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Come to know the Summer Triangle

A chart showing Vega, Deneb and Altair connected by thin purple lines.
The bright stars Vega, Deneb and Altair make up the easy-to-spot Summer Triangle.

Vega, Deneb and Altair

The Summer Triangle is an asterism, not a constellation. It’s made of three bright stars in three different constellations. These stars are Vega, Deneb and Altair. We in the Northern Hemisphere can see the Summer Triangle for part of the night, at any time of the year. But seeing it in summer is the most fun! It’s most prominent in the northern summer season. So, as dusk deepens into night on a warm June or July night, look eastward for this great star pattern.

It’s difficult to convey the huge size of the Summer Triangle. At nightfall in northern summer, look for the most brilliant star in your eastern sky. That’ll be Vega, the brightest star in the constellation Lyra the Harp.

Look to the lower left of Vega for another bright star. It’s Deneb, the brightest in the constellation Cygnus the Swan and the third-brightest star in the Summer Triangle. An outstretched hand at arm’s length approximates the distance from Vega to Deneb.

Look to the lower right of Vega to locate the Summer Triangle’s second-brightest star. It’s Altair, the brightest star in the constellation Aquila the Eagle. A ruler held at arm’s length (12 inches or 30 cm) fills the gap between these two stars.

Photo of sky with stars, Summer Triangle stars and their constellations, all labeled.
The Summer Triangle, as captured and composed by our friend Susan Gies Jensen in Odessa, Washington.

Summer Triangle as a road map to the Milky Way

If you’re lucky enough to be under a dark sky on a moonless night, you’ll see the great swath of stars known as the Milky Way passing between the Summer Triangle stars Vega and Altair. The star Deneb bobs in the middle of this river of stars that passes through the Summer Triangle, and arcs across the sky. Although every star that you see with the unaided eye is actually a member of our Milky Way galaxy, often the term Milky Way refers to the cross-sectional view of the galactic disk, whereby innumerable far-off suns congregate into a cloudy trail of stars.

Once you master the Summer Triangle, you can always locate the Milky Way on a clear, dark night. How about making the most of a dark summer night to explore this band of stars, this starlit boulevard abounding with celestial delights? Use binoculars to reel in the gossamer beauty of it all, the haunting nebulae and star clusters of a midsummer night’s dream!

Some see the Summer Triangle as a great big “V” for vacation, with Altair marking the point of the “V.” In summer, the Summer Triangle appears in the east at nightfall, high overhead after midnight and in the west at dawn. All night long on a summer night, the stars of the Summer Triangle – as if school kids on vacation – waltz amidst the streetlights of the Milky Way galaxy.

2 long, dim, fuzzy white bands across photo, with dark band between them and with Summer Triangle marked.
View larger. | Great Rift of Milky Way passes through the constellation Cassiopeia and the Summer Triangle.

Summer Triangle as nature’s seasonal calendar

The Summer Triangle serves as a stellar calendar, marking the seasons. When the stars of the Summer Triangle light up the eastern twilight dusk in middle to late June, it’s a sure sign of the change of seasons, of spring giving way to summer. However, when the Summer Triangle is seen high in the south to overhead at dusk and early evening, the Summer Triangle’s change of position indicates that summer has ebbed into fall.

Bottom line: How to find the Summer Triangle – an asterism, or noticeable pattern of stars – consisting of the three bright stars Vega, Deneb and Altair.

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June 4, 2021
Sky Archive

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Bruce McClure

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