As Earth revolves around the sun, the night side of the planet points in different directions in space. We are now positioned to see the stars of winter. However, because of the long hours of darkness now, some of the prominent summer star patterns remain visible for a short time after sunset. One of those groupings is the three constellations that make up the Summer Triangle.
The triangle is formed by linking Vega, the brightest star in Lyra, the Harp, with Altir, the brightest star in Aquila, the Eagle. Vega sits just above the northwestern horizon while Altir sits above the western horizon. The third constellation in the triangle is Cygnus, the Swan, and its brightest star, Deneb. Within the classic outline of the swan there is a smaller pattern of stars that form a cross. It's been named the Northern Cross, and at Christmastime each year it stands upright on the northwestern horizon.
Be sure to take some time this holiday season to search for the Summer Triangle.science