text:
Chinatown

Chinatown is the catch-all name for an ethnic enclave of Chinese people located outside Greater China, most often in an urban setting. Areas known as "Chinatown" exist throughout the world, including Europe, Asia, Africa, Oceania, and the Americas.

The development of most Chinatowns typically resulted from human migration to an area without any or with few Chinese residents. Binondo in Manila, established in 1594, is recognized as the world's oldest Chinatown. Notable early examples outside Asia include San Francisco's Chinatown in the United States and Melbourne's Chinatown in Australia, which were founded in the early 1850s during the California and Victoria gold rushes, respectively. A more modern example, in Montville, Connecticut, was caused by the displacement of Chinese workers in New York's Manhattan Chinatown following the September 11th attacks in 2001.

Definition
Oxford Dictionaries defines "Chinatown" as "...a district of any non-Asian town, especially a city or seaport, in which the population is predominantly of Chinese origin". However, some Chinatowns may have little to do with China. Some "Vietnamese" enclaves are in fact a city's "second Chinatown", and some Chinatowns are in fact pan-Asian, meaning they could also be counted as a Koreatown or Little India. One example includes Asiatown in Cleveland, Ohio. It was initially referred to as a Chinatown but was subsequently renamed due to the influx of non-Chinese Asian Americans who opened businesses there. Today the district acts as a unifying factor for the Chinese, Taiwanese, Korean, Japanese, Filipino, Indian, Vietnamese, Cambodian, Laotian, Nepalese and Thai communities of Cleveland.

Further ambiguities with the term can include Chinese ethnoburbs which by definition are "...suburban ethnic clusters of residential areas and business districts in large metropolitan areas  An article in The New York Times blurs the line further by categorizing very different Chinatowns such as Chinatown, Manhattan, which exists in an urban setting as "traditional"; Monterey Park's Chinatown, which exists in a "suburban" setting (and labeled as such); and Austin, Texas's Chinatown, which is in essence a "fabricated" Chinese-themed mall. This contrasts with narrower definitions, where the term only described Chinatown in a city setting.

History
Trading centers populated predominantly by Chinese men and their native spouses have long existed throughout Southeast Asia. Emigration to other parts of the world from China accelerated in the 1860s with the signing of the Treaty of Peking (1860), which opened China's borders to free movement. Early emigrants came primarily from the coastal provinces of Guangdong (Canton, Kwangtung) and Fujian (Fukien, Hokkien) in southeastern China – where the people generally speak Toishanese, Cantonese, Hakka, Teochew (Chiuchow) and Hokkien. In the late 19th century and early 20th century, a significant amount of Chinese emigration to North America originated from four counties called Sze Yup, located west of the Pearl River Delta in Guangdong province, making Toishanese a dominant variety of the Chinese language spoken in Chinatowns in Canada and the United States.

As conditions in China have improved in recent decades, many Chinatowns have lost their initial mission, which was to provide a transitional place into a new culture. As net migration has slowed into them, the smaller Chinatowns have slowly decayed, often to the point of becoming purely historical and no longer serving as ethnic enclaves.

In Asia
In the Spanish Philippines, where the oldest surviving Chinatowns are located, the district where Chinese migrants (sangleyes) were required to live is called a parián, which were also often a marketplace for trade goods. Most of them were established in the late 16th century to house Chinese migrants as part of the early Spanish colonial policy of ethnic segregation. There were numerous pariáns throughout the Philippines in various locations, the names of which still survive into modern district names. This include the Parián de Arroceros of Intramuros, Manila (which was eventually moved several times, ending up in Binondo). The term was also carried into Latin America by Filipino migrants. The central market place of Mexico City (now part of Zócalo) selling imported goods from the Manila galleons in the 18th and early 19th centuries was called "Parián de Manila" (or just "Parián").

Along the coastal areas of Southeast Asia, several Chinese settlements existed as early as the 16th century according to Zheng He and Tomé Pires' travel accounts. Melaka during the Portuguese colonial period, for instance, had a large Chinese population in Campo China. They settled down at port towns under the authority's approval for trading. After the European colonial powers seized and ruled the port towns in the 16th century, Chinese supported European traders and colonists, and created autonomous settlements.

Several Asian Chinatowns, although not yet called by that name, have a long history. Those in Nagasaki, Kobe, and Yokohama, Japan, Binondo in Manila, Hoi An and Bao Vinh in central Vietnam all existed in 1600. Glodok, the Chinese quarter of Jakarta, Indonesia, dates to 1740.

Chinese presence in India dates back to the 5th century CE, with the first recorded Chinese settler in Calcutta named Young Atchew around 1780. Chinatowns first appeared in the Indian cities of Kolkata, Mumbai, and Chennai.

The Chinatown centered on Yaowarat Road in Bangkok, Thailand, was founded at the same time as the city itself, in 1782.

Outside of Asia
Many Chinese immigrants arrived in Liverpool in the late 1850s in the employ of the Blue Funnel Shipping Line, a cargo transport company established by Alfred Holt. The commercial shipping line created strong trade links between the cities of Shanghai, Hong Kong, and Liverpool, mainly in the importation of silk, cotton, and tea. They settled near the docks in south Liverpool, this area was heavily bombed during World War II, causing the Chinese community moving to the current location Liverpool Chinatown on Nelson Street.

The Chinatown in San Francisco is one of the largest in North America and the oldest north of Mexico. It served as a port of entry for early Chinese immigrants from the 1850s to the 1900s. The area was the one geographical region deeded by the city government and private property owners which allowed Chinese persons to inherit and inhabit dwellings within the city. Many Chinese found jobs working for large companies seeking a source of labor, most famously as part of the Central Pacific on the Transcontinental Railroad. Since it started in Omaha, that city had a notable Chinatown for almost a century. Other cities in North America where Chinatowns were founded in the mid-nineteenth century include almost every major settlement along the West Coast from San Diego to Victoria. Other early immigrants worked as mine workers or independent prospectors hoping to strike it rich during the 1849 Gold Rush.

Economic opportunity drove the building of further Chinatowns in the United States. The initial Chinatowns were built in the Western United States in states such as California, Oregon, Washington, Idaho, Utah, Colorado and Arizona. As the transcontinental railroad was built, more Chinatowns started to appear in railroad towns such as St. Louis, Chicago, Cincinnati, Pittsburgh and Butte, Montana. Chinatowns then subsequently emerged in many East Coast cities, including New York City, Boston, Philadelphia, Providence and Baltimore. With the passage of the Emancipation Proclamation, many southern states such as Arkansas, Louisiana and Georgia began to hire Chinese for work in place of slave labor.

The history of Chinatowns was not always peaceful, especially when labor disputes arose. Racial tensions flared when lower-paid Chinese workers replaced white miners in many mountain-area Chinatowns, such as in Wyoming with the Rock Springs Massacre. Many of these frontier Chinatowns became extinct as American racism surged and the Chinese Exclusion Act was passed.

In Australia, the Victorian gold rush, which began in 1851, attracted Chinese prospectors from the Guangdong area. A community began to form in the eastern end of Little Bourke Street, Melbourne by the mid-1850s; the area is still the center of the Melbourne Chinatown, making it the oldest continuously occupied Chinatown in a western city (since the San Francisco one was destroyed and rebuilt). Gradually expanding, it reached a peak in the early 20th century, with Chinese business, mainly furniture workshops, occupying a block wide swath of the city, overlapping into the adjacent 'Little Lon' red light district. With restricted immigration it shrunk again, becoming a strip of Chinese restaurants by the late 1970s, when it was celebrated with decorative arches. However, with a recent huge influx of students from mainland China, it is now the center of a much larger area of noodle shops, travel agents, restaurants, and groceries. The Australian gold rushes also saw the development of a Chinatown in Sydney, at first around The Rocks, near the docks, but it has moved twice, first in the 1890s to the east side of the Haymarket area, near the new markets, then in the 1920s concentrating on the west side. Nowadays, Sydney's Chinatown is centered on Dixon Street.

Other Chinatowns in European capitals, including Paris and London, were established at the turn of the 20th century. The first Chinatown in London was located in the Limehouse area of the East End of London at the start of the 20th century. The Chinese population engaged in business which catered to the Chinese sailors who frequented the Docklands. The area acquired a bad reputation from exaggerated reports of opium dens and slum housing.

France received a large settlement of Chinese immigrant laborers, mostly from the city of Wenzhou, in the Zhejiang province of China. Significant Chinatowns sprung up in Belleville and the 13th arrondissement of Paris.

1970s to the present
By the late 1970s, refugees and exiles from the Vietnam War played a significant part in the redevelopment of Chinatowns in developed Western countries. As a result, many existing Chinatowns have become pan-Asian business districts and residential neighborhoods. By contrast, most Chinatowns in the past had been largely inhabited by Chinese from southeastern China.

In 2001, the events of September 11 resulted in a mass migration of about 14,000 Chinese workers from Manhattan's Chinatown to Montville, Connecticut, due to the fall of the garment industry. Chinese workers transitioned to casino jobs fueled by the development of the Mohegan Sun casino.

In 2012, Tijuana's Chinatown formed as a result of availability of direct flights to China. The La Mesa District of Tijuana was formerly a small enclave, but has tripled in size as a result of direct flights to Shanghai. It has an ethnic Chinese population rise from 5,000 in 2009 to roughly 15,000 in 2012, overtaking Mexicali's Chinatown as the largest Chinese enclave in Mexico.

The New York metropolitan area, consisting of New York City, Long Island, and nearby areas within the states of New York, New Jersey, Connecticut, and Pennsylvania, is home to the largest Chinese-American population of any metropolitan area within the United States and the largest Chinese population outside of China, enumerating an estimated 893,697 in 2017, and including at least 12 Chinatowns, including nine in New York City proper alone. Steady immigration from mainland China, both legal and illegal, has fueled Chinese-American population growth in the New York metropolitan area. New York's status as an alpha global city, its extensive mass transit system, and the New York metropolitan area's enormous economic marketplace are among the many reasons it remains a major international immigration hub. The Manhattan Chinatown contains the largest concentration of ethnic Chinese in the Western hemisphere,*
 * and the Flushing Chinatown in Queens has become the world's largest Chinatown.
 * and the Flushing Chinatown in Queens has become the world's largest Chinatown.
 * and the Flushing Chinatown in Queens has become the world's largest Chinatown.
 * and the Flushing Chinatown in Queens has become the world's largest Chinatown.

