Which of the following stars is NOT part of the Summer Triangle?

Sirius is not part of the Summer Triangle, which is an asterism formed by three bright stars: Vega, Deneb, and Altair. The Summer Triangle is prominent in the night sky during the warmer months, and each of these stars is located in different constellations—Vega is in Lyra, Deneb is in Cygnus, and Altair is in Aquila.

On the other hand, Sirius, known as the brightest star in the night sky, is actually part of the constellation Canis Major. It is prominent in the winter sky rather than the summer, further distinguishing it from the stars that compose the Summer Triangle. Understanding the relationships between these stars and their respective constellations is key to identifying their locations and significance in astronomy.