TLDR: Astronauts are people who go to space. They are trained and equipped to travel on spacecraft and can be commanders or crew members. The term "astronaut" is used for space travelers from any country, while "cosmonaut" is used specifically for Russian or Soviet space travelers. China has its own term, "taikonaut." There have been over 600 astronauts who have flown in space since 1961.

Astronauts are people who have been trained to go to space. The word "astronaut" comes from the Greek words for "star" and "sailor." It is used to describe anyone who travels into space, whether they are scientists, politicians, journalists, or tourists. The term technically applies to all human space travelers, regardless of nationality. However, Russian and Soviet space travelers are usually called "cosmonauts," and Chinese space travelers are called "taikonauts."

Since 1961, over 600 astronauts have flown in space. In the past, astronauts were sponsored and trained exclusively by governments. But in 2004, a new category of astronaut was created: the commercial astronaut. These are people who are privately funded and trained to go to space.

To be considered an astronaut, you have to meet certain criteria. The exact criteria vary, but generally, it involves traveling above a certain altitude, such as 100 kilometers (62 miles). In the United States, astronauts who travel above 80 kilometers (50 miles) are awarded astronaut wings. As of 2016, over 550 people from 36 countries have reached this altitude or higher.

There have been many milestones in space travel. The first human in space was Yuri Gagarin, a Soviet cosmonaut, who orbited the Earth for 108 minutes in 1961. The first woman in space was Valentina Tereshkova, also a Soviet cosmonaut, who orbited the Earth for almost three days in 1963. The first American in space was Alan Shepard, who made a sub-orbital flight in 1961. The first American to orbit the Earth was John Glenn in 1962.

There have also been civilian and non-governmental milestones in space travel. The first civilian in space was Valentina Tereshkova, and the first non-governmental space traveler was Mike Melvill, who piloted SpaceShipOne on a suborbital journey. There have also been self-funded space travelers, such as Dennis Tito, who paid to fly to the International Space Station in 2001.

Astronauts go through extensive training before they can go to space. This includes training for extravehicular activities (spacewalks) and experiencing weightlessness in an aircraft called the "Vomit Comet." They also accumulate flight hours in high-performance jet aircraft.

In summary, astronauts are people who are trained and equipped to go to space. The term "astronaut" is used for space travelers from any country, while "cosmonaut" is used specifically for Russian or Soviet space travelers. There have been over 600 astronauts who have flown in space since 1961. They go through extensive training before they can go to space.