darker than a moonless night on Earth).

When the first astronauts travelled out to the Moon during the Apollo 8 mission and flew into the shadow behind it on 24 December 1968, the darkness of the unlit side was so profound that the Moon was invisible to the crew, in orbit around it, who could only detect a black circular silhouette surrounded by millions of stars not normally visible on Earth. Bill Anders later described how he only became aware of the Moon when he