Way. Next to the Scorpion and above the bright centre of the Milky Way, there is a prominent dark cloud that is called the Pipe Nebula by modern astrophotographers. The smoke of this pipe goes up to rho Ophiuchi. This and all the other dark clouds in the Milky Way together form the backbone of heaven for some tribes, and an animal with black-and-white skin for South African Zulu people. The nomenclature of bright stars also has cross-cultural roots. For example, Vega (the bright blue star towards the top of the image) comes from the Arabic waqi, from al-nasr al-waqi, the Eagle who throws himself down (in order to hunt). This contrasts with the Flying Eagle, Altair, also derived from Arabic. Antares is a Greek word meaning “the one similar to Mars”, referring to its colour. The star name Shaula in the stinger of the Scorpion is a modern version of the Babylonian or even Sumerian star name.
Credit: Amirreza Kamkar/IAU OAE

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The ladle-shaped Big Dipper with the orange star Arcturus to its left. Right is the diffuse disk-shaped Andromeda galaxy

Dreamlike Starry Sky and Airglow

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   This spectacular image shows a range of prominent constellations visible in the night sky over the desert of inner Mongolia, taken in August 2019. The yellowish star in the bottom left side is Arcturus, one of the brightest stars in the night sky, and the brightest in the constellation Boötes. The handle of the Big Dipper points towards this bright star and the Dipper is also visible above Boötes. The Northern Dipper (Bei Dou) is a traditional Chinese constellation. It is considered a chariot in which the Judges for Nobility are sitting. Arcturus is considered a single-star asterism, named the Horn, which forms part of the Chinese super-constellation for the spring, the Azure Dragon of the East. The front of the Northern Dipper points towards the star at the top of the photograph which is now called Polaris, the northern Pole Star. In ancient China, there was no bright star at the pole, so the stars in the nearest vicinity of the pole were considered to belong to the emperor and his family in the constellation the Purple Forbidden Palace. At least as early as mediaeval times, Polaris was considered part of the constellation of the Great Emperor of Heaven. Corona Borealis is also visible in the top right corner of this image, although not in its completeness. It is called the Coiled Thong in China. With its characteristic semi-circular shape, this is one of the smaller constellations of the 88 modern ones, but also can be traced back at least three or four millennia through the Roman “Crown”, the Greek wedding “Wreath”, and the Babylonian “Asterism of Dignity”. The modern name literally means “Northern Crown” in Latin. At the upper-right edge of the image, we find the part of the modern constellation Cassiopeia that is considered the Flying Corridor and an Auxiliary Road in ancient China. The W-shape of Cassiopeia is cut off by the edge of the photograph but the constellations to its south and southeast, Andromeda and Perseus, are clearly recognisable. Prominently we see the Andromeda galaxy, the most distant object that is visible to the unaided eye. It is located at the outermost outliers of the band of the Milky Way, which could explain why it has not been mentioned explicitly in ancient star catalogues, as it was mistakenly thought to be part of the Milky Way. The photograph also shows clearly reddish parts of the Milky Way that don’t appear bright to the naked eye, and also open clusters that are formed from the same molecular cloud, i.e., groups of stars with similar ages. This region is part of many big and small asterisms in traditional Chinese uranology.
Credit: Likai Lin/IAU OAE

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Orion appears as an hourglass shape of stars in the bottom of the image. Above Taurus is v-shaped with a small star cluster

