A cosmonaut is a person who is trained to operate spacecraft and conduct experiments in outer space. The term cosmonaut is used to refer to a Russian ASTRONAUT, while the term ASTRONAUT is used to refer to an American ASTRONAUT. Cosmonauts are also known as spacemen or astronauts, depending on their nationality. Cosmonauts have been involved in many space exploration missions, including the first human spaceflight in 1961. They have also conducted research in fields such as astronomy, physics, and biology.