The COVID-19 pandemic has adversely affected tourism and business in Chinatown, San Francisco and Chinatown, Chicago, Illinois as well as others worldwide.

History

 * People of Fujian province used to move over the South China Sea from the 14th century to look for more stable jobs, in most cases of trading and fishery, and settled down near the port/jetty under approval of the local authority such as Magong (Penghu), Hoian (Vietnam), Songkla (Thailand), Malacca (Malaysia), Banten, Semarang, Tuban (Indonesia), Manila (the Philippines), etc. A large number of this kind of settlements was developed along the coastal areal of the South China Sea, and was called "Campon China" by Portuguese account and "China Town" by English account.

Settlement pattern

 * The settlement was developed along a jetty and protected by Mazu temple, which was dedicated for the Goddess of Sea for safe sailing. Market place was open in front of Mazu temple, and shophouses were built along the street leading from west side of the Mazu temple. At the end of the street, Tudigong (Land God) temple was placed. As the settlement prospered as commercial town, Kuan Ti temple would be added for commercial success, especially by people from Hong Kong and Guangdong province. This core pattern was maintained even the settlement got expanded as a city, and forms historical urban center of the Southeast Asia.

Characteristics
The features described below are characteristic of many modern Chinatowns.

Demographics
The early Chinatowns such as those in San Francisco and Los Angeles in the United States were naturally destinations for people of Chinese descent as migration were the result of opportunities such as the California Gold Rush and the Transcontinental Railroad drawing the population in, creating natural Chinese enclaves that were almost always 100% exclusively Han Chinese, which included both people born in China and in the enclave, in this case American-born Chinese. In some free countries such as the United States and Canada, housing laws that prevent discrimination also allows neighborhoods that may have been characterized as "All Chinese" to also allow non-Chinese to reside in these communities. For example, the Chinatown in Philadelphia has a sizeable non-Chinese population residing within the community.

A recent study also suggests that the demographic change is also driven by gentrification of what were previously Chinatown neighborhoods. The influx of luxury housing is speeding up the gentrification of such neighborhoods. The trend for emergence of these types of natural enclaves is on the decline (with the exceptions being the continued growth and emergence of newer Chinatowns in Queens and Brooklyn in New York City), only to be replaced by newer "Disneyland-like" attractions, such as a new Chinatown that will be built in the Catskills region of New York. This includes the endangerment of existing historical Chinatowns that will eventually stop serving the needs of Chinese immigrants.

Newer developments like those in Norwich, Connecticut, and the San Gabriel Valley, which are not necessarily considered "Chinatowns" in the sense that they do not necessarily contain the Chinese architectures or Chinese language signs as signatures of an officially sanctioned area that was designated either in law or signage stating so, differentiate areas that are called "Chinatowns" versus locations that have "significant" populations of people of Chinese descent. For example, San Jose, California in the United States has 63,434 people (2010 U.S. Census) of Chinese descent, and yet "does not have a Chinatown". Some "official" Chinatowns have Chinese populations much lower than that.

Town-Scape
Many tourist-destination metropolitan Chinatowns can be distinguished by large red arch entrance structures known in Mandarin Chinese as Paifang (sometimes accompanied by imperial guardian lion statues on either side of the structure, to greet visitors). Other Chinese architectural styles such as the Chinese Garden of Friendship in Sydney Chinatown and the Chinese stone lions at the gate to the Victoria, British Columbia Chinatown are present in some Chinatowns. Mahale Chiniha, the Chinatown in Iran, contains many buildings that were constructed in the Chinese architectural style.

Paifangs usually have special inscriptions in Chinese. Historically, these gateways were donated to a particular city as a gift from the Republic of China and People's Republic of China, or local governments (such as Chinatown, San Francisco) and business organizations. The long-neglected Chinatown in Havana, Cuba, received materials for its paifang from the People's Republic of China as part of the Chinatown's gradual renaissance. Construction of these red arches is often financed by local financial contributions from the Chinatown community. Some of these structures span an entire intersection, and some are smaller in height and width. Some paifang can be made of wood, masonry or steel and may incorporate an elaborate or simple design.

Benevolent and business associations

A major component of many Chinatowns is the family benevolent association, which provides some degree of aid to immigrants. These associations generally provide social support, religious services, death benefits (members' names in Chinese are generally enshrined on tablets and posted on walls), meals, and recreational activities for ethnic Chinese, especially for older Chinese migrants. Membership in these associations can be based on members sharing a common Chinese surname or belonging to a common clan, spoken Chinese dialect, specific village, region or country of origin, and so on. Many have their own facilities.

Some examples include San Francisco's prominent Chinese Consolidated Benevolent Association (中華總會館 Zhōnghuá Zǒng Huìguǎn), aka Chinese Six Companies and Los Angeles' Southern California Teochew Association. The Chinese Consolidated Benevolent Association is among the largest umbrella groups of benevolent associations in the North America, which branches in several Chinatowns. Politically, the CCBA has traditionally been aligned with the Kuomintang and the Republic of China.

The London Chinatown Chinese Association is active in Chinatown, London. Chinatown, Paris has an institution in the Association des Résidents en France d'origine indochinoise and it servicing overseas Chinese immigrants in Paris who were born in the former French Indochina.

Traditionally, Chinatown-based associations have also been aligned with ethnic Chinese business interests, such as restaurant, grocery, and laundry (antiquated) associations in Chinatowns in North America. In Chicago's Chinatown, the On Leong Merchants Association was active.

English
Although the term "Chinatown" was first used in Asia, it is not derived from a Chinese language. Its earliest appearance seems to have been in connection with the Chinese quarter of Singapore, which by 1844 was already being called "China Town" or "Chinatown" by the British colonial government. This may have been a word-for-word translation into English of the Malay name for that quarter, which in those days was probably "Kampong China" or possibly "Kota China" or "Kampong Tionghua/Chunghwa/Zhonghua".

The first appearance of a Chinatown outside Singapore may have been in 1852, in a book by the Rev. Hatfield, who applied the term to the Chinese part of the main settlement on the remote South Atlantic island of St. Helena. The island was a regular way-station on the voyage to Europe and North America from Indian Ocean ports, including Singapore.

One of the earliest American usages dates to 1855, when San Francisco newspaper The Daily Alta California described a "pitched battle on the streets of [SF's] Chinatown". Other Alta articles from the late 1850s make it clear that areas called "Chinatown" existed at that time in several other California cities, including Oroville and San Andres. By 1869, "Chinatown had acquired its full modern meaning all over the U.S. and Canada. For instance, an Ohio newspaper wrote: "From San Diego to Sitka..., every town and hamlet has its 'Chinatown'."

In British publications before the 1890s, "Chinatown" appeared mainly in connection with California. At first, Australian and New Zealand journalists also regarded Chinatowns as Californian phenomena. However, they began using the term to denote local Chinese communities as early as 1861 in Australia and 1873 in New Zealand. In most other countries, the custom of calling local Chinese communities "Chinatowns" is not older than the twentieth century.

Several alternate English names for Chinatown include China Town (generally used in British and Australian English), The Chinese District, Chinese Quarter and China Alley (an antiquated term used primarily in several rural towns in the western United States for a Chinese community; some of these are now historical sites). In the case of Lillooet, British Columbia, Canada, China Alley was a parallel commercial street adjacent to the town's Main Street, enjoying a view over the river valley adjacent and also over the main residential part of Chinatown, which was largely of adobe construction. All traces of Chinatown and China Alley there have disappeared, despite a once large and prosperous community.

In Chinese
In Chinese, Chinatown is usually called 唐人街, in Cantonese Tong jan gai, in Mandarin Tángrénjiē, in Hakka Tong ngin gai, and in Toisan Hong ngin gai, literally meaning "Tang people's street(s)". The Tang dynasty was a zenith of the Chinese civilization, after which some Chinese call themselves. Some Chinatowns are indeed just one single street, such as the relatively short Fisgard Street in Victoria, British Columbia, Canada.

A more modern Chinese name is 華埠 (Cantonese: Waa Fau, Mandarin: Huábù) meaning "Chinese City", used in the semi-official Chinese translations of some cities' documents and signs. Bù, pronounced sometimes in Mandarin as fù, usually means seaport; but in this sense, it means city or town. Tong jan fau (唐人埠 "Tang people's town") is also used in Cantonese nowadays. The literal word-for-word translation of Chinatown—Zhōngguó Chéng (中國城) is also used, but more frequently by visiting Chinese nationals rather than immigrants of Chinese descent who live in various Chinatowns.

Chinatowns in Southeast Asia have unique Chinese names used by the local Chinese, as there are large populations of people who are Overseas Chinese, living within the various major cities of Southeast Asia. As the population of Overseas Chinese, is widely dispersed in various enclaves, across each major Southeast Asian city, specific Chinese names are used instead.

For example, in Singapore, where 2.8 million ethnic Chinese constitute a majority 74% of the resident population, the Chinese name for Chinatown is Niúchēshǔi (牛車水, Hokkien POJ: Gû-chia-chúi), which literally means "ox-cart water" from the Malay 'Kreta Ayer' in reference to the water carts that used to ply the area. The Chinatown in Kuala Lumpur, Malaysia, (where 2 million ethnic Chinese comprise 30% of the population of Greater Kuala Lumpur ) while officially known as Petaling Street (Malay: Jalan Petaling), is referred to by Malaysian Chinese by its Cantonese name ci4 cong2 gaai1 (茨廠街, pinyin: Cíchǎng Jiē), literally "tapioca factory street", after a tapioca starch factory that once stood in the area. In Manila, Philippines, the area is called Mínlúnluò Qū 岷倫洛區, literally meaning the "Mín and Luò Rivers confluence district" but is actually a transliteration of the local term Binondo and an allusion to its proximity to the Pasig River.

Other languages
In Philippine Spanish, the term used for Chinatown districts is parián, the etymology of which is uncertain. In the rest of the Spanish Empire, the Spanish-language term is usually barrio chino (Chinese neighborhood; plural: barrios chinos), used in Spain and Latin America. (However, barrio chino or its Catalan cognate barri xinès do not always refer to a Chinese neighborhood: these are also common terms for a disreputable district with drugs and prostitution, and often no connection to the Chinese.).

