|During the summer months, the Summer Triangle star formation lights the sky from dusk until dawn. It consists of three bright stars: Vega in the constellation Lyra, Deneb in the constellation Cygnus, and Altair in the constellation Aquila.|
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-northen 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. Earthsky.org