... chemistry is a trade for people without enough imagination to be physicists.

It was one thing to have guessed it, another to have had that guess confirmed beyond possibility of refutation.

Behind every man now alive stand thirty ghosts, for that is the ratio by which the dead outnumber the living.

The exploration of the planets is now closer to us in time than the exploration of Africa by Stanley and Livingstone.

Before the current decade ends, fee-paying passengers will be experiencing suborbital flights aboard privately funded vehicles. . . . It won't be too long before bright young men and women set their eyes on careers in Earth orbit and say: "I want to work 200 kilometers from home-straight up!"

In my life I have found two things of priceless worth - learning and loving. Nothing else - not fame, not power, not achievement for its own sake - can possible have the same lasting value. For when your life is over, if you can say 'I have learned' and 'I have loved,' you will also be able to say 'I have been happy.

When beauty is universal, it loses its power to move the heart, and only its absence can produce any emotional effect.