In Portuguese, Chinatown is often referred to as Bairro chinês (the Chinese Neighbourhood; plural: bairros chineses).

In Francophone regions (such as France and Quebec), Chinatown is often referred to as le quartier chinois (the Chinese Neighbourhood; plural: les quartiers chinois). The most prominent Francophone Chinatowns are located in Paris and Montreal.

The Vietnamese term for Chinatown is Khu người Hoa (Chinese district) or phố Tàu (Chinese street). Vietnamese language is prevalent in Chinatowns of Paris, Los Angeles, Boston, Philadelphia, Toronto, and Montreal as ethnic Chinese from Vietnam have set up shop in them.

In Japanese, the term "chūkagai" (中華街, literally "Chinese Street") is the translation used for Yokohama and Nagasaki Chinatown.

In Indonesia, chinatown is known as Pecinan, a shortened term of pe-cina-an, means everything related to the Chinese people. Most of these pecinans usually located in Java.

Some languages have adopted the English-language term, such as Dutch and German.

Africa
There are three noteworthy Chinatowns in Africa located in the coastal African nations of Madagascar, Mauritius and South Africa. South Africa has the largest Chinatown and the largest Chinese population of any African country and remains a popular destination for Chinese immigrants coming to Africa. Derrick Avenue in Cyrildene, Johannesburg, hosts South Africa's largest Chinatown.

America
In the Americas, which includes North America, Central America and South America, Chinatowns have been around since the 1800s. The most prominent ones exist in the United States and Canada in New York, Boston, San Francisco, Chicago, Toronto and Vancouver. The New York City metropolitan area is home to the largest ethnically Chinese population outside of Asia, comprising an estimated 893,697 uniracial individuals as of 2017, including at least 12 Chinatowns – six (or nine, including the emerging Chinatowns in Corona and Whitestone, Queens, and East Harlem, Manhattan) in New York City proper, and one each in Nassau County, Long Island; Edison, New Jersey; and Parsippany-Troy Hills, New Jersey, not to mention fledgling ethnic Chinese enclaves emerging throughout the New York City metropolitan area. San Francisco, a Pacific port city, has the oldest and longest continuous running Chinatown in the Western Hemisphere. In Canada, The Greater Toronto and Hamilton Area is home to the 2nd largest ethnically Chinese population outside of Asia, comprising 694,970 individuals as of the 2021 Census. Vancouver's Chinatown is the country's largest.

The oldest Chinatown in the Americas is in Mexico City and dates back to at least the early 17th century. Since the 1970s, new arrivals have typically hailed from Hong Kong, Macau, and Taiwan. Latin American Chinatowns may include the descendants of original migrants – often of mixed Chinese and Latin parentage – and more recent immigrants from East Asia. Most Asian Latin Americans are of Cantonese and Hakka origin. Estimates widely vary on the number of Chinese descendants in Latin America. Notable Chinatowns also exist in Chinatown, Lima, Peru.

In Brazil, the Liberdade neighborhood in São Paulo has, along with a large Japanese community, an important Chinese community. There is a project for a Chinatown in the Mercado neighborhood, close to the Municipal Market and the commercial Rua 25 de Março.

Asia
Chinatowns in Asia are widespread with a large concentration of overseas Chinese in East Asia and Southeast Asia and ethnic Chinese whose ancestors came from southern China – particularly the provinces of Guangdong, Fujian, and Hainan – and settled in countries such as Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Singapore, the Philippines, Thailand, and Vietnam centuries ago—starting as early as the Tang dynasty, but mostly notably in the 17th through the 19th centuries (during the reign of the Qing dynasty), and well into the 20th century. Today the Chinese diaspora in Asia is largely concentrated in Southeast Asia however the legacy of the once widespread overseas Chinese communities in Asia is evident in the many Chinatowns that are found across East Asia, South Asia, and Southeast Asia.

Vietnam houses the largest Chinatown by size in Ho Chi Minh City (formerly Saigon).

Australia and Oceania
The Chinatown of Melbourne lies within the Melbourne central business district and centers on the eastern end of Little Bourke Street. It extends between the corners of Swanston and Exhibition Streets. Melbourne's Chinatown originated during the Victorian gold rush in 1851, and is notable as the oldest Chinatown in Australia. It has also been claimed to be the longest continuously running Chinese community outside of Asia, but only because the 1906 San Francisco earthquake all but destroyed the Chinatown in San Francisco in California.

Sydney's main Chinatown centers on Sussex Street in the Sydney downtown. It stretches from Central Station in the east to Darling Harbour in the west, and is Australia's largest Chinatown.

The Chinatown of Adelaide was originally built in the 1960s and was renovated in the 1980s. It is located near Adelaide Central Market and the Adelaide Central bus station.

Chinatown Gold Coast is a precinct in the Central Business District of Southport, Queensland, that runs through Davenport Street and Young Street. The precinct extends between Nerang Street in the north and Garden Street/Scarborough Street east-west. Redevelopment of the precinct was established in 2013 and completed in 2015 in time for Chinese New Year celebrations.

There are additional Chinatowns in Brisbane, Perth, and Broome in Australia.

Europe
Several urban Chinatowns exist in major European capital cities. There is Chinatown, London, England as well as major Chinatowns in Birmingham, Liverpool, Newcastle, and Manchester. Berlin, Germany has one established Chinatown in the area around Kantstrasse of Charlottenburg in the West. Antwerp, Belgium has also seen an upstart Chinese community, that has been recognized by the local authorities since 2011. The city council of Cardiff has plans to recognize the Chinese Diaspora in the city.

The Chinatown in Paris, located in the 13th arrondissement, is the largest in Europe, where many Vietnamese – specifically ethnic Chinese refugees from Vietnam – have settled and in Belleville in the northeast of Paris as well as in Lyon. In Italy, there is a Chinatown in Milan between Via Luigi Canonica and Via Paolo Sarpi and others in Rome and Prato. In the Netherlands, Chinatowns exist in Amsterdam, Rotterdam and the Hague.

In the United Kingdom, several exist in Birmingham, Liverpool, London, Manchester and Newcastle Upon Tyne. The Chinatown in Liverpool is the oldest Chinese community in Europe. The Chinatown in London was established in the Limehouse district in the late 19th century. The Chinatown in Manchester is located in central Manchester.

In popular culture
Chinatowns have been portrayed in various films including The Joy Luck Club, Big Trouble in Little China, Year of the Dragon, Flower Drum Song, The Lady from Shanghai and Chinatown. Within the context of the last film "Chinatown" is used primarily as an extended metaphor for any situation in which an outside entity seeks to intervene without having the local knowledge required to understand the consequences of that intervention. The neighborhood or district is often associated with being outside the normal rule of law or isolated from the social norms of the larger society.

Chinatowns have also been mentioned in the song "Kung Fu Fighting" by Carl Douglas whose song lyrics says "...There was funky China men from funky Chinatown..."

The martial arts actor Bruce Lee is well known as a person who was born in the Chinatown of San Francisco. Other notable Chinese Americans such as politician Gary Locke and NBA player Jeremy Lin grew up in suburbs with lesser connections to traditional Chinatowns. Neighborhood activists and politicians have increased in prominence in some cities, and some are starting to attract support from non-Chinese voters.

Some notable temples in Chinatowns worldwide

 * San Francisco's Chinatown – Tin How Temple (天后古廟), Ma-Tsu Temple (美國舊金山媽祖廟朝聖宮)
 * Los Angeles Chinatown – Thien Hau Temple (天后宮)
 * Yokohama Chinatown – Yokohama Ma Zhu Miao (横濱媽祖廟)
 * Bangkok Chinatown – Leng Buai Ia Shrine (龍尾古廟), Wat Bamphen Chin Phrot (永福寺) & Wat Mangkon Kamalawat (龍蓮寺)
 * Yangon Chinatown – Kheng Hock Keong (慶福宮) & Guanyin Gumiao Temple (觀音古廟)
 * Jakarta Chinatown – Kim Tek Ie Temple (金德院)
 * Kuala Lumpur Chinatown – Sin Sze Si Ya Temple (仙四師爺廟)
 * Malacca Chinatown – Cheng Hoon Teng Temple (青云亭)
 * Terengganu Chinatown – Ho Ann Kiong Temple (护安宫) & Tian Hou Gong Temple (天后宮)
 * Davao Chinatown – Lon Wa Buddhist Temple (龙华寺)
 * Chinatown and Malaytown in Kedah
 * Gaya Street, Kota Kinabalu
 * Chinatown, Kuching

title: Chinatown


text:
Skateboarding trick

A skateboarding trick, or simply a trick, is a maneuver performed by manipulating a skateboard, usually with one's feet, in a specific way to achieve the desired outcome – the trick.

History
Though skateboards emerged in the 1900s, skateboarding tricks like the ones done today did not appear until decades later. In the 1970s and earlier, the most common tricks were "2D" freestyle types such as manuals and pivots. Only later in the 1980s and early 1990s were common modern-day tricks like the ollie and heel-flip invented by Alan Gelfand and Rodney Mullen, setting the stage for other aerial tricks. The invention of these tricks changed the skateboarding lifestyle for many years to come.

Ollie

An ollie is a jump where the front wheels leave the ground first. This motion is attained with a snap of the tail (from the back foot) and sliding one's front foot forward to reach any altitude. A lot of technical tricks transpire from this element (e.g. the kickflip, heelflip, 360-flip). A nollie is when the back wheels leave the ground first by snapping the nose of the board, with the back foot sliding towards the tail. There is also a switch ollie, which is simply an ollie in switch stance position. The switch stance position is the opposite position of how the rider would normally ride.

Grabs
A grab involves floating in the air, while using either hand to hold the board against the feet or keeping constant and careful pressure on the board with the feet to keep it from floating away. The Indy grab usually combines rotation with different grabs. This class of tricks was first popularized when Tony Hawk became famous for his frontside airs in empty swimming pools in the late 1970s and has expanded to include the bulk of skateboarding tricks to this day, including the ollie and all of its variations. The 900 and 1080 fall under the class of aerials, though these are commonly confused with aerial grabs.

