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How big is 721.9 cubic kilometers?

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 It's about one-fifth as big as an Halley's Comet. In other words, 721.9 cubic kilometers is 0.18 times the size of an Halley's Comet, and the size of an Halley's Comet is 5.6 times that amount. (Comet Halley, officially "1P/Halley") (volume calculated based on 2005 dimensions) Halley's Comet, the famous comet visible to observers on Earth approximately every 76 years, has a peanut- or potato-shaped nucleus made of rock, dust, ice, and various frozen gasses. The nucleus measures approximately 15 km by 8 km by 8 km, which yields a calculated volume of 4,023 cu. km. The coma of the Comet — the trail of sublimated gasses that give the Comet its visibility — may be up to 100,000 km in length. It's about one-fifth as big as The Grand Canyon. In other words, 721.9 cubic kilometers is 0.173 times the size of The Grand Canyon, and the size of The Grand Canyon is 5.78 times that amount. (Coconino County and Mohave Counties, Arizona, near Fredonia and Grand Canyon, Arizona)A dynamic and continuously changing landscape, the Grand Canyon has an approximate volume of 4,170 cubic kilometers. The strata of the rock visible in the Canyon's walls display nearly 2 billion years of geological history. It's about 1,500 times as big as Sydney Harbour. In other words, 721.9 cubic kilometers is 1,280 times the size of Sydney Harbour, and the size of Sydney Harbour is 0.000781 times that amount. (formally Port Jackson, a.k.a. Sydney Harbor) (Sydney, New South Wales, Australia) (total estuary water volume at high tide)Lending the term "sydharb" or "sydarb" to comparable quantities of water, Sydney Harbor contains approximately 0.562 cubic kilometers of water. Snapper Island, a onetime naval facility loocated in the Harbour, was transformed by the dredging efforts of the Australian Navy from a 2,360 sq. m (25,400 sq. ft) outcropping to a 16,500 sq. m (178,000 sq. ft) island shaped roughly in the outline of a boat. It's about one-three-thousand-five-hundredth as big as The Gulf of Mexico. In other words, 721.9 cubic kilometers is 0.0002966 times the size of The Gulf of Mexico, and the size of The Gulf of Mexico is 3,372 times that amount. (water volume)The Gulf of Mexico contains 2,434,000 cubic kilometers of water. Every second, the Mississippi River empties 0.000012 cubic kilometers of water into the Gulf. It's about 300,000 times as big as The Great Pyramid of Giza. In other words, 721.9 cubic kilometers is 297,370.2 times the size of The Great Pyramid of Giza, and the size of The Great Pyramid of Giza is 0.000003362812 times that amount. (a.k.a. Pyramid of Khufu, a.k.a. Pyramid of Cheops) (Cairo, Egypt) (including internal hillock)The Great Pyramid of Giza has an estimated volume of 0.002427614 cubic kilometers including its internal hillock. The 2,300,000 stones used in the construction of the pyramid weighed an average 2.27 metric tons (2.06 short tons) and were quarried at distances of up to 805 km (500 mi) away. It's about 400,000 times as big as The Melbourne Cricket Ground. In other words, 721.9 cubic kilometers is 420,000 times the size of The Melbourne Cricket Ground, and the size of The Melbourne Cricket Ground is 0.0000024 times that amount. (a.k.a. MCG, a.k.a. "The G") (Yarra Park, melbourne, Victoria, Australia) (internal volume)The MCG has an internal volume of approximately 0.0017 cubic kilometers. The first cricket game held on the site of the MCG was in 1853 when the Melbourne Cricket Club was granted permission to a roughly 0.04 sq. km (10-acre) area to be used "for cricket and no other purpose." It's about 600,000 times as big as The Houston Astrodome. In other words, the size of The Houston Astrodome is 0.0000017 times 721.9 cubic kilometers. (a.k.a. Reliant Astrodome, a.k.a. Astrodome, a.k.a. Harris County Domed Stadium) (Houston, Texas)The Reliant Astrodome measures 0.0012 cubic kilometers in total volume. Until its renovation in 1988, Roy "The Judge" Hofheinz, the franchise owner of the Houston Colt .45s (later the Houston Astros) and one of the Astrodome's developers, had a private 966 sq. m (10,400 sq. ft) apartment in the facility.