While generally reserved for professional space travelers, the term is sometimes applied to anyone who travels into space, including scientists, politicians, journalists, and tourists.
Until 2003, astronauts were sponsored and trained exclusively by governments, either by the military, or by civilian space agencies. However, with the first sub-orbital flight of the privately-funded SpaceShipOne in 2004, a new category of astronaut was created: the commercial astronaut. With the rise of space tourism, NASA and the Russian Federal Space Agency agreed to use the term "spaceflight participant" to distinguish those space travelers from astronauts on missions coordinated by those two agencies.
The criteria for what constitutes human spaceflight vary. The Fédération Aéronautique Internationale (FAI) Sporting Code for astronautics recognizes only flights that exceed an altitude of . However, in the United States, professional, military, and commercial astronauts who travel above an altitude of are awarded astronaut wings.
As of May 31, 2008, a total of 482 humans from 39 countries have reached 100 km or more in altitude, of which 479 reached Low Earth orbit or beyond. Of these, 24 people have traveled beyond Low Earth orbit, to either lunar or trans-lunar orbit or to the surface of the moon; three of the 24 did so twice (Lovell, Young and Cernan). Under the U. S. definition, 488 people qualify as having reached space. Space travelers have spent over 30,400 person-days (or a cumulative total of over 83 years) in space, including over 100 astronaut-days of spacewalks. As of 2008, the man with the longest time in space is Sergei K. Krikalev, who has spent 803 days, 9 hours and 39 minutes, or 2.2 years, in space. Peggy A. Whitson holds the record for most time in space by a woman, 377 days.
In the United States and many other English-speaking nations, a professional space traveler is called an astronaut. The term derives from the Greek words ástron (άστρον), meaning "star", and nautes (ναύτης), meaning "sailor". The first known use of the term "astronaut" in the modern sense was by Neil R. Jones in his short story The Death's Head Meteor in 1930. The word itself had been known earlier. For example, in Percy Greg's 1880 book Across the Zodiac, "astronaut" referred to a spacecraft. In Les Navigateurs de l'Infini (1925) of J.-H. Rosny aîné, the word astronautique (astronautic) was used. The word may have been inspired by "aeronaut", an older term for an air traveler first applied (in 1784) to balloonists.
NASA applies the term astronaut to any crew member aboard NASA spacecraft bound for Earth orbit or beyond. NASA also uses the term as a title for those selected to join its Astronaut Corps.
By convention, an astronaut employed by the Russian Federal Space Agency (or its Soviet predecessor) is called a cosmonaut in English texts. The word is an anglicisation of the Russian word kosmonavt (космонавт, ), which in turn derives from the Greek words kosmos (κόσμος), meaning "universe", and nautes (ναύτης), meaning "sailor". For the most part, "cosmonaut" and "astronaut" are synonyms in all languages, and the usage of choice is often dictated by political reasons.
On March 14, 1995, Norman Thagard became the first American to ride to space on board a Russian launch vehicle, arguably becoming the first "American cosmonaut" in the process.
See also list of Chinese astronauts
The first human in space was Russian Yuri Gagarin, who was launched into space on April 12, 1961 aboard Vostok 1 and orbited around the Earth. There are allegations that Gagarin ejected from landing module after re-entering the atmosphere and parachuted back, due to safety concerns about the craft's landing systems. The first woman in space was Russian Valentina Tereshkova, launched in June 1963 aboard Vostok 6.
Alan Shepard became the first American and second person in space on May 5, 1961, while the first American woman in space was Sally Ride, during Space Shuttle Challenger's mission STS-7, on June 18, 1983.
The first mission to orbit the moon was Apollo 8, which included William Anders who was born in Hong Kong, making him the first Asian-born astronaut in 1968. In April 1985, Taylor Wang became the first ethnic Chinese person in space. On 15 October 2003, Yang Liwei became China's first astronaut on the Shenzhou 5 spacecraft.
The Soviet Union, through its Intercosmos program, allowed people from other socialist countries to fly on its missions. An example is Vladimír Remek, a Czechoslovak, who became the first non-Soviet European in space in 1978 on a Russian Soyuz rocket. On July 23, 1980, Pham Tuan of Vietnam became the first Asian in space when he flew aboard Soyuz 37. Also in 1980, Cuban Arnaldo Tamayo Méndez became the first person of African descent to fly in space (the first person born in Africa to fly in space was Patrick Baudry, in 1985). In 1988, Abdul Ahad Mohmand became the first Afghan to reach space, spending nine days aboard the Mir space station.
With the larger number of seats available on the Space Shuttle, the U.S. began taking international astronauts. In 1985, Rodolfo Neri Vela became the first Mexican-born person in space. In 1991, Helen Sharman became the first Briton to fly in space. In 2002, Mark Shuttleworth became the first citizen of an African country to fly in space, as a paying spaceflight participant. In 2003, Ilan Ramon became the first Israeli to fly in space.
The youngest person to fly in space is Gherman Titov, who was 25 years old when he flew Vostok 2. (Titov was also the first person to suffer space sickness). The oldest person who has flown in space is John Glenn, who was 77 when he flew on STS-95. The longest stay in space was 438 days, by Russian Valeri Polyakov. As of 2006, the most spaceflights by an individual astronaut is seven, a record held by both Jerry L. Ross and Franklin Chang-Diaz. The furthest distance from Earth an astronaut has traveled was 401,056 km, during the Apollo 13 emergency.
Once selected, NASA astronauts go through 20 months of training in a variety of areas, including training for extra-vehicular activity in a facility such as NASA's Neutral Buoyancy Laboratory. Astronauts-in-training may also experience short periods of weightlessness in aircraft called the "vomit comet", the nickname given to a pair of modified KC-135s (retired in 2000 and 2004 respectively, and replaced in 2005 with a C-9) which perform parabolic flights. Astronauts are also required to accumulate a number of flight hours in high-performance jet aircraft. This is mostly done in T-38 jet aircraft out of Ellington Field, due to its proximity to the Johnson Space Center. Ellington Field is also where the Shuttle Training Aircraft is maintained and developed, although most flights of the aircraft are done out of Edwards Air Force Base.
Mission Specialist Educators, or "Educator Astronauts", were first selected in 2004, and as of 2007, there are three NASA Educator astronauts: Joseph M. Acaba, Richard R. Arnold, and Dorothy Metcalf-Lindenburger. Barbara Morgan, selected as back-up teacher to Christa McAuliffe in 1985, is considered to be the first Educator astronaut by the media, but she trained as a mission specialist. The Educator Astronaut program is a successor to the Teacher in Space program from the 1980s.
A memorial at the Kennedy Space Center, Florida, USA, commemorates "24 U.S. astronauts who gave their lives for space exploration.