Flip tricks

Flip tricks are a subset of aerials which are all based on the ollie. An example is the kickflip, the most widely known and performed flip trick. The board can be spun around many different axes as part of a flip trick, thus combining several rotations into one trick. These tricks are undoubtedly most popular among street skateboarding purists, although skaters with other styles perform them as well. The famous placing of the board on the feet and then jumping was created in 1987 by Nathan Lipor. Combining spins and flips is extremely popular in today's culture. A common trick in skateboarding lines is a 360 flip, or tre flip. A 360 flip is the combination of a skateboard spinning 360 degrees and a kickflip. There are also double kickflips and triple kickflips, which are very difficult.

Freestyle
Freestyle skateboarding tricks are tricks specifically associated with freestyle skateboarding. They are part of the building blocks and some of the most important reference points for tricks which have evolved to form street skateboarding.

Slides and grinds

Slides and grinds involve getting the board up on some type of ledge, rail, or coping and sliding or grinding along the board or trucks, respectively. When it is primarily the board which is contacting the edge, it is called a slide; when it is the truck, it is a grind. Grinding and sliding skateboards started with sliding the board on parking blocks and curbs, then extended to using the coping on swimming pools, then stairway handrails, and has now been expanded to include almost every possible type of edge. Grinds and slides on street environments were brought to mainstream skateboarding by professional skateboarders Natas Kaupas and Mark Gonzales.

Manuals
A manual is a balancing trick where a skateboarder balances on either the front two or rear two wheels, without the other two wheels or any other part of the skateboard touching the ground for the entire duration of the trick. The trick is often performed at speed and technical skateboarders such as Daewon Song are renowned for performing tricks such as the kickflip both in and out of the trick, whilst also simultaneously doing so up onto, over and off ledges, blocks, benches and other street obstacles.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Skateboarding trick


text:
Photosphere

The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately $2/3$, or equivalently, a depth from which 50% of light will escape without being scattered.

A photosphere is the region of a luminous object, usually a star, that is transparent to photons of certain wavelengths.

Etymology
The term photosphere is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to it being a spherical surface that is perceived to emit light.

Temperature
The surface of a star is defined to have a temperature given by the effective temperature in the Stefan–Boltzmann law. Stars, except neutron stars, have no solid or liquid surface. Therefore, the photosphere is typically used to describe the Sun's or another star's visual surface.

Composition of the Sun
The Sun is composed primarily of the chemical elements hydrogen and helium; they account for 74.9% and 23.8%, respectively, of the mass of the Sun in the photosphere. All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant.

Sun

The Sun's photosphere has a temperature between 4400 and 6600 K (with an effective temperature of 5772 K) and a density of about 3 kg/m3; increasing with depth into the sun. Other stars may have hotter or cooler photospheres. The Sun's photosphere is 100–400 kilometers thick.

Photospheric phenomena
In the Sun's photosphere, the most ubiquitous phenomena are granules—convection cells of plasma each approximately 1000 km in diameter with hot rising plasma in the center and cooler plasma falling in the spaces between them, flowing at velocities of 7 km/s. Each granule has a lifespan of only about twenty minutes, resulting in a continually shifting "boiling" pattern. Grouping the typical granules are supergranules up to 30,000 km in diameter with lifespans of up to 24 hours and flow speeds of about 500 m/s, carrying magnetic field bundles to the edges of the cells. Other magnetically related phenomena in the Sun's photosphere include sunspots and solar faculae dispersed between granules. These features are too fine to be directly observed on other stars; however, sunspots have been indirectly observed, in which case they are referred to as starspots.

title: Photosphere


text:
User:Nezumi~enwiki

Hi

I am a some-time university teacher and political activist/greeny type from Wellington, New Zealand. I have recently joined Wikipedia and am still getting the hang of how it works, so as yet haven't contributed anything. I am currently planning contributions on the Green Party of Aotearoa/New Zealand and animal rights.

Welcome to the 'pedia! What's going on with Australia and New Zealand? You must be the 5th Kiwi I welcomed aboard in the last two weeks (only can remember 1 Brit I welcomed during that time and about the same number of Americans as Kiwis). I forgot to let the others now about listing their names on the Wikipedians/New Zealand page. Oh well, at least I remembered to tell you. Hope you like the place and decide to stay. Cheers! --User:maveric149 (an American who is beginning to feel outnumbered by Kiwi and Aussie wikipedians -- must be a conspiracy :)

title: User:Nezumi~enwiki


text:
Boardsport

Boardsports are active outdoor sports that are played with some sort of board as the primary equipment. These sports take place on a variety of terrains, from paved flat-ground and snow-covered hills to water and air. Most boardsports are considered action sports or extreme sports, and thus often appeal to youth. Some board sports were marginalized in the past. However, many board sports are gaining mainstream recognition, and with this recognition, they have enjoyed wider broadcast, sponsorship and inclusion in institutional sporting events, including the Olympic Games.

Surfing is the first known boardsport, originating from Polynesian culture. Skateboarding was then invented by surfers looking to "surf" on land. It is hard to estimate when most boardsports were "invented" because people have been making homemade versions throughout history. For example, it is not hard to conceive of a person, who is familiar with the concept of skiing or sledding, standing sideways on a plank of wood and riding down a snow-covered slope. M.J. "Jack" Burchett is credited with first doing this in 1929, using horse reins and clothesline to secure his feet on the plank of wood. Most boardsports have similar, equally unknown origins.

Using data collected in the past decade, it is estimated there are 18-50 million skateboarders, 5-25 million surfers, and 10-20 million snowboarders in the world. Approximately 100 million people participate in boardsports worldwide.

Classifications
There are a variety of board sports, which are characterized by terrain: Surf, Snow, Wake, Skate are the primary.

Water

 * Surfing: The grandfather of all board sports, surfing is a surface water sport that involves the participant being carried by a breaking wave.
 * Stand Up Paddle Surfing (SUP):A variant of surfing where one always a stands up on the board and propels oneself by a one-bladed paddle, without lying down on the board. Although originally the goal was to catch and surf the waves, a racing modality has emerged with similarities to kayaking.
 * Skimboarding (1930s) :A discipline of surfing involving riding a board on wet sand or shallow water. A predominantly recreational activity that has evolved into a highly competitive water sport.
 * Windsurfing (1970) : Also known as sailboarding. A water sport involving travel over water on a small 2–4.7 metre board powered by wind acting on a single sail. The sail is connected to the board by a flexible joint
 * Bodyboarding (1971) : Wave riding consisting of a small, roughly rectangular piece of foam, shaped to a hydrodynamic form. The bodyboard is ridden predominantly lying down, (or 'prone'). It can also be ridden in a half-standing stance (known as 'dropknee') or can even be ridden standing up.
 * Kneeboarding (1973) :A discipline of surfing where the rider paddles on his belly into a wave on a kneeboard, then rides the wave face typically on both knees.
 * Riverboarding (1978) : A boardsport in which the participant is prone on the board with fins on his/her feet for propulsion and steering.
 * Wakeboarding (1983) : A surface watersport created from a combination of water skiing, snow boarding and surfing techniques. As in water skiing, the rider is towed behind a boat, or a cable skiing setup.
 * Skurfing (1984) :Another fast growing boardsport is skurfing a mix of surfing and more conventional water sports in which the participant is towed behind the boat.
 * Flowriding (1991) : Similar to surfing but done on a man-made artificial sheet wave.
 * Wakeskating (1990s) :A rider is pulled behind a boat on a wakeskate which is smaller than a wakeboard and has no bindings with a foam or griptape surface.
 * Kitesurfing (1996) : Also known as kiteboarding. Boards similar to those known from windsurfing or wakeboarding are propelled by an inflatable or foil power kite, allowing for high speeds and high jumps. Other variations are to use a wheeled board or buggy on land, or skis or a snowboard on snow.
 * Wakesurfing (1997) : A rider is pulled behind a boat on a mini surfboard and can ride the boat's wake with no rope.

Paved surface

 * Skateboarding (1950) : Uses a board mounted on wheels, and often ridden on a half-pipe, in urban settings, or emptied specially built swimming pools.
 * Longboarding (1970s) : Similar to freeboarding but with long skateboards that come in different shapes and sizes, longboarding is mostly a racing sport but there are many other styles as well.
 * Snakeboard (1989) : Similar to skateboarding, but also influenced heavily by snowboarding.
 * Freestyle scootering (1996) : an action sport which involves using scooters to perform freestyle tricks, in a manner similar to skateboarding and BMX freestyle.
 * Carveboarding : A board that has wheels similar to a car except smaller, it turns better than most boards on four wheels, its main purpose is to cruise and carve, it can turn 65 degrees, and has spring-loaded trucks that are almost as unique as a flowboards trucks.
 * Freeboarding: Often said to be the board whose feel is the most similar to snowboarding. There are two extra castor wheels in the middle of the base that are somewhat lower than the other four. This allows the rider to distribute his weight to only one "edge", as in snowboarding. This gives the rider the ability to slide, an ability no other land board has besides the longboard.
 * Caster board : Two narrow platforms known as "decks" are adjoined by a rubber or aluminium coated metal beam that houses a strong spring. Each truck has one wheel that is connected to the board in such a way that each wheel can rotate independently. Both wheels are mounted on slants that measure around 30° in angle, facing away from the front of the board. Similar to Vigorboard (2003) : Constructed from two platforms, each supported by a single caster with a single wheel giving the board a total of two wheels. the two platforms are connected by heavy metal torsion bar that enables the board to twist in the centre.
 * Street Skurfing : Similar to Caster board, but the rider can move both feet independently.
 * Freeline skates (2000's) : A pair of skates designed to give the feeling of skateboarding, snowboarding, surfing, and inline skates all in one. Freeline Skates are extremely portable, making them the smallest and lightest form of transportation. See also Street Skurfing.
 * Street surfing : A split deck board connected by a spring rod to allow each half of the board to twist independently from the other, each side only having 1 caster wheel, allowing for tight maneuvers and self propulsion.
 * On-shore boards: A type of board that has four inline wheels and four in the back (two on each side) and is deeply concave in the front.
 * T-boarding :A skateboard deck with two wheels that can spin 360 degrees.

