The International Day of Human Space Flight takes place on April 12, 2018 because on the same date in 1961 Yuri Gagarin, a Russian astronaut, was the first human being space flying. The United Nations (UN) chose this date for the International Day of Human Space Flight as a remembrance of this meaningful event. The Soviet Union (Russia), the USA and China are the only nations organizing human space flights.
The International Day of Human Space Flight is considered the start up of the space age and it celebrates the scientific and technical achievement in that industry. It also is reminder of the ambition to use space for only peaceful reasons. Cosmonauts' day also takes place on April the 12th.