Of the multitude of stunning images from space, one of the most memorable is a photo - taken in 1968 by astronaut William Anders - of a radiant blue-and-white sphere slowly appearing above the horizon of the Moon.
This image of Earth's rise inspired the creation of Earth Day, which - 50 years on - is being celebrated by NASA.
Corin Dann spoke earlier to NASA scientist Dr Annmarie Eldering and asked if we'd successfully done anything to protect our fragile planet.