Off-paved surface

 * Land windsurfing: A sport similar to traditional windsurfing that is performed on land rather than water. A four-wheeled deck, similar to a mountain board or skateboard deck, is commonly used in conjunction with a mast and sail in order to project the board across land.
 * Mountainboarding (1992) : Similar to snowboarding, but on snowless peaks (in between winter seasons). The board is wider and sturdier. Mountainboarding is similar to skateboarding in the way that mountainbiking is similar to regular biking.
 * Kite landboarding: Similar to Kite Surfing but the kite is used to pull the rider along flat ground (often a hard packed sandy beach) on a mountainboard

Snow

 * Snowboarding (1977) :A cross between skateboarding and skiing, the board medium is snow, although the condition of the snow can have a major impact on snowboarding style and technique. The four subcategories are freeride, freestyle, alpine and powder.
 * Snowskating (1998) :This is similar to snowboarding but there are no bindings used. Instead the snow skate has a foam grip similar to griptape, enabling you to do skateboard style tricks. There are four main types of snowskates: Single deck (a skateboard-deck-like platform made out of either wood and/or plastic; Bilevel (similar to a skate board but, instead of trucks and wheels, a small ski with metal edges called a subdeck is used with special trucks to be used on a ski hill); 4x4 (a skateboard but the wheels are replaced by very small skis); Powderskate (can either be like a Bilevel snowskate or a single deck snowskate but longer and wider).
 * Snowkiting: This is when a kite is used to pull a snowboarder along.

Sand

 * Sandboarding: A recreational activity similar to snowboarding that takes place on sand dunes rather than snow-covered hills.

Air

 * Skysurfing: A kind of skydiving in which the skydiver wears a board attached to their feet and performs surfing-style aerobatics during freefall.

title: Boardsport


text:
Water skiing

Water skiing (also waterskiing or water-skiing) is a surface water sport in which an individual is pulled behind a boat or a cable ski installation over a body of water, skimming the surface on two skis or one ski. The sport requires sufficient area on a stretch of water, one or two skis, a tow boat with tow rope, two or three people (depending on local boating laws), and a personal flotation device. In addition, the skier must have adequate upper and lower body strength, muscular endurance, and good balance.

There are water ski participants around the world, in Asia and Australia, Europe, Africa, and the Americas. In the United States alone, there are approximately 11 million water skiers and over 900 sanctioned water ski competitions every year. Australia boasts 1.3 million water skiers.

There are many options for recreational or competitive water skiers. These include speed skiing, trick skiing, show skiing, slaloming, jumping, barefoot skiing and wakeski. Similar, related sports are wakeboarding, kneeboarding, discing, tubing, and sit-down hydrofoil.

Basic technique
Water skiers can start their ski set in one of two ways: wet is the most common, but dry is possible. Water skiing typically begins with a deep-water start. The skier enters the water with their skis on or they jump in without the skis on their feet, having the skis floated to them, and put them on while in the water. Most times it can be easier to put the skis on when they are wet. Once the skier has their skis on they will be thrown a tow rope from the boat, which they position between their skis or, if on only one ski, to the left if right foot forward and to the right if left foot forward. In the deep-water start, the skier crouches down in the water while holding onto the ski rope; they are in a cannonball position with their legs tucked into their chest, with skis pointing towards the sky and approximately 30 cm of the ski out of the water. The skier can also perform a "dry start" by standing on the shore or a pier; however, this type of entry is recommended for professionals only. When the skier is ready (usually acknowledged by them yelling "in gear,": followed by "hit it"), the driver accelerates the boat. As the boat accelerates and takes up the slack on the rope, the skier allows the boat to pull them out of the water by applying some muscle strength to get into an upright body position.

By leaning back and keeping the legs slightly bent, the skis will eventually plane out and the skier will start to glide over the water. The skier turns by shifting weight left or right. The skier's body weight should be balanced between the balls of the feet and the heels. While being towed, the skier's arms should be relaxed but still fully extended so as to reduce stress on the arms. The handle can be held vertically or horizontally, depending on whichever position is more comfortable for the skier.

In addition to the driver and the skier, a third person known as the spotter or the observer should be present. The spotter's job is to watch the skier and inform the driver if the skier falls. The spotter usually sits in a chair on the boat facing backwards to see the skier. The skier and the boat's occupants communicate using hand signals (see the Safety section below).

Water
Water skiing can take place on any type of water – such as a river, lake, or ocean – but calmer waters are ideal for recreational skiing. There should be a 200 ft skiing space and the water should be at least 5 to 6 ft deep. There must be enough space for the water skier to safely "get up", or successfully be in the upright skiing position. Skiers and their boat drivers must also have sufficient room to avoid hazards.Most Competitive skiers ski on man made ski lakes. The first was in Barstow Ca built by Jack Horton in 1969. The Second built by famed water ski magnate Herb O'Brien was built in 1972 in Redmond Washington. Today there are over 384 Man made ski lakes in the US.

Skis
Younger skiers generally start out on children's skis, which consist of two skis tied together at their back and front. These connections mean that less strength is necessary for the child to keep the skis together. Sometimes these skis can come with a handle to help balance the skier as well. Children's skis are short – usually 45 - 60 in long – reflecting the skier's smaller size. Once a person is strong enough to hold the skis together themselves there are various options depending upon their skill level and weight.

Water skiers can use two skis (one on each foot, also called "combo skiing" ) or one ski (dominant foot in front of the other foot, also called "slalom skiing" ). Generally the heavier the person, the bigger the skis will be. Length will also vary based on the type of water skiing being performed; jump skis, for example, are longer than skis used in regular straight-line recreational skiing or competitive slalom and trick skiing. A trick ski is around 40 inches long and wider than combo skis. Again the skier rides it with his or her dominant foot in front. It has no fins which allows for spins to be performed.

Modern water skis have evolved from wooden barrels and snow skis to sophisticated composites of thermoplastics, aluminum, Kevlar, and carbon fiber. These materials make the skis not only high-performing but also sustainable, as manufacturers now use recycled materials to reduce waste and environmental impact. The incorporation of these advanced materials has led to skis that are incredibly strong, lightweight, and flexible, enhancing both performance and durability. Classic water skis are approximately 1.7 meters (5.5 feet) long and 15 centimeters (6 inches) wide, equipped with a stabilizing fin and rubber foot bindings for safety during falls. In contrast, skis used for trick or figure waterskiing are shorter, lack fins for complete rotation capability.

Boat
Competition skiing uses specifically designed towboats. Most towboats have a very small hull and a flat bottom to minimize wake. A true tournament ski boat will have a direct drive motor shaft that centers the weight in the boat for an optimal wake shape. However, some recreational ski boats will have the motor placed in the back of the boat (v-drive), which creates a bigger wake. Permitted towboats used for tournament water skiing are the MasterCraft ProStar 197, MasterCraft ProStar 190, Ski Nautique 200, Malibu Response TXi, and Centurion Carbon Pro. These boats have ability to pull skiers for trick skiing, jumping, and slalom.

Recreational boats can serve as water skiing platforms as well as other purposes such as cruising and fishing. Popular boat types include bowriders, deckboats, cuddy cabins, and jetboats.

The towboat must be capable of maintaining the proper speed. Speeds vary with the skier's weight, experience level, comfort level, and type of skiing. For example, a child on two skis would require speeds of 13 - 16 mph, whereas an adult on one ski might require as high as 36 mph. Barefoot skiing requires speeds of approximately 72 km/h. Competition speeds have a wide range: as slow as 22 km/h up to 58 km/h for slalom water skiing, and approaching 190 km/h in water ski racing.

The boat must be equipped with a ski rope and handle. The tow rope must be sufficiently long for maneuvering, with a recommended length of 75 ft (within tolerance ) although length varies widely depending on the type of water skiing and the skier's skill level. Competition requirements on rope construction have changed over the years, from "quarter-inch polypropylene rope" in 1992 to the 2003 flexibility as long as the same specification is used "for the entire event." The rope and handle are anchored to the boat and played out at the stern. This anchor point on a recreation boat is commonly a tow ring or cleat, mounted on the boat's stern. For more dedicated skiers, a metal ski pylon is placed in the center of the boat in front of the engine to connect the skier. This pylon must be mounted securely, since a skilled slalom skier can put a considerable amount of tension on the ski rope and the pylon.

Safety measures
As water skiing is a potentially dangerous sport, safety is important.

There should be a 200 ft wide skiing space and the water should be at least 5 to 6 ft deep. The towboat should stay at least 100 ft from docks, swim areas, and the shore, and other boats should steer clear of skiers by at least 100 feet. Without proper space and visibility skiing can be extremely dangerous. Skiers should wear a life jacket regardless of swimming ability, although the expectation that all skiers are also competent swimmers is advisable as well. Specially-designed life jackets or ski vests allow movement needed for the sport while still providing floatation for a downed or injured skier. The most common water ski injuries involve the lower legs, such as the knee, because a fall at high speed can create irregular angles of collision between the skier's body and the water surface. Another common cause of injury is colliding with objects on or near the water, like docks.

The tow boat must contain at least two people: a driver and an observer. In most locales, the observer will need to be at least 12 years of age. The driver maintains a steady course, free of obstacles to the skier. The observer continually observes the skier, relays the condition of the skier to the boat driver, and if necessary, raises the "skier down" warning flag, as required, when a skier is in the water, returning to the boat, or in some localities, the entire time the skier is out of the boat. The skier and observer should agree on a set of standard hand-signals for easy communication: stop, speed up, turn, I'm OK, skier in the water, etc.

History
Water skiing was invented in 1922 when Ralph Samuelson used a pair of boards as skis and a clothesline as a towrope on Lake Pepin in Lake City, Minnesota. Samuelson experimented with different positions on the skis for several days until 2 July 1923. Samuelson discovered that leaning backwards in the water with ski tips up and poking out of the water at the tip was the optimal method. His brother Ben towed him and they reached a speed of 20 mph. Samuelson spent 15 years performing shows and teaching water skiing to people in the United States.

Samuelson went through several iterations of equipment in his quest to ski on water. His first equipment consisted of barrel staves for skis. He later tried snow skis, but finally fabricated his own design out of lumber with bindings made of strips of leather. The ski rope was made from a long window sash cord. Samuelson never patented any of his ski equipment.

