The Summer Triangle is a prominent heavenly landmark associated with the summer sky. Formed from the brightest stars in the constellations of Aquila, Cygnus and Lyra, this huge isosceles triangle can be seen from mid-northern latitudes directly overhead during the summer months. From the southern latitudes, however, the asterism appears upside down and low in the hemisphere’s winter sky.
Winter vs. Summer Night Sky
Navigating around the winter night sky is relatively easy. That’s because the conspicuous constellation of Orion takes centre stage and is surrounded by at least another seven distinct constellations that are simple to spot. These include Taurus, Eridanus, Lepus, Canis Major, Canis Minor, Gemini and Auriga.
The summer night sky, on the other hand, is a little trickier to navigate. Once you have learned how to locate the Summer Triangle, however, you will then be able to find a number of nearby constellations. This include the three separate constellations which make up the asterism itself, namely Aquila, Cygnus and Lyra, as well as some other obvious constellations, such as Ursa Major and Scorpius.
You will also be able to spot some less obvious looking constellations in the summer sky, too. These will take a bit more time to master, though, including such constellations as Sagittarius, Draco, Hercules, Serpens, Ophiuchus, Lacerta, and Delphinus.
All White Main Sequence Stars
The Summer Triangle consists of the star Vega in Lyra (the Harp), Altair in Aquila (the Eagle), and Deneb in Cygnus (the Swan). During summer months in the Northern Hemisphere, these stars are often the first you see in the early evening eastern sky and by midnight appear virtually overhead. In the autumn, the Summer Triangle can also be seen to the west of the evening sky up until November when it subsequently disappears from view.
Vega in Lyra (the Harp) is located 25.3 light years from Earth and shines with a magnitude of 0.03. This also makes it the night sky’s 5th brightest star overall. Vega is a white main sequence star (A Class) that is blue-tinged. It is around 500 million years old, and has around double the Sun’s mass and radius, and 40 times its luminosity.
Altair in Aquila (the Eagle) is found 16.8 light-years away and has an apparent magnitude of 0.76, making it the 12th brightest star in the sky. Altair is a white A-type main sequence star. It is around 1.2 billion years old, and is almost double the Sun’s mass, 1.63 times its radius, and around 10 times its luminosity.
Deneb in Cygnus (the Swan) is situated 2,616 light years distant and has a magnitude of 1.25, making it the night sky’s 19th brightest star. Deneb is a blue-white A-type supergiant. It is around 10 million years old, with 19 times the Sun’s mass, 203 times its radius, and 196,000 times its luminosity.
Nearby Constellations of Summer Triangle
Once you have found The Summer Triangle, on a dark night you may be fortunate enough to view a misty cloud of stars running through it, which is actually the spiral arm of our own Milky Way galaxy. The Milky Way is difficult to view outside of rural areas free from light pollution, though, so spotting it is not always possible.
Finally, once you have managed to find The Summer Triangle, this celestial marker can then be used to quickly locate many other constellations in the summer skies. This include the nearby constellations of Hercules, Draco (the Dragon), Delphinus (the Dolphin), Sagitta (the Arrow), Vulpecula (the Fox), Ophiuchus (the Snake Holder), Serpens (the snake), Scorpius (the scorpion) and Sagittarius (the Archer).