As suggested by its name, the Summer Triangle predominates during the summer season. Even so, the Summer Triangle can be seen for at least part of the night at any time of the year (from mid-northern latitudes).
As dusk deepens into night on a warm June or July night, look eastward for a sparkling blue-white star, whose name is Vega. Reigning at the apex of the celebrated Summer Triangle, Vega overwhelms as the brightest of the Summer Triangle’s three glorious stars, all bright enough to be seen from many light-polluted cities.
It’s difficult to convey the huge size of the Summer Triangle asterism – a star pattern that is NOT a constellation. At nightfall in summer, look for the brightest star in your eastern sky. That’s Vega, the brightest star in the constellation Lyra the Harp. Look to the lower left of Vega for another bright star – Deneb, the brightest in the constellation Cygnus the Swan and the third brightest in the Summer Triangle. An outstretched hand at an arm length approximates the distance from Vega to Deneb.
Look to the lower right of Vega to locate the Summer Triangle’s second brightest star. That’s Altair, the brightest star in the constellation Aquila the Eagle. A ruler held at an arm length fills the gap between these two stars.
Road map to the Milky Way
If you’re lucky enough to be under a dark starry sky on a moonless night, you’ll see the great swath of stars known as the Milky Way passing in 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, oftentimes 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.
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.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.