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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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Related Diagrams


Sagittarius is shaped like a teapot pouring tea south west. The ecliptic runs WSW to ENE at the top of the constellation

Sagittarius Constellation Map

Caption: The constellation Sagittarius along with its bright stars and surrounding constellations. Sagittarius is surrounded by (going clockwise from the top) Aquila, Scutum, Serpens Cauda, Ophiuchus, Scorpius, Corona Australis, Telescopium, Microscopium and Capricornus. The brighter stars in Sagittarius form a distinctive teapot shape. Sagittarius lies on the ecliptic (shown here as a blue line), this is the path the Sun appears to take across the sky over the course of a year. The Sun is in Sagittarius from mid December to mid January. The other planets of the Solar System can often be found in Sagittarius. Sagittarius lies south of the celestial equator. The famous teapot asterism is visible for all but the most arctic regions of the world but the most southerly parts of the constellation are not visible in northern parts of Asia, Europe and North America. Sagittarius is most visible in the evenings in the northern hemisphere summer and southern hemisphere winter. The supermassive black hole Sagittarius A* which lies at the center of our Milky Way Galaxy is sits on the western (here right-hand) edge of Sagittarius. Due to it covering an area at the center of our Galaxy, Sagittarius is home to many star clusters including open clusters (marked here with yellow circles) and globular clusters (marked here with yellow circles with + signs superimposed on them). Three nebulae are also marked here with green squares. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries, nor the line marking the ecliptic, nor the lines joining the stars appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons


Ursa Major appears as a ladle with the handle to the east & the cup to the west. Lines of fainter stars extend to the south

Ursa Major Constellation Map

Caption: The constellation Ursa Major along with its bright stars and its surrounding constellations. Ursa Major is surrounded by (going clockwise from the top): Draco, Camelopardalis, Lynx, Leo Minor, Leo, Coma Berenices, Canes Venatici and Boötes. Ursa Major is famous for the prominent asterism often known in English as the Big Dipper or the Plough. This prominent northern asterism has a wide variety of names from cultures across the world. While most constellations and asterisms are made up of unrelated stars that randomly appear close together on the sky, five of the stars in the Big Dipper are part of the Ursa Major Moving Group, a group of stars moving through space together that likely formed in the same location 300 million years ago. The two stars on the right-hand end of the Big Dipper on this diagram form a pair of pointer stars that can be used to locate Polaris, the northern pole star which lies in the constellation of Ursa Minor. Ursa Major is a northern constellation and is visible from northern and equatorial regions. Parts of the constellation are visible from all but the most antarctic parts of the southern hemisphere but not all temperate regions of the southern hemisphere can see all of the Big Dipper. Conversely the Big Dipper and much of the rest of the constellation are circumpolar in arctic and many temperate regions of the northern hemisphere. Ursa Major is most visible in the evening in the northern hemisphere spring and southern hemisphere autumn. Two prominent galaxies appear in the northern part of this constellation, the spiral galaxy M81 and M82, a possible spiral galaxy whose structure is difficult to observe from the Earth as it appears edge-on. Both are shown here as red ellipses. The planetary nebula M97 (the Owl Nebula) lies in the middle of the constellation and is marked by a green circle superimposed on a plus symbol. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries, nor the lines joining the stars appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons


Aquila looks like a simplified arrow shape with the head pointing to the lower right (the south west). Altair is in the tail

Aquila Constellation Map

Caption: The constellation Aquila with its bright stars and surrounding constellations. Aquila is surrounded by (going clockwise from the top): Sagitta, Hercules, Ophiuchus, Serpens Cauda, Scutum, Sagittarius, Capricornus, Aquarius and Delphinus. Aquila is most notable for its brightest star Altair. This forms one vertex of the prominent Summer Triangle asterism that is visible in northern hemisphere summer evenings. Aquila spans the celestial equator and thus some part of it is visible from all of the Earth at some point in the year. It is most visible in the evenings in the late northern hemisphere summer and late southern hemisphere winter. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. The blue line in the lower right of the diagram is the ecliptic. Neither the constellation boundaries, nor the line marking the ecliptic, nor the lines joining the stars appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons


Cygnus looks like a swan in flight with the neck pointing to the lower right (south-west). Deneb is the tail

Cygnus Constellation Map

Caption: The constellation Cygnus with its bright stars and surrounding constellations. Cygnus is surrounded by (going clockwise from the top): Cepheus, Draco, Lyra, Vulpecula, Pegasus and Lacerta. Cygnus is notable for its brightest star Deneb. This forms one vertex of the prominent Summer Triangle asterism that is visible in northern hemisphere summer evenings. Cygnus is a northern constellation and thus the whole of the constellation is visible at some point in the year in the whole northern hemisphere. The whole constellation is also visible from equatorial regions of the southern hemisphere with parts of the constellation visible from temperate southern regions. The plane of the Milky Way runs through Cygnus and thus the constellation is rich in nebulae and star clusters. These include the North America Nebula (NGC 7000) and the Crescent Nebula (NGC 6888). The Veil Nebula is a huge supernova remnant, parts of which are marked here as NGC 6960 and NGC 6992/5. All of the previously-mentioned nebulae are marked with green squares. The planetary nebula NGC 6826 is marked here with a green circle superimposed on a plus sign. The open star clusters M29 and M39 are marked here with yellow circles. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries, nor the lines joining the stars appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons


Pegasus appears as a square with lines extending west from its western two vertices

Pegasus Constellation Map

Caption: The constellation Pegasus with its bright stars and surrounding constellations. Pegasus is surrounded by (going clockwise from the top): Lacerta, Cygnus, Vulpecula, Delphinus, Equuleus, Aquarius, Pisces and Andromeda. Pegasus is known for the prominent asterism the “Square of Pegasus” which consists of its three brightest stars plus the brightest star in Andromeda. Pegasus is a northern constellation and thus the whole constellation is visible at some point in the year throughout the northern hemisphere. The whole constellation is also visible to southern hemisphere equatorial and temperate zones with parts of the constellation visible from all but the most antarctic regions. Pegasus is best viewed in the evening in the northern hemisphere autumn and southern hemisphere spring. The globular cluster M15 lies in Pegasus and is marked here with a yellow circle with a plus sign superimposed on it. The spiral galaxy NGC 7331 also lies in Pegasus and is marked here with a red ellipse. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. The blue line at the bottom of the diagram marks the ecliptic. Neither the constellation boundaries, nor the lines joining the stars, nor the ecliptic, appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons