Carl Sagan: You Are Here (Pale Blue Dot)

Carl Sagan on the opening image, taken by NASA using the Voyager probe at his request:  

The spacecraft was a long way from home. I thought it might be a good idea just after Saturn to have them take one last glance homeward. 

From Saturn, the Earth would appear too small for Voyager to make out any detail. Our planet would just be a point of light, a lonely pixel, hardly distinguishable from the many other points of light Voyager would see – nearby planets, far-off suns. 

But precisely because of the obscurity of our world, thus revealed, such a picture might be worth having. It had been well-understood by the scientists and philosophers of classical antiquity that the Earth was a mere point in a vast encompassing cosmos. But no one had ever seen it as such. Here was our first chance, and perhaps also our last for decades to come.