The limits of the possible can only be defined by going beyond them into the impossible.

When the Sun shrinks to a dull red dwarf, it will not be dying. It will just be starting to live and everything that has gone before will merely be a prelude to its real history.

I'm sure we would not have had men on the Moon if it had not been for Wells and Verne and the people who write about this and made people think about it. I'm rather proud of the fact that I know several astronauts who became astronauts through reading my books.

It was the mark of a barbarian to destroy something one could not understand.

The best measure of a man's honesty isn't his income tax return. It's the zero adjust on his bathroom scale.

Trying to predict the future is a discouraging and hazardous occupation. If by some miracle a prophet could describe the future exactly as it was going to take place, his predictions would sound so absurd that people everyone would laugh him to scorn. The only thing we can be sure of about the future is that it will be absolutely fantastic. So, if what I say now seems to you to be very reasonable, then I will have failed completely. Only if what I tell you appears absolutely unbelievable have we any chance of visualizing the future as it really will happen.

There is hopeful symbolism in the fact that flags do not wave in a vacuum.