The first patent for water skis was issued to Fred Waller, of Huntington, NY, on 27 October 1925, for skis he developed independently and marketed as "Dolphin Akwa-Skees." Waller's skis were constructed of kiln-dried mahogany, as were some boats at that time. Jack Andresen patented the first trick ski, a shorter, fin-less water ski, in 1940.

In 1928, Don Ibsen developed his own water skis out in Bellevue, Washington, never having heard of Samuelson or Waller. In 1941, Don Ibsen founded The Olympic Water Ski Club in Seattle, Washington. It was the first such club in America. Ibsen, a showman and entrepreneur, was one of the earliest manufacturers of water skis and was a leading enthusiast and promoter of the sport. In 1983, he was inducted into the Water Ski Hall of Fame in Winter Haven, Florida.

The sport of water skiing remained an obscure activity for several years after 1922, until Samuelson performed water ski shows from Michigan to Florida. The American Water Ski Association formally acknowledged Samuelson in 1966 as the first recorded water skier in history. Samuelson was also the first ski racer, slalom skier, and the first organizer of a water ski show.

Parallel to this, an avid sailor, sportsman and early adopter of water skiing, the young Swedish engineer Gunnar Ljungström (1905–1999) pioneered water skiing in slalom moves from 1929. A demonstrating behind a motorboat was made to the Swedish public at the 100th anniversary of the Royal Swedish Yacht Club in Sandhamn outside Stockholm in 1930.

Water skiing gained international attention in the hands of famed promoter, Dick Pope, Sr., often referred to as the "Father of American Water Skiing" and founder of Cypress Gardens in Winter Haven, Florida. Pope cultivated a distinct image for his theme-park, which included countless photographs of the water skiers featured at the park. These photographs began appearing in magazines worldwide in the 1940s and 1950s, helping to bring international attention to the sport for the first time. He was also the first person to complete a jump on water skis, jumping over a wooden ramp in 1928, for a distance of 25 feet. His son, Dick Pope, Jr., is the inventor of bare-foot skiing. Both men are in the Water Ski Hall of Fame. Today, Winter Haven, Florida, with its famous Chain of Lakes, remains an important city for water skiing, with several major ski schools operating there.

Water skiing has developed over time. Water skiing tournaments and water skiing competitions have been organized. As an exhibition sport, water skiing was included in the 1972 Olympics. The first National Show Ski Tournament was held in 1974, and the first ever National Intercollegiate Water Ski Championships were held in 1979. The Home CARE US National Water Ski Challenge, the first competition for people with disabilities, was organized ten years later.

The first patented design of a water ski which included carbon fiber was that of Hani Audah at SPORT labs in 2001. Its first inclusion in tournament slalom skiing was in 2003.

3-event tournament water skiing
In the United States, there are over 900 sanctioned water ski competitions each summer. Orlando, Florida is considered to be the competitive 3-event waterskiing capital of the world. Competitive water skiing consists of three events: slalom, jump, and trick.

Slalom
In an attempt to become as agile as possible, slalom water skiers use only one ski with feet oriented forward, one in front of the other. Slalom skis are narrow and long, at 57 - 70 in depending on the height and weight of the skier. The two forward-facing bindings vary: they can be made of rubber or thick plastic, and they can be designed more like a snow ski binding or more like a roller blade boot.

Slalom skiing involves a multi-buoy course that the skier must go around in order to complete the pass. A complete slalom water ski course consists of 26 buoys. There are entrance gates at the beginning and end of the course that the skier must go between, and there are 6 turn buoys that the skier must navigate around in a zigzag pattern. The remainder of the buoys are for the driver to ensure the boat goes straight down the center of the course. For a tournament to be sanctioned as 'record capable' by the International Waterski & Wakeboard Federation (IWWF), the entire course must be surveyed prior to competition by a land surveyor to ensure its accuracy. The drivers boat path must be verified as well to ensure that all skiers are getting a fair pull.

Every consecutive pass is harder than the pass before it. When a pass is completed, the boat is sped up by 3 km/h or the rope is shortened by specific increments. The rope is usually not shortened until the maximum speed has been reached for the division, based on the skier's gender and age (55 km/h for women and 58 km/h for men). In a tournament, the boat speeds up or the rope shortens until the skier fails to complete the slalom course by falling, not getting around a buoy, or missing an entrance or exit gate.

A skier's score is based upon the number of successful buoys cleared, the speed of the boat, and the length of the rope. In a tournament, skiers choose the starting boat speed and rope length (with a maximum length of 22.86 m). Professional water skiers will typically start at the max speed of 58 km/h with a rope that has already been shortened to 13 m. The skier with the most buoys wins the competition.

The turn buoys are positioned 11.5 m away from the center of the slalom course. As the rope is shortened beyond that, the skiers are required to use the momentum generated through their turns to swing up on the side of the boat and reach out in order to get their ski around the next buoy. At these rope lengths, the skier's body is experiencing intense isometric contractions and extreme upper body torque with loads of up to 600 kg as they begin accelerating after rounding a turn buoy. Their top speeds will generally be more than double the boat's speed, which means that the Pro men can reach speeds in excess of 116 km/h and each turn will generally generate around 4 g of force. Essentially, slalom water skiers are using their body as a lever, which allows them to withstand loads that would otherwise not be possible for the human body.

Jump
Water ski jumpers use two long skis to ride over a water ski jump in an attempt to travel the longest distance. In a tournament, skiers are given three attempts to hit the ramp. The winner is the skier who travels the farthest calculated distance and successfully rides away. There are no style points, simply distance.

Water ski jumps have specific dimensions and the ramp height is adjustable. Skiers may choose their boat speed and ramp height, although there are maximums based the skier's gender and age. Professional ski jumpers have a maximum boat speed of 58 km/h. The ramp height must be between 5 and 6 ft. As a professional jumper approaches the ramp they will zigzag behind the boat in a series of cuts to generate speed and angle. When the jumper hits the ramp they will generally be going over 112 km/h and the load they have generated on the rope can be over 600 kg.

Trick
The Trick competition has been described as the most technical of the three classic water skiing events.

Trick skiing uses small, oval-shaped or oblong water skis. Beginners generally use two skis while more advanced skiers use one. The shorter, wider Trick ski has a front binding facing forward and a back binding facing at a 45°. It has a smooth bottom that allows it to turn over the surface of the water. According to official 2013 Tournament Rules for 3-event competition in the United States and the Pan-Am Games, skis used in the Tricks event must be a single ski without fins, although molded rails/grooves less than 1/4 in are allowed, as are a foot pad cemented to the ski as a place for the rear foot; in addition, the ski must float with all bindings, fins, etc., installed. The ski's configuration allows the skier to perform both surface and air tricks in quick succession.

In a tournament, skiers are given two 20-second runs during which they perform a series of their chosen tricks. In most cases, one pass is for hand tricks, which includes surface turns, rotations over the wake, and flips. The second pass is for toe tricks, which are done by doing wake turns and rotations with only a foot attaching them to the handle; the foot is either in the toehold part of the handle or, professionally, attached to the rope. The toehold part of the handle does not allow the skier to let go of the handle if they lose their balance and fall into the water, therefore a person in the boat is required to release the rope from the boat using a quick release mechanism installed on the ski pylon. A trick cannot be repeated. Each trick has a point value. A panel of five judges assesses which tricks were completed correctly and assigns that predetermined point value to each successfully completed trick. The skier with the most points wins.

Barefoot water skiing

A barefoot water skier should use a wetsuit instead of a life jacket because the wetsuit covers more of the body in case of a fall at high speed. The wetsuit also allows the skier to do starts in the water where they lie on their back. Unlike a normal life jacket, the "barefoot wetsuit" allows the skier to glide on their back on top of the water once they reach a high enough speed. The barefoot wetsuit is generally thicker in the back, rear, and chest for flotation and impact absorption.

Barefoot skiing requires a higher speed because the skier's feet are smaller than skis, providing less lift. A rule of thumb for barefoot water skiing speed in miles per hour is (M/10)+18=S, where M equals the skier's weight in pounds. In other words, a 175 lb person would have to divide 175/10, which is 17.5; then simply add 17.5+18 which equals 35.5 mph.

Another tool used in barefoot water skiing is the barefoot boom. It provides a stable aluminum bar on the side of the boat where a short rope can be attached or the skier can grip the bar itself. The skier is within earshot of the people in the boat, providing a good platform for teaching. Once the bare footer is good enough, he/she will go behind the boat with a long rope.

A beginner can wear shoes to decrease the necessary speed, lessen foot injury from choppy water, learn better technique, and master the sport.

Show skiing
Show skiing is a type of water skiing where skiers perform tricks somewhat similar to those of gymnasts while being pulled by the boat. Traditional ski show acts include pyramids, ski doubles, freestyle jumping, and swivel skiing. Show skiing is normally performed in water ski shows, with elaborate costumes, choreography, music, and an announcer. Show teams may also compete regionally or nationally. In the US, each team member must be a member of USA Water Ski to compete.

The first organized show occurred in 1928. The bi-annual World Show Ski Championship was inaugurated in September 2012 in Janesville, Wisconsin. Past competition included teams from Australia, Belgium, Canada, China, and the United States.

Freestyle jumping
Freestyle jumping is often related to show skiing. The goal is to go off the jump, perform one of many stunts, and successfully land back on the water. The most common freestyle stunts – in order of usual progression – would be a heli (360°), a flip (forwards), a gainer (a back flip), and a möbius (back flip with 360°).

Ski racing
Water ski racing consists of 1 or 2 skiers per boat who race around a set course behind boats set up for this type of event. It can occur in a 'circle' or lap format type racing or on river courses offering longer distances and higher speeds. Races can be timed events such as 20 minute races and up to 1 hour or on courses where race distance can be over 100 km in length.

Speeds vary by classes but can reach up to 200 km/h. Boats can be inboards or outboards and are generally between 19 and 21 feet in length. Outboards are commonly 300HP and Inboards around 1,300HP (majority are turbocharged).

Current format world championship racing involves men's and women's open (unrestricted), and men's and women formula 2 (limited to single rig, 300 hp outboards, as well as junior classes for under 17's. The World Championships are held every 2 years with the most recent being 2019 in Vichy, France.

Major events include the Southern 80 (Echuca Victoria Australia), the Diamond Race (Viersel Belgium), the Catalina ski race (Long Beach CA United States), and the Bridge to Bridge (Sydney Australia). Races can have anywhere from 10 boats to 150 boats competing (grouped by engine size and age classes).

