Asterism (astronomy)

asterismasterismsFalse Crossconstellationgroup of starsconstellations
In observational astronomy, an asterism is a popularly known pattern or group of stars that can be seen in the night sky.wikipedia
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Star

starsstellarmassive star
In observational astronomy, an asterism is a popularly known pattern or group of stars that can be seen in the night sky.
Historically, the most prominent stars were grouped into constellations and asterisms, the brightest of which gained proper names.

Ursa Major

Great BearOrsa MaggioreUrsa Major constellation
For example, the asterisms known as The Plough (Charles' Wain, the Big Dipper, etc.) comprises the seven brightest stars in the International Astronomical Union (IAU) recognised constellation Ursa Major.
Ursa Major is primarily known from the asterism of its main seven stars, which has been called the "Big Dipper," "the Wagon," "Charles's Wain," or "the Plough," among other names.

Crux

Southern CrossSouthern Cross constellationCrux Australis
Another is the asterism of the Southern Cross, whose recognised constellation is Crux.
Its name is Latin for cross, and it is dominated by a cross-shaped or kite-like asterism that is commonly known as the Southern Cross.

Constellation

constellationsEuropean constellationModern constellation
This colloquial definition makes it appear quite similar to a constellation, but they differ mostly in that a constellation is an officially recognized area of the sky, while an asterism is a visually obvious collection of stars and the lines used to mentally connect them; as such, asterisms do not have officially determined boundaries and are therefore a more general concept which may refer to any identified pattern of stars.
Other star patterns or groups called asterisms are not constellations per se, but are used by observers to navigate the night sky.

Arcturus

ArcturiansArcturianAlpha Boo
Together with Spica and Denebola (or Regulus, depending on the source), Arcturus is part of the Spring Triangle asterism and, by extension, also of the Great Diamond along with the star Cor Caroli.

Summer Triangle

Chinese constellationsthird star forms a symbolic bridge
The Summer Triangle is an astronomical asterism in the northern celestial hemisphere.

Deneb

Alpha CygniAridedα Cyg
Deneb is one of the vertices of the asterism known as the Summer Triangle and the "head" of the Northern Cross.

Cygnus (constellation)

CygnusCygnus constellationconstellation of Cygnus
Cygnus is one of the most recognizable constellations of the northern summer and autumn, and it features a prominent asterism known as the Northern Cross (in contrast to the Southern Cross).

Leo (constellation)

LeoLeoneLeo constellation
The lion's mane and shoulders also form an asterism known as "The Sickle," which to modern observers may resemble a backwards "question mark."

Orion (constellation)

OrionOrion constellationconstellation of Orion
This process was essentially arbitrary, and different cultures have identified different constellations, although a few of the more obvious patterns tend to appear in the constellations of multiple cultures, such as those of Orion and Scorpius.
Another name for the asterism of Alnilam, Alnitak and Mintaka is Väinämöisen vyö (Väinämöinen's Belt) and the stars "hanging" from the belt as Kalevanmiekka (Kaleva's sword).

Aquila (constellation)

AquilaAquilaeAql
Its brightest star, Altair, is one vertex of the Summer Triangle asterism.

Spica

α VirAzimechAlaezel
Spica, along with Arcturus and Denebola or Regulus depending on the source, is part of the Spring Triangle asterism, and by extension, also of the Great Diamond together with the star Cor Caroli.

Hyades (star cluster)

HyadesHyades clusterHyades star cluster
e.g. Both the open clusters The Pleiades or Seven Sisters and The Hyades in Taurus are sometimes considered asterisms, but this depends on the source.
Four of these stars, with Bayer designations Gamma, Delta 1, Epsilon, and Theta Tauri, form an asterism that is traditionally identified as the head of Taurus the Bull.

Altair

αAlpha Aquilaeα Aql
Altair is an A-type main sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the Summer Triangle asterism (the other two vertices are marked by Deneb and Vega).

Winter Hexagon

Winter Circle
The Winter Hexagon or Winter Circle/Oval is an asterism appearing to be in the form of a hexagon with vertices at Rigel, Aldebaran, Capella, Pollux, Procyon, and Sirius.

Pegasus (constellation)

PegasusPegasoPegasi
Alpha (Markab), Beta (Scheat), and Gamma (Algenib), together with Alpha Andromedae (Alpheratz, once also designated Delta Pegasi) form the large asterism known as the Square of Pegasus.

Gamma Pegasi

γ PegAlgenibγ
Gamma Pegasi (γ Pegasi, abbreviated Gamma Peg or γ Peg), formally named Algenib, is a star in the constellation of Pegasus, located at the southeast corner of the asterism known as the Great Square.

Vega

Alpha Lyrae2828Botercadent
This star lies at a vertex of a widely spaced asterism called the Summer Triangle, which consists of Vega plus the two first-magnitude stars Altair, in Aquila, and Deneb in Cygnus.

Alpha Pegasi

α PegMarkabα
Alpha Pegasi (α Pegasi, abbreviated Alpha Peg, α Peg), formally named Markab, is the third-brightest star in the constellation of Pegasus and one of the four stars in the asterism known as the Great Square of Pegasus.

Winter Triangle

The Winter Triangle is an astronomical asterism formed from three of the brightest stars in the winter sky.

Big Dipper

Northern DipperThe PloughPlough
For example, the asterisms known as The Plough (Charles' Wain, the Big Dipper, etc.) comprises the seven brightest stars in the International Astronomical Union (IAU) recognised constellation Ursa Major.
The Big Dipper (US, Canada) or the Plough (UK, Ireland) is a large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez, of third magnitude.

Beta Pegasi

Scheatβ Pegβ
It forms the upper right corner of the Great Square of Pegasus, a prominent rectangular asterism.

Northern Cross (asterism)

Northern Cross
The Northern Cross is a prominent astronomical asterism in the northern hemisphere celestial sphere, corresponding closely with the constellation Cygnus The Swan.

Johann Bayer

Bayer Johann BayerBayer, Johann
Two astronomers particularly known for greatly expanding the number of southern constellations were Johann Bayer (1572–1625) and Nicolas Louis de Lacaille (1713–1762).
Bayer is most famous for his star atlas Uranometria Omnium Asterismorum ("Uranometry of all the asterisms"), which was first published in 1603 in Augsburg and dedicated to two prominent local citizens.