Apollo 8: Earthrise
It was December of 1968 that Apollo 8 orbited the moon. For the first time, the people of earth witnessed Earthrise over the lunar surface. The image would have a profound impact on humanity. The image is still used as a popular background on new or refurbished computers everywhere.
An excellent book on this subject, Genesis : The Story of Apollo 8 : The First Manned Flight to Another World talks about this profound impact from the context of the Cold War Era.