On Christmas Eve in 1968, Apollo 8 astronaut William Anders took a photo that changed humanity's perception of the world.The image known as "Earthrise" showed our home planet as a half-illuminated sphere, slowly lifting itself above the Moon's cold horizon.As Anders scrambled for a colour film roll on the far side of the Moon, the planet he was photographing was in geopolitical turmoil.The United States was mired in an increasingly unpopular war in Vietnam; Martin Luther King Jr and Robert F Kennedy had been assassinated; there was conflict and unrest in the Eastern Bloc, South Africa, Northern Ireland, India and…