Orion's Belt or The Belt of Orion is an asterism within the constellation. The Summer Triangle is an astronomical asterism in the northern celestial hemisphere. Star sapphires and rubies get their asterism from rutile impurities present. Some rose quartz contains microscopic rutile needles which produces an asterism in transmitted light. The "Drinking Gourd" is another name for the Big Dipper asterism. Within the 'W' asterism formed by Cassiopeia's five major stars lies Cassiopeia A (Cas A). Small rutile needles present in gems are responsible for an optical phenomenon known as asterism. Its brightest star, Altair, is one vertex of the Summer Triangle asterism. Orion's seven brightest stars form a distinctive hourglass-shaped asterism, or pattern, in the night sky. The asterism "Big Dipper" may be used to find Polaris. Delphinus' brightest stars form a distinctive asterism that can easily be recognized. Additionally, Rigel is part of the Winter Circle asterism. The name was also derived from the city's establishment on the auspicious asterism called Anura. This group is south of the prominent asterism, Orion's Belt. The most prominent feature of Crux is the distinctive asterism known as the Southern Cross.