December marks the 20th anniversary of one of the most published photographs ever, the 'whole Earth'. Taken on the last mission to the moon, this unique view of the earth was achieveable by the fact that this was the most easterly landing site of any Apollo mission. Previous Apollo astronauts had never seen a complete Earth. The image was taken from about 100,000 kilometres above Earth. the crew, commanded by veteran astronaut Eugene A Cernan, had two Hasselblad cameras which were shared between them. To this day no one knows whether it was Cernan, Ronald E Evans or geologist Harrison H Schmitt who actually pressed the shutter on this image. But 20 years later the 'whole Earth' is still NASA's most requested photograph.