In the second half of the 20th century much progress was made in increasing the accuracy of measurements of the speed of light, first by cavity resonance techniques and later by laser interferometer techniques. These were aided by new, more precise, definitions of the metre and second. In 1950, Louis Essen determined the speed as 299792.51 km/s, using cavity resonance. This value was adopted by the 12th General Assembly of the Radio-Scientific Union in 1957. In 1960, the metre was redefined in terms of the wavelength of a particular spectral line of krypton-86, and, in 1967, the second was redefined in terms of the hyperfine transition frequency of the ground state of caesium-133.
In 1972, using the laser interferometer method and the new definitions, a group at the US National Bureau of Standards in Boulder, Colorado determined the speed of light in vacuum to be c = 299792456.21.1 m/s. This was 100 times less uncertain than the previously accepted value. The remaining uncertainty was mainly related to the definition of the metre. As similar experiments found comparable results for c, the 15th General Conference on Weights and Measures in 1975 recommended using the value 299792458 m/s for the speed of light.
Sulawesi is part of Wallacea, meaning that it has a mix of both Asian and Australasian species. There are 8 national parks on the island, of which 4 are mostly marine. The parks with the largest terrestrial area are Bogani Nani Wartabone with 2,871 km2 and Lore Lindu National Park with 2,290 km2. Bunaken National Park which protects a rich coral ecosystem has been proposed as an UNESCO World Heritage Site.
Mainland Southeast Asia, also known historically as Indochina, comprising Vietnam, Laos, Cambodia, Thailand, Myanmar (Burma), and (West) Malaysia.
Maritime Southeast Asia, also known historically as the East Indies comprising Indonesia, (East) Malaysia, Singapore, Philippines, East Timor, Brunei, Christmas Island, Andaman and Nicobar Islands, and Cocos (Keeling) Islands.
Most countries in the region enjoy national autonomy. Democratic forms of government and the recognition of human rights are taking root. ASEAN provides a framework for the integration of commerce, and regional responses to international concerns.
Conflicting claims over the Spratly Islands are made by Brunei, China, Malaysia, Philippines, Taiwan, and Vietnam.
In modern times, the Javanese are the largest ethnic group in Southeast Asia, with more than 100 million people, mostly concentrated in Java, Indonesia. In Burma, the Burmese account for more than two-thirds of the ethnic stock in this country, while ethnic Thais and Vietnamese account for about four-fifths of the respective populations of those countries. Indonesia is clearly dominated by the Javanese and Sundanese ethnic groups, while Malaysia is split between half Malays and one-quarter Chinese. Within the Philippines, the Visayan (mainly Cebuanos and Hiligaynons), Tagalog, Ilocano and Bicolano groups are significant.