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The Constellations of the Summer Triangle

written by: George Garza•edited by: RC Davison•updated: 5/19/2011

Stars from three constellations in the northern hemisphere form an imaginary triangle - the Summer Triangle, which is an asterism. The constellations Aquila, Cygnus, and Lyra contain the stars Altair, Deneb, and Vega. Together these stars create a nightly picture of a triangle in space.

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    The Summer Triangle

    As you would expect, given its name, the Summer Triangle predominates the sky during the summer season. However, the constellations of the summer triangle can be seen for at least a portion of the night at any time during the year (in mid-northern latitudes). This asterism is a large triangle formed by the three first-magnitude stars Altair, Deneb, and Vega. It is best seen during northern summer and autumn evenings.

    Summer Triangle 

    To get a feel for the constellations see a List of Constellations Names

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    Altair in The Constellation Aquila

    Altair is the brightest star located in the constellation Aquila and it forms one vertex of the Summer Triangle. It has a magnitude 0.76 making it the the twelfth-brightest star in the sky. It is a spectral class A7 dwarf star and it is 16.8 light years away. (The spectral classification in astronomy, is a classification of the stars by their temperature and spectrum.)


    Other facts about Altair:

    • Astronomical Name: Alpha Aquilae.
    • Meaning: From Arabic: "The Eagle".
    • Apparent Magnitude: 0.76.
    • Absolute Magnitude: 2.20.
    • Distance (light-years): 16.8.

    Altair is easily recognized, because it is situated on either side along a straight line by two stars, Alshain and Tarazed (Beta and Gamma Aquilae). It is also one of the nearest bright stars and it has an exceptional rotation rate. Using Doppler shift measurements, it rotates more than three times on its axis in one of our days, as compared to one rotation in 25 days for our Sun.

    Other points of interest. There are nine main objects in the constellation:

    • Altair, the Flying One (one of the stars in the Summer Triangle)
    • Alshain, the Falcon
    • Tarazed, the Plundering Falcon
    • Deneb El Okab "Tail of the Falcon"
    • Deneb Zeta
    • Bezek "lightning"
    • Tseen Foo "The heavenly raft"
    • Al Thalmain The two ostriches
    • Eta
    • Iota

    See Also: Nothing but the Facts About Constellation Aquila

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    Deneb in the Constellation Cygnus

    In the months between June and October, Cygnus, the Swan, can be seen in the northern hemisphere. The stars form a distinctive large cross, and the constellation is also known as the Northern Cross. Cygnus is also the home of Cygnus X-1, a well known black hole candidate. Finally, the constellation also contains two Messier objects, both of which are open star clusters.

    Here are some interesting facts about Deneb:

    • It is a white supergiant (A2 1a Spectral Class)
    • Distance: (light years) 1800.
    • Diameter: it is very large, 60 times the Sun's diameter
    • Mass: 30 times the Sun's mass.
    • Luminosity: It is also 60,000 more luminous that the Sun.


    Some of the other stars in the Cygnus constellation are:

    • M39 an Open Star Cluster
    • M29 an Open Star Cluster
    • Deneb "Tail of the Hen" (Summer Triangle Star)
    • Albireo also known as "Beak of the Hen"
    • Sadr which means "Breast"
    • Gienah Cygni which means "Wing"
    • Azelfafage

    If Cygnus interests you, consider the article Nothing but the Facts About the Constellation Cygnus

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    Vega in the Constellation Lyra

    A small but an easy to spot constellation in the northern skies, Lyra contains the star Vega (the fifth brightest star in the night sky). It is an ancient constellation, listed by Ptolemy in the 2nd century. Lyra represents the lyre or harp of the Greek musician Orpheus. As legend has it, Orpheus played the instrument so well he could tame wild beasts with its music, and even impressed the gods with his abilities. Lyra can be found high in the night sky, underneath another star constellation, the head of Draco, the dragon. Lyra is visible throughout the summer and well into the fall and is the last of the three constellations that make up the Summer Triangle.

    The Constellation Lyra 

    Here are some facts about Vega:

    • It is a blue-white star (spectral class A0 V)
    • Astronomical Name: Alpha Lyrae
    • Meaning: from the Arabic: vulture or eagle
    • Apparent Magnitude: 0.03
    • Absolute Magnitude: 0.58
    • Distance in light-years: 25
    • Luminosity: 37 times a bright as the Sun

    Stars and other objects in Lyra: There are seven object in the constellation.

    • M56 Globular Cluster
    • M57 Planetary Nebula
    • Vega the Falling Eagle (Summer Triangle Star)
    • Sheliak
    • Sulafat
    • Aladfar
    • Althafar

    If you want more information about Vega see: Vega Star Facts

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    So what is the Summer Triangle? It is a group of stars made from 3 different constellations. This is called an asterism, an astronomical pattern formed by stars that are not in the same constellation or are part of an official constellation. The stars are Altair, Deneb and Vega. They belong to the constellations Aquila, Cygnus, and Lyra. They are located in the northern hemisphere, and they are basically summer constellations.

    Learn about asterisms at Explore Astronomical Asterisms

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    The Constellations of the Summer Triangle

    Image: JPL/Nasa

    The Constellation Aquila


    The Constellation Cygnus


    The Constellation Lyra


    Stargazing is important in finding constellations see:The Basics Of Stargazing