As Neil Armstrong became the first man to walk on the moon, a global audience of 500 million people were watching and listening. "That's one small step for man, one giant leap for mankind," they heard him say as he dropped from the ladder of his spacecraft to make the first human footprint on the lunar surface. It was the perfect quote for such a momentous occasion. But from the moment he said it, people have argued about whether the NASA astronaut got his lines wrong. In the tense six hours and forty minutes between landing on the moon and stepping out of the capsule, Armstrong wrote what he knew would become some of the most memorable words in history. He has always insisted that he wrote "one small step for a man, one giant leap for mankind," which would have been a more meaningful and grammatically correct sentence. Without the missing "a," the intended meaning of the sentence is lost. In effect, the line means, "That is one small step for mankind (i.e., humanity), one giant leap for mankind." But did he really say the sentence incorrectly? Until now Armstrong himself had never been sure if he actually said what he wrote. In his biography First Man he told the author James Hansen, "I must admit that it doesn't sound like the word 'a' is there. On the other hand, certainly the 'a' was intended, because that's the only way it makes sense." But now, after almost four decades, the space explorer has been 39 .