The Summer Triangle is called that because its three bright stars dominate the high night sky during the summer months in the Northern Hemisphere.
It is an asterism, which is an easy-to-recognize pattern of stars rather than an official constellation.
It is formed by connecting three extremely bright stars from three separate constellations:
Vega in the constellation Lyra (the Harp)
Deneb in the constellation Cygnus (the Swan)
Altair in the constellation Aquila (the Eagle)
High overhead: During summer evenings in the Northern Hemisphere, these three bright stars rise high into the middle of the night sky, making them hard to miss.
Historical term: While stargazers in various ancient cultures noticed the grouping, the specific name "Summer Triangle" was used in the West by the early 20th century and popularized by British astronomer Patrick Moore in the mid-20th century.
Seasonal visibility: Although you can actually see the triangle during other seasons (like spring mornings or autumn nights), it is most prominent and convenient to view during warm summer nights.
Look toward the eastern sky after sunset during late June and July, or high overhead during late summer evenings. Scan for the three brightest stars that form a large, wide triangle shape spanning the sky. Use the triangle as a guide to locate the Milky Way, which runs directly through the middle of the three stars under clear, dark skies. image Credit Sberardi
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