Hawaii is the newest of the 50 U.S. states, and is the only state made up entirely of islands. It is located on an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of Australia. The state was admitted to the Union on August 21, 1959. Its capital is Honolulu on the island of Oʻahu. The most recent census estimate puts the state's population at 1,283,388. The state encompasses nearly the entire volcanic Hawaiian Island chain, which comprises hundreds of islands spread over 1,500 miles (2,400 km). At the southeastern end of the archipelago, the eight "main islands" are (from the northwest to southeast) Niʻihau, Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Kahoʻolawe, Maui, and Hawaiʻi. The last is by far the largest, and is often called the "Big Island" or "Big Isle" to avoid confusion with the state as a whole. This archipelago is physiographically and ethnologically part of the Polynesian subregion of Oceania.