An astronaut is a person trained for space travel. They can be specialists for commanding or piloting, crew members or perform other activities in space.
In 1957 the dog Laika became the first living being in space, travelling on board of the satellite Sputnik 2.
Scientists intended to asses the survival conditions of a living being in space. Unfortunately, after one week on board of Sputnik 2, the oxygen became insufficient causing Laika’s death.
Nevertheless, this fact did not discouraged astronauts from traveling into the space later on, enabling to improve the spaceship performance.
The first astronaut in space: Yuri Gargarin
The USA didn´t want to stay behind the ex-Soviet Union and this had an effect on their program to overcome their rivals.
Then the Apollo missions began where the USA intended to send the first human to the Moon. In 1969, people all around the world watched live on TV Neil Armstrong and Edwin Aldin performing this historical achievement.
Before astronauts are ready to travel into space they need to attend at training, during which they study several things such as physics, mathematics, meteorology, astronomy, electronics, aeronautics and informatics.
The absence of gravity causes bone decalcification and muscle mass loss, as the bones don´t have to support the body weight. For this reason the activity of the cells responsible for the bone formation diminishes, increasing the likelihood of these to break when the astronauts return to Earth.
I order to simulate space conditions astronauts train in water tanks, where they learn to float and carry out their tasks without the gravity effect.