Disabled
Disabled water skiing uses equipment or other adaptations to allow disabled people to compete in standard 3 event skiing. Seated water skis, special handles, audio slalom gear, and other adaptations are all used for different disabilities.

Criticism
While water skiing is very popular, it is not universally liked. The fast, powerful boats create noise, cause waves which can cause beach erosion, and sometimes hit swimmers, other boats, or marine life. People operating boats may drink alcohol, which increases the chance of accidents. Water skiing is also criticized for air pollution from the boats' engines, and the unnecessary use of fuel (usually gasoline) and the consequent impact to climate change.

title: Water skiing


text:
Eric Heiden

Eric Arthur Heiden (born June 14, 1958) is an American physician and a former long track speed skater, road cyclist and track cyclist. He won an unprecedented five individual gold medals, and set four Olympic records and one world record at the 1980 Winter Olympic Games. Heiden was the most successful athlete at those Olympic Games, single-handedly winning more gold medals than all nations except for the Soviet Union (10) and East Germany (9). He is the most successful Winter Olympian from a single edition of any Winter Olympics. He delivered the Athlete's Oath at those same 1980 Games. His coach was Dianne Holum.

Heiden is an icon in the speed skating community. His victories are significant, as few speed skaters (and athletes in general) have won competitions in both sprint and long-distance events. Heiden is the only athlete in the history of speed skating to have won all five events in a single Olympic tournament and the only one to have won a gold medal in all events. He is considered by some to be the best overall speed skater (short and long distances) in the sport's history. Heiden ranked No. 46 in ESPN's SportsCentury 50 Greatest Athletes of the 20th Century in 1999, the only speed skater to make the list. In 2000, a Dutch newspaper called him the greatest skater ever.

Early life, education and family
Heiden was born in Madison, Wisconsin on June 14, 1958. His father, Jack Heiden, was a longtime orthopedic surgeon in Madison. His sister, Beth Heiden, also became an accomplished cyclist, speed skater and cross-country skier. In their hometown Shorewood Hills, Wisconsin (a suburb of Madison), Eric and his sister Beth were the driving forces behind the creation of the Heiden Haus, a small outpost where local children can warm up after skating or playing hockey on the ice rink (complete with underground clay platform). He graduated from Madison West High School in 1976.

After starting his undergraduate education at the University of Wisconsin–Madison, Heiden transferred to the University of California, San Diego and then to Stanford University in California, earning a B.S. degree in 1984 and an M.D. degree in 1991.

Speed skating
Heiden won the World Junior Speed Skating Championships in 1977 and 1978. During his short speed skating career, Heiden won three World Allround Championships and four World Sprint Championships, becoming the youngest athlete to do so. Three times he broke the world record in the 1000 metres, twice in the 3000 metres, and once each in the 1500 metres and 10000 metres. He also broke the points world record in both allround and the sprinting distances.

Heiden finished his speed skating career by finishing second behind Hilbert van der Duim at the 1980 World Allround Championships in Heerenveen. He stood at the top of the Adelskalender, a ranking system for long-track speed skating, for a record 1,495 days, and he won the Oscar Mathisen Award four times in a row from 1977 until 1980. As of 2024, he still is the only skater who has won the award four times.

He received the 1980 James E. Sullivan Award as the top amateur athlete in the United States. In 1983, he was inducted into the United States Olympic Hall of Fame.

Heiden was elected to the Wisconsin Athletic Hall of Fame in 1990.

World records
Over the course of Heiden's career he skated 15 world records:

Cycling
After his speed-skating career Heiden became a professional cyclist.

Track cycling
As a track cyclist Heiden competed at the 1981 UCI Track Cycling World Championships in Brno, but was not successful. He finished 19th and last in the men's individual pursuit event.

Road bicycle racing
Heiden became a professional racing cyclist. He was one of the first cross-over athletes, becoming a founding member of the 7-Eleven Cycling Team. Together with his former speed skating coach (and ex-bike racer), Jim Ochowicz, he conceived of the idea of a European-style sponsored team for North American riders Heiden won a few American professional races. He finished the 1985 Giro d'Italia and took part in the 1986 Tour de France, although he did not complete the race, crashing on a downhill stretch and suffering a concussion five days from the finish.

Heiden is believed to have recorded one of the fastest times at 14:10 (1986 or 1987) on one of the local benchmark climbs in Woodside, California: Old La Honda Road. In 1985, Heiden won the first U.S. Professional Cycling Championship, becoming the American road race champion.

In 1999, Heiden was inducted into the United States Bicycling Hall of Fame.

Medical career
Heiden completed medical school at Stanford University in 1991, and orthopedic residency training at University of California, Davis, in 1996, then spent a year at a sports medicine clinic in Birmingham, Alabama. He returned to California to practice as an orthopedic surgeon in Sacramento. At that time, he also served as team physician for the NBA's Sacramento Kings and the Sacramento Monarchs of the WNBA. In 2002, 2006, 2010 and 2014 he was team physician for the U.S. Olympic speed skating team. He opened a sports medicine-based practice at The Orthopedic Specialty Hospital (TOSH) in Murray, Utah and expanded Heiden Orthopaedics with an additional office in Park City, Utah.

In 2008, Heiden and Massimo Testa published Faster, Better, Stronger, a book about exercise science and exercise programs.

In 2009, Heiden was one of the team of doctors assisting U.S. speed skater J.R. Celski as the latter recovered from a very bad speed skating crash during the U.S. Olympic trials. Despite cutting himself to the bone and requiring 60 stitches, Celski was able to recover in time for the 2010 Winter Olympics in Vancouver, where he won the bronze medal in both men's 1500 m and 5000 m relay.

Personal life
Heiden met fellow medical student Karen Drews while the two were studying at Stanford, and they married in 1995. Karen is a hand surgeon. They have a daughter, Zoe, born in 2001.

Heiden was offered many sponsorship opportunities after his record-setting performance in the 1980 Winter Olympics, but turned down most of them, saying he had enough money, and preferred the anonymity.

A number of American former gold medal winners, including Heiden, were asked to participate in the ceremonies for the 2002 Winter Olympics held in Salt Lake City, Utah, but Heiden declined after he was passed over for the honor of lighting the Olympic torch. The 1980 U.S. Hockey Team, which won the gold medal at the 1980 games, was given the honor instead. Heiden said in 2009: "I was probably just too stubborn. I figured if they don't appreciate what I did as a skater, if they don't appreciate now what I am doing as a human being, I'd just as soon hang out with my buddies and watch it. I did not mean to slight the Olympic hockey team in any way."

title: Eric Heiden


text:
Cosmological constant

In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: $Λ$), alternatively called Einstein's cosmological constant, is the constant coefficient of a term that Albert Einstein temporarily added to his field equations of general relativity. He later removed it; however, much later it was revived and reinterpreted as the energy density of space, or vacuum energy, that arises in quantum mechanics. It is closely associated with the concept of dark energy.

Einstein originally introduced the constant in 1917 to counterbalance the effect of gravity and achieve a static universe, a notion that was the accepted view at the time. Einstein's cosmological constant was abandoned after Edwin Hubble's confirmation that the universe was expanding. From the 1930s until the late 1990s, most physicists agreed with Einstein's choice of setting the cosmological constant to zero. That changed with the discovery in 1998 that the expansion of the universe is accelerating, implying that the cosmological constant may have a positive value.

Since the 1990s, studies have shown that, assuming the cosmological principle, around 68% of the mass–energy density of the universe can be attributed to so-called dark energy. The cosmological constant $Λ$ is the simplest possible explanation for dark energy, and is used in the current standard model of cosmology known as the ΛCDM model.

According to quantum field theory (QFT), which underlies modern particle physics, empty space is defined by the vacuum state, which is composed of a collection of quantum fields. All these quantum fields exhibit fluctuations in their ground state (lowest energy density) arising from the zero-point energy present everywhere in space. These zero-point fluctuations should act as a contribution to the cosmological constant $Λ$, but when calculations are performed, these fluctuations give rise to an enormous vacuum energy. The discrepancy between theorized vacuum energy from quantum field theory and observed vacuum energy from cosmology is a source of major contention, with the values predicted exceeding observation by some 120 orders of magnitude, a discrepancy that has been called "the worst theoretical prediction in the history of physics!". This issue is called the cosmological constant problem and it is one of the greatest mysteries in science with many physicists believing that "the vacuum holds the key to a full understanding of nature".

History
The cosmological constant was originally introduced in Einstein's 1917 paper entitled “The cosmological considerations in the General Theory of Reality”. Einstein included the cosmological constant as a term in his field equations for general relativity because he was dissatisfied that otherwise his equations did not allow for a static universe: gravity would cause a universe that was initially non-expanding to contract. To counteract this possibility, Einstein added the cosmological constant. However, Einstein was not happy about adding this cosmological term. He later stated that "Since I introduced this term, I had always a bad conscience. ... I am unable to believe that such an ugly thing is actually realized in nature". Einstein's static universe is unstable against matter density perturbations. Furthermore, without the cosmological constant Einstein could have found the expansion of the Universe before Hubble's observations.

In 1929, not long after Einstein developed his static theory, observations by Edwin Hubble indicated that the universe appears to be expanding; this was consistent with a cosmological solution to the original general relativity equations that had been found by the mathematician Friedmann, working on the Einstein equations of general relativity. Einstein reportedly referred to his failure to accept the validation of his equations—when they had predicted the expansion of the universe in theory, before it was demonstrated in observation of the cosmological redshift—as his "biggest blunder".

It transpired that adding the cosmological constant to Einstein's equations does not lead to a static universe at equilibrium because the equilibrium is unstable: if the universe expands slightly, then the expansion releases vacuum energy, which causes yet more expansion. Likewise, a universe that contracts slightly will continue contracting.

However, the cosmological constant remained a subject of theoretical and empirical interest. Empirically, the cosmological data of recent decades strongly suggests that our universe has a positive cosmological constant. The explanation of this small but positive value is a remaining theoretical challenge, the so-called cosmological constant problem.