Romanian Orion

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   Taken in Romania in August 2012, this image shows two of the most recognisable constellations in the sky, Orion and Taurus. Orion, the Hunter, is found near the horizon. The most prominent star visible in this image is Betelgeuse, while the asterism of Orion’s belt is formed by three aligned bright stars. Just above Orion we can find Taurus, one of the constellations of the Zodiac. As the Zodiac is inherited from Babylon, The Bull of Heaven represents a mighty but dangerous creature that was defeated by King Gilgamesh and his friend Enkidu. They cut the Bull in half and sacrificed the animal to the gods in order to protect their people. Taurus is also home to the star cluster Pleiades, also known as the Seven Sisters. Two planets are visible: Venus, the bright spot near the fence, and Jupiter, the bright spot at the top, next to the Bull’s face. Different cultures have included the stars of these constellations in their own mythology. The Romanians, for instance, after Christianisation identified four other constellations using some of the stars of Orion and others surrounding it. One such constellation is called Trisfetitele (the Three Saints), which is associated with the three stars comprising Orion's Belt, representing the Three Hierarchs Basil, Gregory and John. This same asterism is also called Three Wise Men, Kings from the East or just Three Kings — all of these names being rooted in the Christian religion. The agricultural calendar, in contrast, led farmers to define two other constellations, the Little Plough and the Sickle. Both are seen in the southern half of the Orion rectangle; the Little Plough is drawn by connecting the southern quadrilateral with Orion’s left shoulder, and the Sickle is formed by connecting Orion’s left foot (Rigel) with the belt stars, forming an arch and completing the form of a hoe. In the cultural calendar, these constellations were used to announce the harvest of wheat/grain. Finally, the fourth Romanian constellation is the Great Auger, where Orion’s belt represents the handle of the auger, and Betelgeuse is the tip, facing towards Pollux in Gemini. This constellation is associated with treasure, as Romanian peasants believe that the Auger points to the treasure when they approach the end of the world. Most of the official star names in Orion are Arabic; Mintaka (meaning “belt”) is at the waist; Alnitak (meaning “girdle”) and Alnilam (meaning “string”) are at the belt; and Rigel (meaning foot) is at the left foot. The star on the left shoulder is named Bellatrix, the Latin term for a female warrior. The star at the right leg is called Saiph, for the sword or sabre of the Arabic Orion.
Credit: Alex Conu/IAU OAE

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The Big Dipper, seven bright stars shaped like a ladle, viewed in 4 seasons, each time at a different angle

Big Dipper in Four Seasons

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   As Earth moves around the Sun, the positions of the stars in the night sky appear to change over the course of the year. This is well exemplified in this mosaic, with images taken in all four seasons throughout 2020 in the region of Veneto, Italy, showing the apparent motion of the Ursa Minor and Ursa Major constellations. Ursa Minor, the Little Bear, is a constellation of the northern hemisphere, and it contains the northern celestial pole, in our current epoch marked by a bright star called Polaris or the Pole Star. For centuries Polaris has been used for navigation in the northern hemisphere, as it has been almost at the exact pole position for roughly 200 years. In the Middle Ages and antiquity, there was no pole star; the celestial north pole lay in a dark region and the Greeks considered the “Little She-Bear” as a companion of the “Great She-Bear”, which is more easily recognizable. The brightest stars of these constellations were alternatively also considered as chariots by the Greeks, as written in Aratus’s famous didactic poem from the 3rd century before the common era. The most famous asterism in Ursa Major, composed of seven stars, has different names across the (northern) world. While considered as a chariot by the Greeks, it is “The Northern Dipper” in China, and “The Seven Oxen” for the ancient Romans. It was also the navigational purpose that led to the name The Great She-Bear, Ursa Major; for the Greeks, travelling towards the direction of the horizon above which Ursa Major appears meant moving towards the land of the bears (northern Europe). An animal is clearly recognizable when taking into account all the fainter stars in the vicinity of the seven bright ones. They considered it a female bear because Greek mythology connects this animal with the nymph Callisto, whose story describes the initiation rituals for women. In the top left, we see an image taken on a spring evening, while the image below shows the same portion of the sky on a summer evening. Going counterclockwise, we see the sky during autumn in the bottom right image, while the top right finally shows this portion of the sky in the winter. Note that the relative positions of Ursa Minor and the Big Dipper don’t change, but all stars appear to be moved in a circle around Polaris. This star pointing due north lies at the point where Earth’s rotational axis intersects the celestial sphere. The shift of constellations throughout the year is therefore a globe-clock or a globe-calendar, used by ancient civilizations to measure the year, and to predict the changes of seasons. It helps to establish, for instance, the best time for sowing and sailing as winds change with the seasons.
Credit: Giorgia Hofer/IAU OAE

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