By exploring other worlds we safeguard this one. By itself, I think this fact more than justifies the money our species has spent in sending ships to other worlds. It is our fate to live during one of the most perilous and, at the same time, one of the most hopeful chapters in human history.

So those who wished for some central cosmic purpose for us, or at least our world, or at least our solar system, or at least our galaxy, have been disappointed, progressively disappointed. The universe is not responsive to our ambitious expectations.

The Earth is a place. It is by no means the only place. It is not even a typical place.

I think if we ever reach the point where we think we thoroughly understand who we are and where we came from, we will have failed.

Exploration is in our nature. We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars.

If the greenhouse effect is a blanket in which we wrap ourselves to keep warm, nuclear winter kicks the blanket off.

In the middle 1970s an astronomer I admire put together a modest manifesto called "Objections to Astrology" and asked me to endorse it. I struggled with his wording, and in the end found myself unable to sign, not because I thought astrology has any validity whatever, but because I felt (and still feel) that the tone of the statement was authoritarian.