People have dreamt of travelling in space for thousands of years, but it didn't become a reality until about 40 years ago.
On 12 April, 1961, the Russian cosmonaut Yuri Gagarin blasted off into orbit in his Vostok 1 spacecraft.
He circled the Earth once at an altitude of 320 km (200 miles).
"The Earth is blue," he said in awe.