Some early generalizations of Einstein's gravitational theory, known as classical unified field theories, either introduced a cosmological constant on theoretical grounds or found that it arose naturally from the mathematics. For example, Arthur Eddington claimed that the cosmological constant version of the vacuum field equation expressed the "epistemological" property that the universe is "self-gauging", and Erwin Schrödinger's pure-affine theory using a simple variational principle produced the field equation with a cosmological term.

In 1990s, Saul Perlmutter at Lawrence Berkeley National Laboratory, Brian Schmidt of the Australian National University and Adam Riess of the Space Telescope Science Institute were searching for type Ia supernovas. By that time, they expected to observe the deceleration of the supernovas caused by the gravitation attraction of mass according to Einstein’s gravitational theory. The first reports published in July 1997 from Supernova Cosmology Project used the supernova observation to support such deceleration hypothesis. But soon they found that supernovas were flying away in an accelerating manner. In 1998, both teams announced this surprising result. It implied the Universe is under accelerating expansion. The cosmological constant is needed to explain such acceleration. After this discovery, the cosmological constant was put back to the equation of general relativity.

Sequence of events 1915–1998

 * In 1915, Einstein publishes his equations of general relativity, without a cosmological constant $Λ$.
 * In 1917, Einstein adds the parameter $Λ$ to his equations when he realizes that his theory implies a dynamic universe for which space is a function of time. He then gives this constant a value that makes his Universe model remain static and eternal (Einstein static universe).
 * In 1922, the Russian physicist Alexander Friedmann mathematically shows that Einstein's equations (whatever $Λ$) remain valid in a dynamic universe.
 * In 1927, the Belgian astrophysicist Georges Lemaître shows that the Universe is expanding by combining general relativity with astronomical observations, those of Hubble in particular.
 * In 1931, Einstein accepts the theory of an expanding universe and proposes, in 1932 with the Dutch physicist and astronomer Willem de Sitter, a model of a continuously expanding Universe with zero cosmological constant (Einstein–de Sitter spacetime).
 * In 1998, two teams of astrophysicists, one led by Saul Perlmutter, the other led by Brian Schmidt and Adam Riess, carried out measurements on distant supernovae which showed that the speed of galaxies' recession in relation to the Milky Way increases over time. The universe is in accelerated expansion, which requires having a strictly positive $Λ$. The universe would contain a mysterious dark energy producing a repulsive force that counterbalances the gravitational braking produced by the matter contained in the universe (see Standard cosmological model). For this work, Perlmutter, Schmidt, and Riess jointly received the Nobel Prize in physics in 2011.

Equation
The cosmological constant $Λ$ appears in the Einstein field equations in the form $$R_{\mu \nu} - \tfrac{1}{2} R\, g_{\mu \nu} + \Lambda g_{\mu \nu} = \kappa T_{\mu \nu} ,$$ where the Ricci tensor $R_{μν}$, Ricci scalar $R$ and the metric tensor $g_{μν}$ describe the structure of spacetime, the stress–energy tensor $T_{μν}$ describes the energy density, momentum density and stress at that point in spacetime, and $κ = 8πG/c4$. The gravitational constant $G$ and the speed of light $c$ are universal constants. When $Λ$ is zero, this reduces to the field equation of general relativity usually used in the 20th century. When $T_{μν}$ is zero, the field equation describes empty space (a vacuum).

The cosmological constant has the same effect as an intrinsic energy density of the vacuum, $ρ$$vac$ (and an associated pressure). In this context, it is commonly moved to the right-hand side of the equation using $Λ = κρvac$. It is common to quote values of energy density directly, though still using the name "cosmological constant". The dimension of $Λ$ is generally understood as length$−2$.

Using the values known in 2018 and Planck units for $ΩΛ$ = $0.689$ and the Hubble constant $H$0 = $67.66 (km/s)/Mpc$ = $2.193 s-1$, $Λ$ has the value of $$\begin{align} \Lambda = 3\, \left( \frac{\,H_0\,}{c} \right)^2 \Omega_\Lambda &= 1.1056 \times 10^{-52}\ \text{m}^{-2} \\ &= 2.888 \times 10^{-122} \,l_{\text{P}}^{-2} \end{align}$$ where $l_{\text{P}}$ is the Planck length. A positive vacuum energy density resulting from a cosmological constant implies a negative pressure, and vice versa. If the energy density is positive, the associated negative pressure will drive an accelerated expansion of the universe, as observed. (See Dark energy and Cosmic inflation for details.)

ΩΛ (Omega sub lambda)
Instead of the cosmological constant itself, cosmologists often refer to the ratio between the energy density due to the cosmological constant and the critical density of the universe, the tipping point for a sufficient density to stop the universe from expanding forever. This ratio is usually denoted by $ΩΛ$ and is estimated to be $0.689$, according to results published by the Planck Collaboration in 2018.

In a flat universe, $ΩΛ$ is the fraction of the energy of the universe due to the cosmological constant, i.e., what we would intuitively call the fraction of the universe that is made up of dark energy. Note that this value changes over time: The critical density changes with cosmological time but the energy density due to the cosmological constant remains unchanged throughout the history of the universe, because the amount of dark energy increases as the universe grows but the amount of matter does not.

Equation of state
Another ratio that is used by scientists is the equation of state, usually denoted $w$, which is the ratio of pressure that dark energy puts on the universe to the energy per unit volume. This ratio is $w$ = −1 for the cosmological constant used in the Einstein equations; alternative time-varying forms of vacuum energy such as quintessence generally use a different value. The value $w$ = $-1.028$, measured by the Planck Collaboration (2018) is consistent with $-1$, assuming $w$ does not change over cosmic time.

Positive value
Observations announced in 1998 of distance–redshift relation for Type Ia supernovae indicated that the expansion of the universe is accelerating, if one assumes the cosmological principle. When combined with measurements of the cosmic microwave background radiation these implied a value of $Ω_{Λ}$ ≈ 0.7, a result which has been supported and refined by more recent measurements (as well as previous works ). If one assumes the cosmological principle, as in the case for all models that use the Friedmann–Lemaître–Robertson–Walker metric, while there are other possible causes of an accelerating universe, such as quintessence, the cosmological constant is in most respects the simplest solution. Thus, the Lambda-CDM model, the current standard model of cosmology which uses the FLRW metric, includes the cosmological constant, which is measured to be on the order of $m-2$. It may be expressed as $s-2$ (multiplying by $c2$ ≈ $m^{2}⋅s^{−2}$) or as 10−122 ℓ$P$−2 (where ℓ$P$ is the Planck length). The value is based on recent measurements of vacuum energy density, $ρvac$ = $5.96 kg/m3$ ≘ $5.357 J/m3$ = $3.35 GeV/m3$. However, due to the Hubble tension and the CMB dipole, recently it has been proposed that the cosmological principle is no longer true in the late universe and that the FLRW metric breaks down,  so it is possible that observations usually attributed to an accelerating universe are simply a result of the cosmological principle not applying in the late universe.

As was only recently seen, by works of 't Hooft, Susskind and others, a positive cosmological constant has surprising consequences, such as a finite maximum entropy of the observable universe (see Holographic principle).

Quantum field theory
A major outstanding problem is that most quantum field theories predict a huge value for the quantum vacuum. A common assumption is that the quantum vacuum is equivalent to the cosmological constant. Although no theory exists that supports this assumption, arguments can be made in its favor.

Such arguments are usually based on dimensional analysis and effective field theory. If the universe is described by an effective local quantum field theory down to the Planck scale, then we would expect a cosmological constant of the order of $M_{\rm pl}^2$ ($1$  in reduced Planck units). As noted above, the measured cosmological constant is smaller than this by a factor of ~10120. This discrepancy has been called "the worst theoretical prediction in the history of physics".

Some supersymmetric theories require a cosmological constant that is exactly zero, which further complicates things. This is the cosmological constant problem, the worst problem of fine-tuning in physics: there is no known natural way to derive the tiny cosmological constant used in cosmology from particle physics.

No vacuum in the string theory landscape is known to support a metastable, positive cosmological constant, and in 2018 a group of four physicists advanced a controversial conjecture which would imply that no such universe exists.

Anthropic principle
One possible explanation for the small but non-zero value was noted by Steven Weinberg in 1987 following the anthropic principle. Weinberg explains that if the vacuum energy took different values in different domains of the universe, then observers would necessarily measure values similar to that which is observed: the formation of life-supporting structures would be suppressed in domains where the vacuum energy is much larger. Specifically, if the vacuum energy is negative and its absolute value is substantially larger than it appears to be in the observed universe (say, a factor of 10 larger), holding all other variables (e.g. matter density) constant, that would mean that the universe is closed; furthermore, its lifetime would be shorter than the age of our universe, possibly too short for intelligent life to form. On the other hand, a universe with a large positive cosmological constant would expand too fast, preventing galaxy formation. According to Weinberg, domains where the vacuum energy is compatible with life would be comparatively rare. Using this argument, Weinberg predicted that the cosmological constant would have a value of less than a hundred times the currently accepted value. In 1992, Weinberg refined this prediction of the cosmological constant to 5 to 10 times the matter density.

This argument depends on the vacuum energy density being constant throughout spacetime, as would be expected if dark energy were the cosmological constant. There is no evidence that the vacuum energy does vary, but it may be the case if, for example, the vacuum energy is (even in part) the potential of a scalar field such as the residual inflaton (also see Quintessence). Another theoretical approach that deals with the issue is that of multiverse theories, which predict a large number of "parallel" universes with different laws of physics and/or values of fundamental constants. Again, the anthropic principle states that we can only live in one of the universes that is compatible with some form of intelligent life. Critics claim that these theories, when used as an explanation for fine-tuning, commit the inverse gambler's fallacy.

In 1995, Weinberg's argument was refined by Alexander Vilenkin to predict a value for the cosmological constant that was only ten times the matter density, i.e. about three times the current value since determined.

Failure to detect dark energy
An attempt to directly observe and relate quanta or fields like the chameleon particle or the symmetron theory to dark energy, in a laboratory setting, failed to detect a new force. Inferring the presence of dark energy through its interaction with baryons in the cosmic microwave background has also led to a negative result, although the current analyses have been derived only at the linear perturbation regime. It is also possible that the difficulty in detecting dark energy is due to the fact that the cosmological constant describes an existing, known interaction (e.g. electromagnetic field).

title: Cosmological constant