The 72 inch (1.83 meter) Plaskett telescope at the Dominion Astrophysical Observatory, Victoria, British Columbia, Canada, in 1920. The instrument was the second largest telescope in the world and narrowly missed being the largest; it was completed and saw "first light" on May 6, 1918, only 6 months after the 100 inch Hooker telescope at Mount Wilson Observatory, California. The glass primary mirror is 73 inches in diameter and 12 inches (30 cm) thick, weighs 4340 lbs (1970 kg), and has a 10 1/8 inch hole in the center for the Cassegrain focus. The main tube is 31 feet (9.4 meters) long and weighs 12 tons. It is still in active use.