Explanation

 on July 20, 1969 at 20:17 UTC. That day the first human beings landed on the moon

Neil Armstrong and Edwin "Buzz" Aldrin were the first of 12 human beings to walk on the Moon

Armstrong became the first person to step onto the lunar surface six hours and 39 minutes later on July 21 at 02:56 UTC;

Aldrin joined him 19 minutes later.